Defects Database

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

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Dr. Chris Hunt
Exhausted flux can cause incomplete reflow.

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Dr. Chris Hunt

A lack of flux or dip paste on the package can lead to post-reflow defects.
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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.

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It depends not just on where one looks, but when.

Are these open connections, non-reflow or good quality control? It all depends on which stage of the process the product is in when inspected.

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One culprit could be package warping.

Figure 1 shows the Amkor TMV package after microsectioning the board assembly during failure analysis. This particular view shows open joints between the top package and the solder spheres on the bottom package.

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