Electroformed Stencils


Reading time ( words)

The continued drive in electronics to place increasingly smaller components on boards poses continuing challenges to board manufacturers. Tight pad spacing as well as placement of small 0201 and 01005 components is becoming more commonplace on board assemblies. Not only are the parts nearly invisible when placed, but their small size causes challenges with the solder paste application and release needed to yield reproducible, low-defect solder joints. The short scoop this month is that you can meet the challenges of paste application for difficult assembly printing processes by using electroformed stencils. 

It may seem that a stencil is a rather simple device; after all, in its basic form it is just a sheet of metal stretched taught with hole patterns placed in it to allow application of solder paste in the open areas. The stencil and its fabrication have a great influence over the ability of the circuit board assembly manufacturer to reliably reproduce the desired depositions necessary for paste application.

Stencils can be laser cut with or without post-processing, which for many applications is sufficient to get the paste application process completed reliably. Both of these fabrication techniques are currently employed in mainstream stencil production, but they both start to exhibit their limitations as pattern features decrease in size. The roughness of the stencil wall is one of the major influences on how well paste will release from the stencil. The rougher the sidewall of the aperture, the more the paste is prone to sticking onto the edge of the wall. The apertures used with larger pad features are somewhat more tolerant to edge roughness due to usually higher area ratios. As the pattern features decrease in size, the amount of paste that does not release due to a rough edge becomes an increasingly larger portion of the target application volume. So as feature size decreases, the fabrication of the stencil needs to be constructed for enhanced release capability. 

Read the full column here.


Editor's Note: This column originally appeared in the January 2014 issue of SMT Magazine.

Share

Print


Suggested Items

Solder Paste Printing From the Stencil’s Perspective

02/19/2020 | I-Connect007 Editorial Team
Jeff Schake of ASM Assembly Systems discusses the complications surrounding printing and solder paste that he sees from his perspective as a stencil expert.

Blackfox Trains Veterans for Good Manufacturing Jobs

02/18/2020 | Real Time with...IPC
Blackfox Training Institute has been training manufacturing technologists for over 20 years. Based in Longmont, Colorado, Blackfox is now focused on helping veterans of our armed services transition into good jobs in the manufacturing sector. During IPC APEX EXPO 2020, Editor Nolan Johnson spoke with Blackfox CEO Al Dill about the company's veteran training programs, and how this effort is helping companies fill jobs that might otherwise go unfilled.

Solder in PCBA: Can’t Live Without It... or Can We?

02/17/2020 | Joe Fjelstad, Verdant Electronics
For most of its historical use in electronics, the solder alloy of choice was tin-lead, either an Sn60/Pb40 alloy or the Sn63/ Pb37 eutectic version of the tin-lead alloy. These two alloys were the workhorses of the industry. They were both well understood in terms of their processing and reliability—that is, until the advent of lead-free, a well-meaning but ill-conceived and poorly executed conversion, forced on the industry by the European Union in 2006.



Copyright © 2020 I-Connect007. All rights reserved.