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SMTnet Express, October 5, 2023, Subscribers: 25,109, Companies: 11,903, Users: 28,396

█ Electronics Manufacturing Technical Articles

Effect of Multiple Reflow Cycles on Intermetallic Compound Creation

This paper deals with the effect of the solder profile and multiple reflow cycles on intermetallic compound (IMC) creation. Soldered joints between PCB and 1206 size chip resistors were made from SAC 305 or SnBi solder alloy. Samples were reflowed one to six times with one of the two different soldering profiles for each soldering alloys. The thickness and composition of IMC layers were measured and observed with a scanning electron microscope. The growing of IMC layers thickness was observed. The results are presented depending on greater value of heating factor and number of reflow cycles. The shear forces for the components were measured and the fracture interfaces were inspected.

Credit: University of West Bohemia

Intermetallic Growth in Tin-Rich Solders

For tin-rich solder alloys, 200 C (392 F) is an extreme temperature. Intermetallic growth in tin-copper systems is known to occur and is believed to bear a direct relationship to failure mechanisms. This study of morphological changes with time at elevated temperatures was made to determine growth rates of tin-copper intermetallics. Preferred growth directions, rates of thickening, and notable changes in morphology were observed.

Each of four tin-base alloys was flowed on copper and exposed to temperatures between 100 C and 200 C for time periods of up to 32 days. Metallographic sections were taken and the intermetallics were examined. Intermetallic layer thickening is characterized by several distinct stages. The initial growth of side plates is extremely rapid and exaggerated. This is followed by retrogression (spheroidization) of the elongated peaks and by general thick-

Credit: General Electric

Effect of Cooling Rate on the Intermetallic Layer in Solder Joints

While it has long been known that the Cu6Sn5 intermetallic that plays a critical role in the reliability of solder joints made with tin-containing alloys on copper substrates exists in two different crystal forms over the temperature range to which electronics circuitry is exposed during assembly and service, it has only recently been recognized that the change from one form to the other has implications for solder joint reliability. (..) In this paper the authors report a study of the effect of cooling rates on Cu6Sn5 crystals. Cooling rates from 200°C ranged from 10°C/minute to 100°C/minute and the effect of isothermal ageing at intermediate temperatures was also studied. The extent of the phase transformation after each regime was determined using synchrotron X-ray diffraction. The findings have important implications for the manufacture of solder joints and their in-service performance... First published in the 2012 IPC APEX EXPO technical conference proceedings....

Credit: Nihon Superior Co., Ltd.

Effect of Gold Content on the Microstructural Evolution of SAC305 Solder Joints Under Isothermal Aging

Au over Ni on Cu is a widely used printed circuit board (PCB) surface finish, under bump metallization (UBM), and component lead metallization. It is generally accepted that less than 3 wt.% Au in Sn-Pb solder joints inhibits formation of detrimental intermetallic compounds (IMC). However, the critical limit for Au content in Pb-free solder joints is not well established. Three surface-mount package platforms, one with a matte Sn surface finish and the others with Ni/Au finish, were soldered to Ni/Au-finished PCB using Sn-3.0Ag 0.5Cu (SAC305) solder, in a realistic manufacturing setting. The assembled boards were divided into three groups: one without any thermal treatment, one subjected to isothermal aging at 125°C for 30 days, and the third group aged at 125°C for 56 days...

Credit: Agilent Technologies, Inc.

Solder Joint Reliability Under Realistic Service Conditions

The ultimate life of a microelectronics component is often limited by failure of a solder joint due to crack growth through the laminate under a contact pad (cratering), through the intermetallic bond to the pad, or through the solder itself. Whatever the failure mode proper assessments or even relative comparisons of life in service are not possible based on accelerated testing with fixed amplitudes, or random vibration testing, alone. Effects of thermal cycling enhanced precipitate coarsening on the deformation properties can be accounted for by microstructurally adaptive constitutive relations, but separate effects on the rate of recrystallization lead to a break-down in common damage accumulation laws such as Miner's rule. Isothermal cycling of individual solder joints revealed additional effects of amplitude variations on the deformation properties that cannot currently be accounted for directly.

We propose a practical modification to Miner's rule for solder failure to circumvent this problem. Testing of individual solder pads, eliminating effects of the solder properties, still showed variations in cycling amplitude to systematically reduce subsequent acceleration factors for solder pad cratering. General trends, anticipated consequences and remaining research needs are discussed

Credit: Universal Instruments Corporation

SEE Forum results for related keywords - "intermetallic" (408)

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█ Printed Circuit Board Assembly & PCB Design Forum

Cleaning PCBs with a MEMS microphone on it -- Hey folks, I have a few designs that I'm using a MEMS I2S microphone on, and the PCBs have to be cleaned as I use water based SAC305 - but the supplier states to NOT ultrasonically clean their microphones. Has anyone here been through the process of using and having to clean "un-cleanable" MEMS devices on their boards and found a solution? Is it enough to cover the Mic hole with some kapton tape before cleaning (assuming the agitation doesn't make the tape come off) ? Surely there must be a way to reduce damage to the parts when cleaning. Changing to a no-clean paste is not an option, so I need to find a way to get these parts usable in my product/manufacturing requirements. Thanks in advance! Seon - Unexpected Maker

Water after PCB batch wash -- I've been looking for information on how, if at all, any of you treat water after a pcb batch wash. In particular, we have a Trident LD machine, using Zestron cleaning chemical. We have a carbon tank and two mixed bed media tanks as well as two 5 micron filters we use before discharging to city sewer. Is anyone else using this much filtration, or are we overkill and can cut back? Between the filtering service and DI system, we go through a lot. I've already talked with the city and DNR with water discharge, and since we don't manufacture PCB's, we only assemble, they don't have specific standards for us.

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In the previous 12 months, the number of threads opened on the FORUM seeking your help was: 288	ADD thoughts to the Assembly Forum ...

█ SMT, PCB Electronics Assembly Manufacturing Industry News

FKN Systek Provides Blade Resharpening for PCB Depanelizers Re-sharpening blades is one way to get the most mileage out your equipment... FKN Systek
Nihon Superior's Mr. Keith Sweatman to Present at the 2023 SMTA International Technical Conference Nihon Superior Co. Ltd. is pleased to announce that Keith Sweatman, the company's Senior Technical Advisor, will deliver a presentation titled "A Path to Ductile Low-Temperature Solders for Mass Production of Electronic Assemblies" at the upcoming SMTA International conference and exposition. This prestigious event is scheduled to take place Oct. 9-12, 2023 at the Minneapolis Convention Center in Minneapolis, MN. Keith Sweatman's presentation is scheduled within session LTS4, titled "Effects of Elemental Additions to Sn-Bi solder Alloys," and will take place on Thursday, Oct. 12, 2023, from 8:30 to 10:00 a.m.... Nihon Superior Co., Ltd.
2023 Stromberg Student Leader Scholarship Recipient Announced SMTA is pleased to announce Catherine Wong, Foothill College, has been selected as the recipient of the 2023 JoAnn Stromberg Student Leader Scholarship.... Surface Mount Technology Association (SMTA)

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█ SMT / PCB Products & Services

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I.C.T AOI Solution

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Pillarhouse Jade Handex

Pillarhouse USA

Inspection

CameraLink High Resolution Industrial Cameras

ISVI - Industrial Sensor Vision International Corporation

Software

Unisoft ProntoAOI - AOI Machines Programming Software

UNISOFT Corporation

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█ Electronic Equipment Mart

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█ Electronics Manufacturing & Assembly Events Calendar

EVENTS

SMTA International Conference & Exposition | October 9 to 12

SMTA

█ Electronics Manufacturing Training Courses & PCB Assembly Training

FIND TRAINING FOR:

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TRAINING - Electronics Manufacturing and PCB Assembly Training Courses

IDEA-STD-1010 Essentials Online Live Training Course

Multiple dates and locations. Check the link for details

EPTAC Corporation

Idea Counterfeit Component Workshop Online Live Training

Multiple dates and locations. Check the link for details

EPTAC Corporation

Component Identification Online Live Certification

Multiple dates and locations. Check the link for details

EPTAC Corporation

TRAINING - PCB Inspection Electronics Manufacturing Training Courses

IPC-A-640 Interactive PCB Inspection Lab (CIT or CIS Option)

Multiple dates and locations. Check the link for details

EPTAC Corporation

TRAINING - PCB Rework and Hand Soldering Training Courses

Customizable Basic Hand Soldering

Multiple dates and locations. Check the link for details

Blackfox Training Institute, LLC

TRAINING - Online Electronics Manufacturing and Assembly Training Courses

Reflow Soldering 101 Training Course

Surface Mount Technology Association (SMTA)

IPC/WHMA-A-620 Expert (CSE) Certification Training Course

EPTAC Corporation

IPC Certified Electronics Program Manager (CEPM) Training and Certification Program

Association Connecting Electronics Industries (IPC)

Component Placement 101 Training Course

Surface Mount Technology Association (SMTA)

ESD Control for Electronics Assembly

Association Connecting Electronics Industries (IPC)

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█ Electronics Manufacturing & PCB Assembly Jobs

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Golden, CO, USA

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Williamsport, Pennsylvania, USA

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Williamsport, Pennsylvania, USA

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Williamsport, Pennsylvania, USA

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Williamsport, Pennsylvania, USA

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Williamsport, Pennsylvania, USA

Spartronics

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Brooksville, Florida, USA

Spartronics

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Spartronics

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Williamsport, Pennsylvania, USA

Spartronics

RESUMES - POST your resume now

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█ PCB Design & Assembly Industry Associations

Surface Mount Technology Association (SMTA)

SMTA is a non-profit international association of companies and individuals (totalling 4,000) involved in all aspects of advanced electronics assembly, surface mount and related technologies.

Membership Info | SMTA Certification | Bookstore | Upcoming Events

Association Connecting Electronics Industries (IPC)

IPC is a US-based trade association dedicated to the competitive excellence and financial success of its nearly 2,600 member companies which represent all facets of the electronic interconnection industry, including design, printed wiring board manufacturing and electronics assembly.

Membership Info | Training & Certification | Online Store | Upcoming Events

Editor - Dave "davef" Fish (submit your technical articles)

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