Defect of the Month

Bob Willis

Measuring BGA joints can reveal process problems.

This month we show variation in the size of the solder joints on a section of a BGA. Measuring variation on solder ball size after reflow is useful. Even better is when measurements are taken automatically with an x-ray system, as this provides a good comparison tool between NPI and production builds.

Measuring NPI build, and saving the measurement data, provides a good point of reference when problems are seen on a build. It is also useful when moving between contractors or in the event of changes due to other process modifications.

Read more: What Solder Ball Size Variation Can Tell Us

Bob Willis

While coatings are typically used on boards, some choose to coat components as well.

This month we show manual conformal coating on one component. One optical example is shown under normal lighting and then under UV light, to show the tracer added in coatings to allow easy manual or automatic inspection. This is not a defect. I asked if this was intended, however, as it was unusual.

Traditionally, coatings are used to protect circuit boards in humid environments and more so in condensing conditions to prevent corrosion. On some occasions design engineers also use coatings to provide that little stability.

 

Read more: Conformally Coated Chip Caps

Bob WillisInappropriately sized pads can result in excessive solder and, eventually, defects.

This month we show soldering of 01005 chip resistors from an early project with lead-free assembly. The microsection image in FIGURE 1 shows a few issues, but it’s the circles in both joints that caught my eye. Yes, they are voids before they are unmasked. During sectioning we stopped just before entering the void. Most would have continued a few more micros to remove the thin sliver of solder, which was the wall of the void, to show the void. But everyone has seen voids before!

Read more: 01005 Termination Lift

Bob WillisA lack of compression can be seen nondestructively.

This month we look at crimp connections.

FIGURES 1 and 2 show examples of simple compression connections. Figure 1 shows an excessive length of stripped wire within the crimp termination and a total lack of any compression, which should be easy to see on the wire bundle from the point of entry to the point of compression. Figure 2 lacks compression of the connector, and the stripped wire is barely within the barrel of the connector.

Read more: Incomplete Crimp Connections

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