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.
|Non wetted pads due to heavy oxidation.|
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.
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.
|Partially wetted pads.|
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.