The Reliability Factor in Solder Paste Printing

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Knoll Evangelista is the director of the EMS Components and Group Operations of Laguna, Philippines-based electronics manufacturing services firm EMS Components Assembly Inc.

With more than 25 years in the electronics assembly industry, Evangelista has seen the evolution of the soldering process—from adhesive component mounting with the solder wave machines to screen printing with reflow ovens. He had also set up over 35 SMT lines for high volume production of products ranging from storage devices, consumer electronics, automotive electronics, and medical devices.

In an interview with SMT Magazine, Evangelista speaks about the solder paste printing challenge, what factors impact the process, and best practices to consider.

Stephen Las Marias: From your perspective, what are the biggest challenges when it comes to solder paste printing?

Knoll Evangelista: Reliability of solder joints in electronic products is the biggest challenge, and it depends on the following factors: stencil printing and quality of reflow soldering.

Las Marias: How does the solder paste material impact the process?

Evangelista: The size of the solder paste granules has an impact on the process as it depends on components to be mounted. The pitch distance of ICs, the ball array size, and the distance of BGAs have to be considered in selecting the solder paste material.

Las Marias: How do the tighter tolerances and even narrower PCB lines and spacing affect the solder paste printing process?

Evangelista: More than 50% of defects in assembly of printed circuit boards are attributed to the solder paste printing process. The volume of paste deposit during screen printing is a big factor impacting the quality of solder joints. It requires design of experiments (DOE) to get the right parameters of screen printing machine. It also involves optical inspection to measure the volume of paste deposit to assure consistency of paste application.

The surface mount components such as chip scale packages (CSP), fine pitch BGAs are the challenges in stencil printing and reflow profiling capabilities. Due to tighter tolerances, 3D X-ray inspection is required, which offers capabilities beyond those of microscopes and naked eye.

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Editor's Note: This article originally appeared in the June 2016 issue of SMT Magazine.



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