defect of the month
Dendrites on PCB Assemblies
Solder joint corrosion causes.
This month we illustrate dendrites and corrosion on board assemblies. The example in FIGURE 1 is straightforward. Saltwater was found on the surface of the metal board. It caused intermittent operation of the LED before failure at 25 meters. Yes, you guessed it: My underwater light leaked due to a rubber gasket failure. The rubber had been out in the sun too long and hardened, then cracked. The image shows chemical reaction with dendrite formation on the surface of the joints and some green verdigris.

FIGURE 2 is a dendrite under a component that caused intermittent failure. This was the result of not evaluating a new solder paste correctly after a change in solder paste supplier, plus a failure to change the reflow profile.

We have presented live process defect clinics at exhibitions all over the world. Many of our Defect of the Month videos are available online at youtube.com/user/mrbobwillis.

Figure 1: LED corrosion
Figure 1. LED corrosion.
Figure 2: X-ray of dendrite.
Figure 2. X-ray of dendrite.
Bob Willis illustration
Bob Willis
is a process engineering consultant; bob@bobwillis.co.uk. His column appears monthly.