Technical Library | 2014-09-11 11:47:39.0
This article goes through the pluses and minuses of using plastic stencils for DIY prototypes. The release efficiency is measured and "rules of thumb" for using one type vs another is explained.
Technical Library | 2013-07-03 10:31:54.0
It has been demonstrated in numerous pieces of work that stencil printing, one of the most complex PCB assembly processes, is one of the largest contributors to defects (Revelino et el). This complexity extends to prototype builds where a small number of boards need to be assembled quickly and reliably. Stencil printing is becoming increasingly challenging as packages shrink in size, increase in lead count and require closer lead spacing (finer pitch). Prototype SMT assembly can be further divided between industrial and commercial work and the DIYer, hobbyist or researcher groups. This second group is highly price sensitive when it comes to the materials used for the board assembly as their funds are sourced from personal or research monies as opposed to company funds. This has led to development of a lower cost SMT printing stencil made from plastic film as opposed to the more traditional stainless steel stencil used by industrial and commercial users.This study compares the performance of these two traditional materials and their respective impact on solder paste printing including efficiency and print quality.
Technical Library | 2013-01-11 16:51:33.0
There have been claims in the industry that laser-cut electroformed nickel foil blanks provide stencil print performance comparable to electroformed stencils. A study was established to measure the quantitative differences in performance between the two during an independent lab study.
Technical Library | 2016-08-04 14:33:23.0
Solder paste screen printing is known to be one of the most difficult processes to quality assure in Printed Board Assembly (PBA) manufacturing. An important process step in solder paste screen printing is the under stencil cleaning process and one of the key materials in this process is the cleaning paper1. This, often neglected, material affects the cleaning process and thereby also the print quality. It is therefore important to perform tests of different cleaning papers before one could be chosen. This article describes how cleaning papers can be tested and it also tells how big differences it can be between different materials.
Technical Library | 2009-09-09 15:08:19.0
Stencil printing equipment has traditionally been used in the surface mount assembly industry for solder paste printing. In recent years the flexibility of the tool has been exploited for a wide range of materials and processes to aid semiconductor packaging and assembly. One such application has been the deposition of adhesive coatings onto the backside of silicon wafers.
Technical Library | 2018-03-28 14:54:36.0
Six decades of legacy experience makes the specification and production of screens and masks to produce repeatable precision results mostly an exercise in matching engineering needs with known ink and substrate performance to specify screen and stencil characteristics. New types of functional and electronic devices, flex circuits and medical sensors, industrial printing, ever finer circuit pitch, downstream additive manufacturing processes coupled with new substrates and inks that are not optimized for the rheological, mechanical and chemical characteristics for the screen printing process are becoming a customer driven norm. Many of these materials do not work within legacy screen making, curing or press set-up parameters. Many new materials and end uses require new screen specifications.This case study presents a DOE based method to pre-test new materials to categorize ink and substrate rheology, compatibility and printed feature requirement to allow more accurate screen recipes and on-press setting expectations before the project enters the production environment where time and materials are most costly and on-press adjustment methods may be constrained by locked, documented or regulatory processes, equipment limitations and employee experience.
Technical Library | 2014-12-24 19:22:52.0
For centuries, the squeegee blade has been used throughout many applications for depositing viscous materials through screens and stencils to transfer images on to substrates, from cloth material to electronic circuit boards. One area of blade printing mechanics that have been reviewed many times is the angle of attack of the blade. Typically it has been tested from 45 degrees to 60 degrees to optimize the printing quality and efficiency. However, this typically ends up as a compromise, from fill characteristics (45 degrees) to print definition (60 degrees). This paper will present the revolutionary performance of the profiled squeegee blade, which has recently been developed to create a virtual multi angle of attack for unsurpassed process control for all types of stencil printing processes.
Technical Library | 2018-03-15 07:23:35.0
The SMT assembly process is continuously challenged by the factors which enhance circuit board performance and limit productivity. The pick and place and reflow systems reflect these driven issues by adding more and more controls to their systems, but the fact is one of the age old processes continues to operate within the same rules since the dawn of the SMT assembly world: The SMT screen printing. (...)This paper showcases a new stencil process that was discovered by reverting to the basics:understanding the reason for each stencil material process, focusing on detailed finishes and a disciplined aperture design process, maintaining original designs, and making the correctly designed apertures to control the paste deposition. The test results drove us to focus the efforts on the aperture walls In this paper we will demonstrate with lab tests SMT process results howthe improved paste release results in improved SMT print process performance and its positive impact on SPI yields and EOL performance.
Technical Library | 2007-12-13 17:03:02.0
Printer-hosted processes for solder ball placement are now widely used for package technologies ranging from BGAs using ball diameters above 750μm to the latest WL-CSPs demanding 250μm diameter. This broadening spectrum of applications brings more choices in terms of stencil design rules and production methodologies.
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.
