Printed Circuit Design & Fab Online Magazine - Current Issue

Current Issue

Dr. Chris Hunt
When joints look perfect but nonetheless are failing, check the plating adhesion.

Exposed copper coupled with silver final finish is causing opens.

Figures 1 and 2 show two images of the same problem: one x-ray, the other optical. In both cases it’s the result of sulphur corrosion on the surface of copper and silver surfaces. Both surfaces remain exposed after a soldering operation, and in the presence of sulphur, it is possible to witness corrosion. In time it can result in an open connection, as the figures show. Figure 1, taken on a Dage x-ray system, shows different degrees of corrosion on the tracking just below the solder joint fillet. In failure investigations it’s important to see and record as much as possible without change or damage to the sample. On one joint there was an open connection on this QFP device.

Read more: Sulphur Corrosion on Solder Joints

John Burkhert, Jr. Effective PCB testing depends on balancing electrical validation with manufacturable design practices throughout product development.

“Don’t get testy with me.” People might say those words when they’re annoyed by a challenging statement. The point of testing is to challenge assumptions. It’s the “find out” phase of product development. Printed circuit boards benefit from testing at multiple stages of production. Let’s dive into the deep end.

Read more: Printed Circuit Board Design for Test

John Burkhert, Jr. Connector selection and footprint design require careful DfM consideration, as tolerances, spacing and assembly constraints directly impact manufacturability and performance.

When it comes to interconnects for printed circuit boards, I found one vendor with 25,217 options. A specialty vendor offered only about 9,000 different connector SKUs. Luckily, connector selection can typically be narrowed by pin count, pitch and other key parameters.

Read more: A Guide to PCB Connectors: Selection, Design and DfM Tips