Technical Library | 2013-06-20 14:33:12.0
With today's consumer technologies driving the need for denser and more compact devices, the assembly process for surface mounted devices has becoming increasingly more difficult. With the mixture of components requiring a broader range of print deposition volume, various techniques are in use in an attempt to ensure consistent and appropriate paste volume is achieved. Some of these techniques include step etching a stencil locally on a targeted device, promoting electroformed smooth wall nickel stencils, through to laser cutting newer grade stencil materials. This paper focuses on the relevant attributes that affect the properties of solder paste release and introduces the effects of surface free energy with respect to key elements that make up the stencil printing process.
Technical Library | 2012-10-25 16:34:02.0
First published in the 2012 IPC APEX EXPO technical conference proceedings. This paper will examine stencil technologies (including Laser and Electroform), Aperture Wall coatings (including Nickel-Teflon coatings and Nano-coatings), and how these parameters influence paste transfer for miniature devices with Area Ratios less than the standard recommended lower limit of .5. A matrix of print tests will be utilized to compare paste transfer and measure the effectiveness of the different stencil configurations. Area Ratios ranging from .32 to .68 will be investigated.
Technical Library | 2017-09-28 16:36:33.0
These nano-coatings also refine the solder paste brick shape giving improved print definition. These two benefits combine to help the solder paste printing process produce an adequate amount of solder paste in the correct position on the circuit board pads. Today, stencil aperture area ratios from 0.66 down to 0.40 are commonly used and make paste printing a challenge. This paper presents data on small area ratio printing for component designs including 01005 Imperial (0402 metric) and smaller 03015 metric and 0201 metric chip components and 0.3 mm and 0.4 mm pitch micro BGAs.
Technical Library | 2018-06-13 11:42:00.0
The art of screen printing solder paste for the surface mount community has been discussed and presented for several decades. However, the impending introduction of passive Metric 0201 devices has reopened the need to re-evaluate the printing process and the influence of stencil architecture. The impact of introducing apertures with architectural dimensions’ sub 150um whilst accommodating the requirements of the standard suite of surface mount connectors, passives and integrated circuits will require a greater knowledge of the solder paste printing process.The dilemma of including the next generation of surface mount devices into this new heterogeneous environment will create area ratio challenges that fall below todays 0.5 threshold. Within this paper the issues of printing challenging area ratio and their associated aspect ratio will be investigated. The findings will be considered against the next generation of surface mount devices.
Technical Library | 2023-05-22 16:42:56.0
Nano-coatings are applied to solder paste stencils with the intent of improving the solder paste printing process. Do they really make a noticeable improvement? The effect of Nano-coatings on solder paste print performance was investigated. Transfer efficiencies were studied across aperture sizes ranging from 0.30 to 0.80 area ratio. Also investigated were the effects of Nano-coatings on transfer efficiencies of tin-lead, lead-free, water soluble, no-clean, and type 3, 4, and 5 solder pastes. Solder paste print performance for each Nano-coating was summarized with respect to all of these variables.
Technical Library | 2021-11-17 18:53:50.0
The demand for product miniaturization, especially in the handheld device area, continues to challenge the board assembly industry. The desire to incorporate more functionality while making the product smaller continues to push board design to its limit. It is not uncommon to find boards with castle-like components right next to miniature components. This type of board poses a special challenge to the board assemblers as it requires a wide range of paste volume to satisfy both small and large components. One way to address the printing challenge is to use creative stencil design to meet the solder paste requirement for both large and small components. ... The most important attribute of a stencil is its release characteristic. In other words, how well the paste releases from the aperture. The paste release, in turn, depends on the surface characteristics of the aperture wall and stencil foil. The recent introduction of new technology, nano-coating for both stencil and squeegee blades, has drawn the attention of many researchers. As the name implies, nano-coated stencils and blades are made by a conventional method such as laser-cut or electroformed then coated with nano-functional material to alter the surface characteristics. This study will evaluate nano-coated stencils for passive component printing, including 01005.
Technical Library | 2023-07-25 16:42:54.0
Printing solder paste for very small components like .3mm pitch CSP's and 01005 Chip Components is a challenge for the printing process when other larger components like RF shields, SMT Connectors, and large chip or resistor components are also present on the PCB. The smaller components require a stencil thickness typically of 3 mils (75u) to keep the Area Ratio greater than .55 for good paste transfer efficiency. The larger components require either more solder paste height or volume, thus a stencil thickness in the range of 4 to 5 mils (100 to 125u). This paper will explore two stencil solutions to solve this dilemma. The first is a "Two Print Stencil" option where the small component apertures are printed with a thin stencil and the larger components with a thicker stencil with relief pockets for the first print. Successful prints with Keep-Outs as small as 15 mils (400u) will be demonstrated. The second solution is a stencil technology that will provide good paste transfer efficiency for Area Ratio's below .5. In this case a thicker stencil can be utilized to print all components. Paste transfer results for several different stencil types including Laser-Cut Fine Grain stainless steel, Laser-Cut stainless steel with and w/o PTFE Teflon coating, AMTX E-FAB with and w/o PTFE coating for Area Ratios ranging from .4 up to .69.
Technical Library | 2020-10-27 02:02:17.0
Solder powder size is a popular topic in the electronics industry due to the continuing trend of miniaturization of electronics. The question commonly asked is "when should we switch from Type 3 to a smaller solder powder?" Solder powder size is usually chosen based on the printing requirements for the solder paste. It is common practice to use IPC Type 4 or 5 solder powders for stencil designs that include area ratios below the recommended IPC limit of 0.66. The effects of solder powder size on printability of solder paste have been well documented. The size of the solder powder affects the performance of the solder paste in other ways. Shelf life, stencil life, reflow performance, voiding behavior, and reactivity / stability are all affected by solder powder size. Testing was conducted to measure each of these solder paste performance attributes for IPC Type 3, Type 4, Type 5 and Type 6 SAC305 solder powders in both water soluble and no clean solder pastes. The performance data for each size of solder powder in each solder paste flux was quantified and summarized. Guidance for choosing the optimal size of solder powder is given based on the results of this study.
Technical Library | 2013-02-07 17:01:46.0
Silicone contamination is known to have a negative impact on assembly processes such as soldering, adhesive bonding, coating, and wire bonding. In particular, silicone is known to cause de-wetting of materials from surfaces and can result in adhesive failures. There are many sources for silicone contamination with common sources being mold releases or lubricants on manufacturing tools, offgassing during cure of silicone paste adhesives, and residue from pressure sensitive tape. This effort addresses silicone contamination by quantifying adhesive effects under known silicone contaminations. The first step in this effort identified an FT-IR spectroscopic detection limit for surface silicone utilizing the area under the 1263 cm-1 (Si-CH3) absorbance peak as a function of concentration (µg/cm2). The next step was to pre-contaminate surfaces with known concentrations of silicone oil and assess the effects on surface wetting and adhesion. This information will be used to establish guidelines for silicone contamination in different manufacturing areas within Harris Corporation... First published in the 2012 IPC APEX EXPO technical conference proceedings.
Technical Library | 2020-10-08 00:55:22.0
This article presents the development of a stretchable sensor network with high signal-to-noise ratio and measurement accuracy for real-time distributed sensing and remote monitoring. The described sensor network was designed as an island-and-serpentine type network comprising a grid of sensor "islands" connected by interconnecting "serpentines." A novel high-yield manufacturing process was developed to fabricate networks on recyclable 4-inch wafers at a low cost. The resulting stretched sensor network has 17 distributed and functionalized sensing nodes with low tolerance and high resolution. The sensor network includes Piezoelectric (PZT), Strain Gauge(SG), and Resistive Temperature Detector (RTD) sensors. The design and development of a flexible frame with signal conditioning, data acquisition, and wireless data transmission electronics for the stretchable sensor network are also presented. The primary purpose of the frame subsystem is to convert sensor signals into meaningful data, which are displayed in real-time for an end-user to view and analyze. The challenges and demonstrated successes in developing this new system are demonstrated, including (a) developing separate signal conditioning circuitry and components for all three sensor types (b) enabling simultaneous sampling for PZT sensors for impact detection and (c)configuration of firmware/software for correct system operation. The network was expanded with an in-house developed automated stretch machine to expand it to cover the desired area. The released and stretched network was laminated into an aerospace composite wing with edge-mount electronics for signal conditioning, processing, power, and wireless communication.
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