Solder Joint Opens - What To Do?

 

Electronic components are soldered to circuit boards every day and in some cases opens are found during x-ray inspection or during the test. You may be inclined to re-heat and reflow the solder using a little extra flux. It's reasonable to think this will work but it can be deflating when it is not effective.

In a desperate attempt to correct the defect, the process may be repeated at higher temperatures or for a longer cycle. Yet again, the opens may remain.

While attempts at secondary reflow may often work successfully, it will not work when there are pads with high levels of oxidation. The only way to reliably rework this type of defective solder joint is to remove the component, condition the pads by removing the oxidation followed by tinning, and finally reinstalling the component.

Partially wetted pads.

Multiple heat cycles not only overheat the components, but also overheat the pads and soldermask, especially when higher lead-free solder temperatures are required. Adjacent components and solder joints can also be impacted negatively.

Damage to component packaging, fractured solder joints, and base board discoloration are some common side effects. It is a perplexing situation. Ask anyone who has pressed down on a component with an open to see it function properly but then when the pressure is removed, the open returns.

The best practice after the first attempt at secondary reflow is to either remove the component and investigate the situation or send the circuit board to a specialist for rework.

Several members of the Circuit Technology Center team contributed to this feature story.

http://www.circuitrework.com/features/825.shtml