Electronics Manufacturing Technical Articles

An Innovative Reliability Solution to Interconnect of Flexible/Rigid Substrates

Jan 12, 2016 | Dr. Mary Liu and Dr. Wusheng Yin

With the pitch size of interconnect getting finer and finer, the bonding strength between flexible and rigid (e.g. PCB, ceramic) substrates becomes a serious issue because it is not strong enough to meet the customer’s requirement. Capillary underfill has been used to enhance the bonding strength between flexible and rigid substrates, but the enhancement is very limited, particularly for high temperature application. The bonding strength of underfilled flexible/rigid interconnect is dramatically decreased after being used at 180◦C, and the interconnects are weakened by the internal stress caused by the expansion of underfill at high temperatures. In order to resolve reliability issues of the interconnect between flexible/rigid substrates, solder joint encapsulant was implemented into the thermal compression bonding process, which was used to manufacture the interconnect between flexible/rigid substrates. Compared to the traditional process, the strength of the interconnect was doubled and the reliability was significantly improved in high temperature application....

Publisher: YINCAE Advanced Materials, LLC.

Solder Joint Encapsulant Adhesive - LGA High Reliability And Low Cost Assembly Solution

Jan 12, 2016 | Dr. Mary Liu and Dr. Wusheng Yin

More and more Land Grid Array (LGA) components are being used in electronic devices such as smartphones, tablets and computers. In order to enhance LGA mechanical strength and reliability, capillary flow underfill is used to improve reliability. However, due to the small gap, it is difficult for capillary underfill to flow into the LGA at SMT level. Due to cost considerations, there are usually no pre-heating underfill or cleaning flux residue processes at the SMT assembly line. YINCAE solder joint encapsulant SMT256 has been successfully used with solder paste for LGA assembly. Solder joint encapsulant is used in in-line LGA soldering process with enhanced reliability. It eliminates the underfilling process and provides excellent reworkability. The shear st rength of solder joint is stronger than that of underfilled components. The thermal cycling performance using solder joint encapsulant is much better than that using underfill. Bottom IC of POP has been studied for further understanding of LGA assembly process parameters. All details such as assembly process, drop test and thermal cycling test will be discussed in this paper....

Publisher: YINCAE Advanced Materials, LLC.

The Future of Solder Joint Encapsulant

Jan 08, 2016 | Dr. Mary Liu and Dr. Wusheng Yin

Solder joint encapsulant adhesives have been successfully used to enhance the strength of solder joints and improve thermal cycling as well as drop performance in finished products. The use of solder joint encapsulant adhesives can eliminate the need for underfill materials and the underfill process altogether, thus simplifying rework, which results in a lower cost of ownership.

Solder joint encapsulant adhesives include: low temperature and high temperature solder joint encapsulant adhesives, and their derivatives. Each solder joint encapsulant adhesive has: unfilled and filled solder joint encapsulant adhesives, and solder joint encapsulant paste. Each solder joint encapsulant product has been designed for different applications. In this paper, we are going to discuss the details and future of solder joint encapsulant adhesives. ...

Publisher: YINCAE Advanced Materials, LLC.

Effect on Microwave Plasma Surface Treatment for Improved Adhesion Strenght of Direct Copper Plating on Polytetrafluoroethylene (PTFE)

Jan 07, 2016 | Akira Takeuchi, Takahiro Kurahashi, Kyosuke Takeda

The purpose of this study is to investigate the effect of plasma surface modification to improve adhesion strength between polytetrafluoroethylene (PTFE) and electroless copper plating. PTFE is widely used in many industries because of its unique electrical, thermal, and mechanical characteristics. However, because of its low surface energy, it is difficult to acquire enough adhesion strength between PTFE and other substances without surface modification. Plasma is well known as one of the surface modification techniques that improve adhesion strength....

Publisher: Nissin Corporation

Study on Solder Joint Reliability of Fine Pitch CSP

Dec 31, 2015 | Yong Hill Liang, Hank Mao, YongGang Yan, Jindong (King) Lee; AEG, Flextronics International.

Today's consumer electronic product are characterized by miniatuization, portability and light weight with high performance, especially for 3G mobile products. In the future more fine pitch CSPs (0.4mm) component will be required. However, the product reliability has been a big challenge with the fine pitch CSP. Firstly, the fine pitch CSPs are with smaller solder balls of 0.25mm diameter or even smaller. The small solder ball and pad size do weaken the solder connection and the adhesion of the pad and substrate, thus the pad will peel off easily from the PCB substrate. In addition, miniature solder joint reduce the strength during mechanical vibration, thermal shock, fatigue failure, etc. Secondly, applying sufficient solder paste evenly on the small pad of the CSP is difficult because stencil opening is only 0.25mm or less. This issue can be solved using the high end type of stencil such as Electroforming which will increase the cost....

Publisher: Flex (Flextronics International)

PCB Fabrication Processes and Their Effects on Fine Copper Barrel Cracks

Dec 23, 2015 | Edward Arthur, Charles Busa, Melissa Durfee, Chad Gibson, Wade Goldman P.E.; Raytheon Company, Space and Airborne Systems, The Charles Stark Draper Laboratory, Inc., Raytheon Company, Integrated Defense Systems.

The onset of copper barrel cracks is typically induced by the presence of manufacturing defects. In the absence of discernible manufacturing defects, the causes of copper barrel cracks in printed circuit board (PCB) plated through holes is not well understood. Accordingly, there is a need to determine what affects the onset of barrel cracks and then control those causes to mitigate their initiation.

The objective of this research is to conduct a design of experiment (DOE) to determine if there is a relationship between PCB fabrication processes and the prevalence of fine barrel cracks. The test vehicle used will be a 16-layer epoxy-based PCB that has two different sized plated through holes as well as buried vias....

Publisher: Raytheon

Good Product Quality Comes From Good Design for Test Strategies

Dec 17, 2015 | Adrian Cheong

Product quality can be improved through proper application of design for test (DFT) strategies. With today's shrinking product sizes and increasing functionality, it is difficult to get good test coverage of loaded printed circuit boards due to the loss of test access. Advances in test techniques, such as boundary scan, help to recover this loss of test coverage. However, many of these test techniques need to be designed into the product to be effective.

This paper will discuss how to maximize the benefits of boundary scan test, including specific examples of how designers should select the right component, connect multiple boundary scan components in chains, add test access to the boundary scan TAP ports, etc. A discussion of DFT guidelines for PCB layout designers is also included. Finally, this paper will include a description of some advanced test methods used in in-circuit tests, such as vectorless test and special probing methods, which are implemented to improve test coverage on printed circuit boards with limited test access....

Publisher: Agilent Technologies, Inc.

Looking Forward - Manufacturing Execution Systems for SME’s

Dec 14, 2015 | Pete Doyon, VP Product Management, Schleuniger, Inc.

A Manufacturing Execution System (MES) is a software program that manages and monitors production work in a factory. The MES controls and monitors all manufacturing data in real time, so there is no guesswork as to the status of any given job, machine, operator, etc. The focus is on short-interval scheduling (shift or day) with an emphasis on optimizing the distribution of work orders. Larger manufacturers have employed MES’s for years but many small to medium sized enterprises (SME’s) have yet to adopt such systems. The benefits of using an MES are many. Looking forward, I predict that even the smallest manufacturing companies will employ MES systems in the future....

Publisher: Schleuniger, Inc.

Packaging Technology and Design Challenge for Fine Pitch Micro-Bump Cu-Pillar and BOT (Direct Bond on Substrate-Trace) Using TCNCP

Dec 02, 2015 | Myung-June Lee -Altera Corporation, SungSoon Park, DongSu Ryu, MinJae Lee - Amkor Technology, Hank Saiki, Seiji Mori, Makoto Nagai - NTK Technologies.

(Thermal Compression with Non-Conductive Paste Underfill) Method.

The companies writing this paper have jointly developed Copper (Cu) Pillar micro-bump and TCNCP(Thermal Compression with Non-Conductive Paste) technology over the last two+ years. The Cu Pillar micro-bump and TCNCP is one of the platform technologies, which is essentially required for 2.5D/3D chip stacking as well as cost effective SFF (small form factor) package enablement.

Although the baseline packaging process methodology for a normal pad pitch (i.e. inline 50μm) within smaller chip size (i.e. 100 mm2) has been established and are in use for HVM production, there are several challenges to be addressed for further development for commercialization of finer bump pitch with larger die (i.e. ≤50μm tri-tier bond pad with the die larger than 400mm2).

This paper will address the key challenges of each field, such as the Cu trace design on a substrate for robust micro-joint reliability, TCNCP technology, and substrate technology (i.e. structure, surface finish). Technical recommendations based on the lessons learned from a series of process experimentation will be provided, as well. Finally, this technology has been used for the successful launching of the company FPGA products with SFF packaging technology....

Publisher: Altera Corporation

HCFC-225 Phaseout - What Now?

Dec 01, 2015 | Ed Kanegsberg

On January 1, 2015, nine months from APEX 2014, the production and use restrictions on HCFC-225 will be in effect throughout the United States. This phase out is encompassing in scope. This phase out will have significant technical, performance, and economic implications for the electronics industry. The regulatory situation remains fluid. A number of alternative solvents have been or are in the process of being developed. We discuss the options for assemblers and component manufacturers....

Publisher: BFK Solutions LLC

Study of Various PCBA Surface Finishes

Nov 25, 2015 | Georgie Thein, David Geiger, and Murad Kurwa.

In this study various printed circuit board surface finishes were evaluated, including: organic solderability preservative (OSP), plasma finish (PF), immersion silver (IAg), electroless nickel / immersion silver (ENIS), electroless nickel / immersion gold hi-phosphorus (ENIG Hi-P), and electroless nickel / electroless palladium / immersion gold (ENEPIG). To verify the performance of PF as a post-treatment option, it was added to IAg, ENIG Hi-P, and ENEPIG to compare with non-treated. A total of nine groups of PCB were evaluated. Each group contains 30 boards, with the exception on ENIS where only 8 boards were available....

Publisher: Flex (Flextronics International)

HALT Testing of Backward Soldered BGAs on a Military Product

Nov 19, 2015 | B. Gumpert, B. Fox, L. Woody

The move to lead free (Pb-free) electronics by the commercial industry has resulted in an increasing number of ball grid array components (BGAs) which are only available with Pb-free solder balls. The reliability of these devices is not well established when assembled using a standard tin-lead (SnPb) solder paste and reflow profile, known as a backward compatible process. Previous studies in processing mixed alloy solder joints have demonstrated the importance of using a reflow temperature high enough to achieve complete mixing of the SnPb solder paste with the Pb-free solder ball. Research has indicated that complete mixing can occur below the melting point of the Pb-free alloy and is dependent on a number of factors including solder ball composition, solder ball to solder paste ratio, and peak reflow times and temperatures. Increasing the lead content in the system enables full mixing of the solder joint with a reduced peak reflow temperature, however, previous research is conflicting regarding the effect that lead percentage has on solder joint reliability in this mixed alloy solder joint....

Publisher: Lockheed Martin Corporation

The Perfect Copper Surface

Nov 12, 2015 | Eric Stafstrom; Technic Inc, Garo Chehirian; Tech-Etch.

In order to provide the functionality in today’s electronics, printed circuit boards are approaching the complexity of semiconductors. For flexible circuits with 1 mil lines and spaces, this means no nodules, no pits, and excellent ductility with thinner deposits. One of the areas that has to change to get to this plateau of technology is acid copper plating. Acid copper systems have changed in minor increments since their introduction decades ago. However, the basic cell design using soluble anodes in slabs or baskets has for the most part remained the same. Soluble, phosphorized, copper anodes introduce particulate and limits the ability to control plating distribution....

Publisher: Technic Inc.

Print Performance Studies Comparing Electroform and Laser-Cut Stencils

Nov 05, 2015 | Rachel Miller Short, William E. Coleman Ph.D.; Photo Stencil | Joseph Perault; Parmi.

There has been recent activity and interest in Laser-Cut Electroform blank foils as an alternative to normal Electroform stencils. The present study will investigate and compare the print performance in terms of % paste transfer as well the dispersion in paste transfer volume for a variety of Electroform and Laser-Cut stencils with and without post processing treatments. Side wall quality will also be investigated in detail. A Jabil solder paste qualification test board will be used as the PCB test vehicle....

Publisher: Photo Stencil LLC

Novel Approaches for Minimizing Pad Cratering

Oct 29, 2015 | Chen Xu, Yunhu Lin; Alcatel-Lucent, Yuan Zeng, Pericles A. Kondos; Unovis-Solutions.

With the electronic industry moving towards lead-free assembly, traditional SnPb-compatible laminates need to be replaced with lead-free compatible laminates that can withstand the higher reflow temperature required by lead-free solders. Lead-free compatible laminates with improved heat resistance have been developed to meet this challenge but they are typically more brittle than SnPb laminates causing some to be more susceptible to pad cratering. In this paper, two novel approaches for minimizing pad cratering will be discussed. Preliminary results which validate the two approaches will also be presented....

Publisher: Alcatel-Lucent

Tin Whisker Risk Management by Conformal Coating

Oct 22, 2015 | Linda Woody, William Fox; Lockheed Martin Missiles and Fire Control

The objective of this study is to evaluate conformal coatings for mitigation of tin whisker growth. The conformal coatings chosen for the experiment are acrylic, polyurethane and parylene. Also included in this paper are tin whisker inspection results of tin-plated braiding and wire that was exposed to an environment of 50°C with 50% relative humidity for over five years....

Publisher: Lockheed Martin Corporation

Optimizing the Insulated Metal Substrate Application with Proper Material Selection and Circuit Fabrication

Oct 15, 2015 | Dave Sommervold, Chris Parker, Steve Taylor, Garry Wexler

The ever expanding growth in the use of insulated metal substrates (IMS) in power electronics requires a focus on material and mechanical configuration for each application. By optimizing the material makeup and printed board format, performance and reliability expectations can be further achieved. The thermal performance and electrical isolation needs are driven by the power requirements, but considerations of temperature range, mechanical durability and format, along with the physical package surrounding the substrate must also be managed. With a variety of material configurations and circuit format capabilities, the choices become a balancing of options to maximize performance and minimizing cost through Design For Manufacturability (DFM) in the circuit board fabrication. These challenges present the IMS printed board fabricator with material selections and fabrication processes unlike those for other printed board or ceramic applications....

Publisher: The Bergquist Company

Preparing for Increased Electrostatic Discharge Device Sensitivity

Oct 08, 2015 | Julian A. Montoya, Intel Corporation Hillsboro, Oregon

With the push for ever improving performance on semiconductor component I/O interfaces, semiconductor components are being driven into a realm which makes them more sensitive to electrostatic discharge, potentially increasing in sensitivity by 50% every 3-5 years. Today, the majority of modern day semiconductor components are being designed to meet 250Volts of charge device model sensitivity, and that could decrease to 125Volts in the next 3-5 years, and could again decrease to 50Volts-70Volts in the following 3-5 years. The entire electronics industry must prepare for this challenge....

Publisher: Intel Corporation

Printing of Solder Paste - A Quality Assurance Methodology

Oct 01, 2015 | Lars Bruno and Tord Johnson Ericsson AB and MTEK Consulting AB

Solder paste printing is known to be one of the most difficult processes to quality assure in electronic manufacturing. The challenge increases as the technology development moves toward a mix between large modules and small chip components on large and densely populated printed circuit boards. Having a process for quality assurance of the solder paste print is fast becoming a necessity.

This article describes a method to ensure quality secured data from both solder paste printers and inspection machines in electronic assembly manufacturing. This information should be used as feedback in order to improve the solder paste printing process....

Publisher: Ericsson AB

Gold Stud Bump Flip Chip Bonding on Molded Interconnect Devices

Sep 23, 2015 | Dick Pang, Weifeng Liu, Anwar Mohammed, Elissa Mckay, Teresita Villavert and Murad Kurwa

A molded interconnect device (MID) is an injection molded thermoplastic substrate which incorporates a conductive circuit pattern and integrates both mechanical and electrical functions. (...) Flip chip bonding of bare die on MID can be employed to fully utilize MID’s advantage in device miniaturization. Compared to the traditional soldering process, thermo-compression bonding with gold stud bumps provides a clear advantage in its fine pitch capability. However, challenges also exist. Few studies have been made on thermocompression bonding on MID substrate, accordingly little information is available on process optimization, material compatibility and bonding reliability. Unlike solder reflow, there is no solder involved and no “self-alignment,” therefore the thermo-compression bonding process is significantly more dependent on the capability of the machine for chip assembly alignment....

Publisher: Flex (Flextronics International)

Method for the Manufacture of an Aluminum Substrate PCB and its Advantages

Sep 17, 2015 | Joseph Fjelstad

RoHS legislated restrictions on the materials used in electronics manufacture have imparted significant challenges on the electronics industry since their introduction in 2006. The greatest impacts have been felt by the mandated elimination of lead from electronic solder followed by the demand for the elimination of haloids from flame retardants used in traditional PCB laminates. In the years which have followed the electronics industry has been beset with a host of new challenges in its effort to comply. Failure mechanisms, both new and old, have surfaced which demand solution and the industry suppliers and manufacturing technologists have worked diligently to remedy those vexing faults through the development of a wide range of new materials and equipment for both board manufacture and assembly, along with modifications to the processes used in the manufacture and assembly of printed circuit boards....

Publisher: Verdant Electronics

New High-Performance Organophosphorus Flame Retardant

Sep 10, 2015 | Kimberly M. White, Ph.D., Daniel De Schryver, Ph.D., and Randy Chaya

A new non-halogen flame retardant has been developed and is useful for a variety of high performance applications. This non-reactive phosphorus-based material satisfies fire safety needs for a broad range of resins including epoxy, polyolefin, and polyamide. The combination of excellent flame retardant efficiency, high thermal stability and exceptional electrical properties is unique to this organophosphorus flame retardant and makes it a breakthrough technology for high speed, high frequency use in fast growing wireless and wired infrastructures. Resin performance data, including formulations with synergists, are presented in this paper....

Publisher: Albemarle Corporation

Embedded Fibers Enhance Nano-Scale Interconnections

Sep 03, 2015 | V. Desmaris, S. Shafiee, A. Saleem, A. Johansson and P. Marcoux

While the density of chip-to-chip and chip-to-package component interconnections increases and their size decreases the ease of manufacture and the interconnection reliability are being reduced. This paper will introduce the use of embedded fibers in the interconnections as a means of addressing these issues....

Publisher: Smoltek AB

Adhesive Backed Plastic Stencils vs Mini Metal Stencils

Aug 27, 2015 | Bob Wettermann, MIT

Ever since there has been a widespread usage of surface mount parts, the trend of continued shrinkage of devices with ever finer pitches has continued to challenge PCB assemblers for the rework of same. Todays' pitches are commonly 0.5 to 0.4mm with packages of tiny outline sizes, 5 -10mm square, making the rework of such devices a challenge. In addition to the handling and inspection challenges comes the board density. Spacing to neighboring components continues to be compressed so the rework techniques should not damage neighboring components....

Publisher: BEST Inc.

Challenges for Step Stencils with Design Guidelines for Solder Paste Printing

Aug 25, 2015 | Carmina Läntzsch, Georg Kleemann

The stencil printing process is one of the most critical processes in the electronic production. Due to the requirement: "faster and smaller" it is necessary to place components with different paste volume close together without regard to solder paste printing. In our days it is no longer possible to control the solder paste volume only by adjustment of the aperture dimensions. The requirements of solder paste volumes for specific components are realized by different thicknesses of metal sheets in one stencil with so called step stencils. The step-down stencil is required when it is desirable to print fine-pitch devices using a thinner stencil foil, but print other devices using a thicker stencil foil.

The paper presents the innovative technology of step-up and step-down stencils in a laser cutting and laser welding process. The step-up/step-down stencil is a special development for the adjustment of solder paste quantity, fulfilling the needs of placement and soldering. This includes the laser cutting and laser welding process as well as the resulting stencil characteristics and the potential of the printing process....

Publisher: LaserJob

SELECT CONFORMAL COAT FORMULATION FOR PCB ENVIRONMENT

Aug 20, 2015 | Wes Noble

Temperature and Humidity on Selective Conformal Coating It is well known that selective conformal coating on printed circuit board (PCB) assemblies provides unparallel protection for PCB’s. Nevertheless, concentrated conditions of humidity, water, and high temperatures can have negative effects on the conformal coating itself causing it to fail and become inapt for its intended purpose. Taking this into consideration, it is prudent to choose the right type of conformal coating that best suits the application and environmental conditions under which an assembly is likely to undergo in use. The proper conformal coating will significantly reduce the likelihood of failure/rejection, saving both valuable time and money for any manufacturing process....

Publisher: ETS - Energy Technology Systems, Inc.

Implementing Robust Bead Probe Test Processes into Standard Pb-Free Assembly

Aug 20, 2015 | John McMahon P.Eng, Tom Blaszczyk, Peter Barber

Increasing system integration and component densities continue to significantly reduce the opportunity to access nets using standard test points. Over time the size of test points has been drastically reduced (as small as 0.5 mm in diameter) but current product design parameters have created space and access limitations that remove even the option for these test points. Many high speed signal lines have now been restricted to inner layers only. Where surface traces are still available for access, bead probe technology is an option that reduces test point space requirements as well as their effects on high speed nets and distributes mechanical loading away from BGA footprints enabling test access and reducing the risk of mechanical defects associated with the concentration of ICT spring forces under BGA devices.

Building on Celestica's previous work characterizing contact resistance associated with Pr-free compatible surface finishes and process chemistry; this paper will describe experimentation to define a robust process window for the implementation of bead probe and similar bump technology that is compatible with standard Pb-free assembly processes. Test Vehicle assembly process, test methods and "Design of Experiments" will be described. Bead Probe formation and deformation under use will also be presented along with selected results....

Publisher: Celestica Corporation

NON-CONTACT FLUID DISPENSING WITH PS-8200 JETTING VALVE

Aug 18, 2015 | Brian Stumm

Jetting Valve Technology Superior to Needle Dispensing Compared to traditional needle dispensing technology, jetting valve technology is the most effective method for quick and accurate fluid dispensing. Injection technology has many advantages, it provides a combination of high-speed, high quality and low cost production for fluid dispensing processes. Instead of putting focus on getting the application done, jet dispense technology focuses on performance, providing applications like underfill, potting and encapsulation with more precision than ever before. Improved Fluid Dispensing Speed and Accuracy Non-contact jetting valves offer a significant advantage over traditional needle dispense valves. Jetting Valve Dispenser precision reaches to 200µm with dot diameter or line width as small as 250µm and volumetric dispensing down to .0036µl. Minimum space between lines is 180µm and maximum fluid dispense speed is 200 dots/second. The following video illustrates quick, accurate fluid dispensing for an LED packaging application....

Publisher: ETS - Energy Technology Systems, Inc.

CONFORMAL COATING FOR WATER RESISTANT CIRCUIT ASSEMBLIES

Aug 18, 2015 | Brian Stumm

Why Selectively Conformal Coat the Electronic Assembly? Printed circuit boards (PCBs) are employed in a variety of products and devices, and this means that it might be necessary for your PCBs to be moisture resistant. It is important to choose the right type of conformal coating so you need not worry about the durability of your product. Fortunately, there are several options available that can help, and you can even use selective conformal coating robots to provide proper application of the coating....

Publisher: ETS - Energy Technology Systems, Inc.

ULTRAVIOLET (UV) CURING TECHNOLOGY

Aug 18, 2015 | Wes Noble

What is UV Curing? “Ultraviolet (UV) light is an electromagnetic radiation with a wavelength from 400 nm to 100 nm, shorter than that of visible light but longer than X-rays.” (Source: Wikipedia). Ultraviolet or UV curing is used to create a photochemical reaction using high intensity Ultraviolet (UV) energy or “light” to quickly dry inks, adhesives or conformal coatings. Most materials cure with a UV wavelength around 350 ~ 400nm although some materials require UVC energy near 255nm. There are many advantages to using UV curing over other traditional methods of curing. Not only will it increase production speed, it assists in creating a better bond, and improves scratch and solvent resistance. When compared to other methods of curing, UV curing generates a more reliable cured product at a much higher rate of production in a considerably shorter period of time....

Publisher: ETS - Energy Technology Systems, Inc.

Improve Crimp Quality to Increase Productivity

Aug 17, 2015 | Pete Doyon, VP, Product Management, Schleuniger, Inc.

Since a high percentage of product failures can be traced to poor electrical connections, crimp quality is of paramount importance. There are many factors that come into play that affect crimp quality and knowing the relevant factors, and to what extent each factor affects the end result, will help to guide the process engineer towards achieving the best possible results. ...

Publisher: Schleuniger, Inc.

Pad Cratering Susceptibility Testing with Acoustic Emission

Aug 13, 2015 | Wong Boon San, Julie Silk; Agilent Technologies | Richard Nordstrom, Ph.D.; Acoustic Technology Group,

Pad cratering has become more prevalent with the switch to lead free solders and lead free compatible laminates. This mainly is due to the use of higher reflow temperature, stiffer Pb-free solder alloys, and the more brittle Pb-free compatible laminates. However, pad cratering is difficult to detect by monitoring electric resistance since pad cratering initiates before an electrical failure occurs.

Several methods have been developed to evaluate laminate materials' resistance to pad cratering. Pad-solder level tests include ball shear, ball pull and pin pull. The detailed methods for ball shear, ball pull, and pin pull testing are documented in an industry standard IPC-9708. Bansal, et al. proposed to use acoustic emission (AE) sensors to detect pad cratering during four-point bend test. Currently there is an industry-working group working on test guidelines for acoustic emission measurement during mechanical testing....

Publisher: Agilent Technologies, Inc.

Enclosed Media Printing as an Alternative to Metal Blades

Aug 06, 2015 | Michael L. Martel

Fine pitch/fine feature solder paste printing in PCB assembly has become increasingly difficult as board geometries have become ever more compact. The printing process itself, traditionally the source of 70% of all assembly defects, finds its process window narrowing. The technology of metal blade squeegees, with the aid of new materials, understanding, and settings such as blade angle, has kept pace with all but the smallest applications, e.g., 200μ - .50 AR and 150μ - .375 AR, which have been pushing blade printing technology to its limits.

Enclosed media print head technology has existed, and has been under increasing development, as an alternative to metal squeegee blade printing. Until recently, the performance of enclosed print heads had been comparable to the very best metal squeegees, but advances in enclosed print media technology have now made it a superior alternative to squeegee blades in virtually all applications....

Publisher: Speedline Technologies, Inc.

5 Axis Fluid Dispensing

Jul 31, 2015 | Brian Stumm

Technology is in constant change and circuit assembly is no different. It is becoming more and more advanced as needs change and demands for more capabilities increase. In order to meet these demands, equipment manufacturers are integrating the latest innovations and tools to serve the industry. The need to better protect printed circuit assemblies from harsh environments using automated selective conformal coating is becoming a must. 5 axis fluid dispensing allows conformal coating to be applied to printed circuit assemblies like never before....

Publisher: ETS - Energy Technology Systems, Inc.

Thermal Curing of Conformal Coatings

Jul 27, 2015 | Wes Noble

When it comes to the application of conformal coating, curing the coating plays a key role in the circuit assembly and selective conformal coating process. Curing conformal coating occurs after the coating spray/dispense process is complete. The coating is considered “cured” when the conformal coating on the circuit assembly is sufficiently tack-free to be handled. Curing can sometimes be accomplished at room temperature but takes a considerable amount of time to dry. Accelerated conformal coating curing decreases this drying period, the cure process reaches either the tack-free or a fully dried state but not quite having fully cured properties. Accelerated curing techniques include one or a combination of heat, moisture, UV light, and chemical reaction curing. This article focuses primarily on thermal or heat curing....

Publisher: ETS - Energy Technology Systems, Inc.

Measuring Conformal Coating Thickness

Jul 21, 2015 | Roger Plough

Achieving an even coat at the right desired thickness is a major challenge when it comes to applying conformal coating to a Printed Circuit Board (PCB). Applying a coating too thin will ultimately render the electronic assembly vulnerable to potential environmental risks therefore defeating the purpose of the coating. Apply the coat too thick, and it could leave the electronic specific components non-functional therefore destroying the electronic assembly entirely. Coating thickness must meet quality specifications. Measurements for coating thickness may be taken while film is dry or wet. Once measurements are recorded, thickness is compared to quality specifications and fluid dispensing automation machinery is calibrated as necessary. There are a handful of methods for measuring conformal coating thickness that are commonly used in the Electronic Manufacturing Services (EMS) and Original Electronic Manufacturer (OEM) industries. A few commonly used methods for checking conformal coating thickness include:...

Publisher: ETS - Energy Technology Systems, Inc.

Testing Printed Circuit Boards for Creep Corrosion in Flowers of Sulfur Chamber

Jul 16, 2015 | Haley Fu; iNEMI, Prabjit Singh, Levi Campbell, Jing Zhang; IBM Corporation, Wallace Ables; Dell Corporation, Dem Lee, Jeffrey Lee; iST-Integrated Service Technology, Jane Li, Solomon Zhang; Lenovo Limited Corporation, Simon Lee; The Dow Chemical Company.

Qualification of electronic hardware from a corrosion resistance standpoint has traditionally relied on stressing the hardware in a variety of environments. Before the development of tests based on mixed flowing gas (MFG), hardware was typically exposed to temperature-humidity cycling. In the pre-1980s era, component feature sizes were relatively large. Corrosion, while it did occur, did not in general degrade reliability. There were rare instances of the data center environments releasing corrosive gases and corroding hardware. One that got a lot of publicity was the corrosion by sulfur-bearing gases given off by data center carpeting. More often, corrosion was due to corrosive flux residues left on as-manufactured printed circuit boards (PCBs) that led to ion migration induced electrical shorting. Ion migration induced failures also occurred inside the PCBs due to poor laminate quality and moisture trapped in the laminate layers....

Publisher: iNEMI (International Electronics Manufacturing Initiative)

What is Kelvin Test?

Jul 14, 2015 | Rick Meraw, Todd Kolmodin, Manfred Ludwig, Holger Kern.

The PCB industry is ever changing and adapting to new technologies. OEM specifications and requirements have also advanced due to these technologies. In some cases the OEMs are asking for a low resistance test to be performed on some or all electrical test nets of the PCB or on the holes of the PCB. This requirement is typically not well defined on the fabrication drawing and that leads to misleading conclusions by the fabrication house (...)

This paper will use the data gathered by the company’s operations to outline what a 4-wire Kelvin test is and how it can be used. Several examples will be illustrated of what the 4 wire Kelvin test can and cannot do. A clear definition of what limitations are present during the testing operation will be defined. The paper will assist designers in understanding how the low resistance test can assist them and also identify causes that can identify unwanted concerns/issues....

Publisher: Gardien Services USA

Reliability Study of Bottom Terminated Components

Jul 14, 2015 | Jennifer Nguyen, Hector Marin, David Geiger, Anwar Mohammed, and Murad Kurwa

Bottom terminated components (BTC) are leadless components where terminations are protectively plated on the underside of the package. They are all slightly different and have different names, such as QFN (quad flat no lead), DFN (dual flat no lead), LGA (land grid array) and MLF (micro lead-frame. BTC assembly has increased rapidly in recent years. This type of package is attractive due to its low cost and good performance like improved signal speeds and enhanced thermal performance.

However, bottom terminated components do not have any leads to absorb the stress and strain on the solder joints. It relies on the correct amount of solder deposited during the assembly process for having a good solder joint quality and reliable reliability. Voiding is typically seen on the BTC solder joint, especially on the thermal pad of the component. Voiding creates a major concern on BTC component’s solder joint reliability. There is no current industry standard on the voiding criteria for bottom terminated component. The impact of voiding on solder joint reliability and the impact of voiding on the heat transfer characteristics at BTC component are not well understood. This paper will present some data to address these concerns....

Publisher: Flex (Flextronics International)

Predicting Fatigue of Solder Joints Subjected to High Number of Power Cycles

Jul 09, 2015 | Craig Hillman, Nathan Blattau, Matt Lacy

Solder joint reliability of SMT components connected to printed circuit boards is well documented. However, much of the testing and data is related to high-strain energy thermal cycling experiments relevant to product qualification testing (i.e., -55C to 125C). Relatively little information is available on low-strain, high-cycle fatigue behavior of solder joints, even though this is increasingly common in a number of applications due to energy savings sleep mode, high variation in bandwidth usage and computational requirements, and normal operational profiles in a number of power supply applications.

In this paper, 2512 chip resistors were subjected to a high (>50,000) number of short duration (<10 min) power cycles. Environmental conditions and relevant material properties were documented and the information was inputted into a number of published solder joint fatigue models. The requirements of each model, its approach (crack growth or damage accumulation) and its relevance to high cycle fatigue are discussed....

Publisher: DfR Solutions (acquired by ANSYS Inc)

Reliability Screening of Lower Melting Point Pb-Free Alloys Containing Bi

Jul 01, 2015 | Joseph M. Juarez, Michael Robinson, Joel Heebink; Honeywell, Polina Snugovsky, Eva Kosiba, Jeffrey Kennedy, Zohreh Bagheri, Subramaniam Suthakaran, Marianne Romansky; Celestica.

Aerospace and military companies continue to exercise RoHS exemptions and to intensively research the long term attachment reliability of RoHS compliant solders. Their products require higher vibration, drop/shock performance, and combined-environment reliability than the conventional SAC305 alloy provides. The NASA-DoD Lead-Free Electronics Project confirmed that pad cratering is one of the dominant failure modes that occur in various board level reliability tests, especially under dynamic loading.

One possible route to improvement of the mechanical and thermo-mechanical properties of solder joints is the use of Pb-free solders with lower process temperatures. Lower temperatures help reduce the possibility of damaging the boards and components, and also may allow for the use of lower Tg board materials which are less prone to pad cratering defects. There are several Sn-Ag-Bi and Sn-Ag-Cu-Bi alloys which melt about 10°C lower than SAC305. The bismuth in these solder compositions not only reduces the melting temperature, but also improves thermo-mechanical behavior. An additional benefit of using Bi-containing solder alloys is the possibility to reduce the propensity to whisker growth...

Publisher: Honeywell International

Return on Investment of a Pre-Reflow AOI System

Jun 30, 2015 | CyberOptics Corporation

This paper describes the losses from defects at the placement process in the SMT line. Two case studies of European and Taiwanese SMT manufacturers illustrate the actual losses from their defects. An evaluation method to select a pre-reflow AOI system maximizing the return on investment (ROI) is introduced. In the end, ROIs of three commercial pre-reflow AOI systems are compared to demonstrate the importance of selecting an appropriate AOI system. This paper will increase the probability that anyone installing an AOI system during the pre-reflow process will obtain a successful gain with short payback period....

Publisher: CyberOptics Corporation

Automated Fluid Dispensing for Epoxy

Jun 30, 2015 | Eric Sari

Robotics for automated fluid dispensing have the ability to apply a variety of materials including epoxy, silicone, and acrylic coatings. These materials are extensively used in today’s high-speed fluid dispensers for the electronics industry.

Whether a dispenser is applying epoxy or another material, the central concept for applying any form of material remains the same. Specific points of an item being dispensed onto are programmed into the dispensing system. The automated fluid dispensers software interprets the programmed information and keeps the travel path in memory. A robotic arm moves fluid dispensing nozzles along this travel path and applies epoxy onto the surface of the item with precise accuracy. Machine speed can be adjusted to emit varying amounts of epoxy. The overall application process is auto-regulating and will not be disrupted....

Publisher: ETS - Energy Technology Systems, Inc.

Reduce labor by automating your Selective Conformal Coating process

Jun 22, 2015 | Brian Stumm, Wes Noble

Applying conformal coatings to electronics has come a long way since the days of manually coating circuit boards. The extreme accuracy and highly repetitive process of automated conformal coatings is moving the electronics industry towards a more defect-free era for conformal coating. It enables new forms of electronics to become better protected, making it possible for electronics to withstand harsher environments than ever before. The following article is meant to aid in clarifying the advantages of specialty coating systems over manual applications for selective conformal coating. ...

Publisher: ETS - Energy Technology Systems, Inc.

PCB Surface Finishes: A General Review

Jun 22, 2015 | Jun Nable, Ph.D., MacDermid Inc. Waterbury, CT

Surface finishing is an integral part of any PCB fabrication. It is generally applied to exposed Cu connectors and conductors on the board. Surface finishing has numerous important functions. It serves as a protective layer for the Cu connectors during storage. The surface finish helps minimize or reduce tarnish of the Cu substrate. Additionally, since it is the layer that comes into contact with other components during assembly, it ensures good solderability between the PCB and the component during assembly. Furthermore after assembly, the finish helps prolong the integrity of the solder joint during use.

A general review of common PCB surface finishes is presented. The advantages and disadvantages of each are discussed and compared. ...

Publisher: MacDermid Inc.

The Use of an Available Color Sensor for Burn-In of LED Products

Jun 18, 2015 | Tom Melly Ph.D.

In the recent past, the Light Emitting Diode (LED) was hailed as the new energy efficient light source that would never have to be replaced. There were claims of 50,000+ hrs lifetime for the humble LED. That story has changed over the last few years as the number and diversity of the LED based products has increased. This is not to say that the original evidence was incorrect, but the initial enthusiastic estimates from the labs did not match the ultimate test, customers. As a result of poor quality products affecting the overall opinion of LED based products, it is critical that manufacturers can be confident in the quality of their product. In current times we want to have products certified, checked and ensure that we have the best quality.

For the purposes of this paper we will look at one aspect of LED product, and this is the Lumen maintenance and estimated lifetime. The method described here does not seek to replace using high quality rating labs, but hopefully will allow the manufacturer to know with confidence that their prototype product, upon going to certification labs will be of a high enough quality that no expensive re-designs are required....

Publisher: Feasa Enterprises Limited

Solder Paste Stencil Design for Optimal QFN Yield and Reliability

Jun 11, 2015 | B. Gumpert

The use of bottom terminated components (BTC) has become widespread, specifically the use of Quad Flat No-lead (QFN) packages. The small outline and low height of this package type, improved electrical and thermal performance relative to older packaging technology, and low cost make the QFN/BTC attractive for many applications.

Over the past 15 years, the implementation of the QFN/BTC package has garnered a great amount of attention due to the assembly and inspection process challenges associated with the package. The difference in solder application parameters between the center pad and the perimeter pads complicates stencil design, and must be given special attention to balance the dissimilar requirements...

Publisher: Lockheed Martin Corporation

Tin Whisker Risk Mitigation for High-Reliability Systems Integrators and Designers

Jun 04, 2015 | David Pinsky, Elizabeth Lambert

Integrators and designers of high-reliability systems exert little or no control over component-level plating processes that affect the propensity for tin whiskering. Challenges of how to assure long-term reliability, while continuing to use COTS parts plated with pure tin, continue to arise.

An integrated, quantitative, standardized methodology is proposed whereby mitigation levels can be selected that are appropriate for specific applications of pure tin for given end-uses. A system of hardware end-use classification is proposed, together with recommended appropriate risk mitigation approaches. An updated version of the application-specific risk assessment algorithm is presented together with recommended thresholds for acceptability within the context of the hardware classifications....

Publisher: Raytheon

Beyond 0402M Placement: Process Considerations for 03015M Microchip Mounting

May 28, 2015 | Brent Fischthal, Sr. Marketing Manager, Products & Solutions Michael Cieslinski, Engineering Manager Panasonic Factory Solutions Company of America.

The printed circuit board assembly industry has long embraced the "Smaller, Lighter, Faster" mantra for electronic devices, especially in our ubiquitous mobile devices. As manufacturers increase smart phone functionality and capability, designers must adopt smaller components to facilitate high-density packaging. Measuring over 40% smaller than today's 0402M (0.4mmx0.2mm) microchip, the new 03015M (0.3mm×0.15mm) microchip epitomizes the bleeding-edge of surface mount component miniaturization.

This presentation will explore board and component trends, and then delve into three critical areas for successful 03015M adoption: placement equipment, assembly materials, and process controls. Beyond machine requirements, the importance of taping specifications, component shape, solder fillet, spacing gap, and stencil design are explored. We will also examine how Adaptive Process Control can increase production yields and reduce defects by placing components to solder position rather than pad. Understanding the process considerations for 03015M component mounting today will help designers and manufacturers transition to successful placement tomorrow....

Publisher: Panasonic Factory Solutions Company of America (PFSA)

“A New Paradigm in Crimping Press Design” By Rob Boyd, Senior Product Manager, Schleuniger, Inc.

May 27, 2015 | Rob Boyd, Senior Product Manager, Schleuniger. Inc.

It goes without saying that manufacturing companies want the highest possible quality at the lowest possible cost. These days, everyone is trying to do more with less in order to stay relevant in a competitive environment....

Publisher: Schleuniger, Inc.