|Ask the Experts|
August 7, 2020
Old Components and Blow Holes
Are old components such as resistors and circuit breakers more likely to cause blow holes during wave soldering compared to new components?
|Expert Panel Responses|
Blow holes are primarily the result of poor hole wall generation of the PWB and defective or insufficient plating thickness. Some components can outgas during assembly but again it is a function of poor plating quality regardless of age.
Bottom line, old components will not increase blow hole defects but you could have an increase in process voiding in the solder joints due to poor solderability of the older devices.
S T and S Testing and Analysis
I can certainly see old components causing wetting problems. If the wetting problems are spotty, localized issues and some happen to be near the fillet on the solder destination side, then they could look potentially look a little like there had been some outgassing.
If you feel that the defects are classic blowholes, then I'd say the source is very likely not the components but the PWB. The only way to be sure is to substitute a new lot of parts for a particular part that has been showing a lot of the defect in question, and see if the issue goes away. Now go back to the old parts. Does it come back? If you can turn it off and on, you know you are getting a handle on it.
The best way to identify the cause is with a cross section of the circuit board joints exhibiting the problem.
Blow holes are the result of moisture/liquid trapped behind the plating of the plated through holes expanding to form gas, building enough pressure to break through the plated through hole wall and expanding into the solder joint. The cause is dull drill bits that did not give clean holes in the circuit board before plating.
Poor solderability components will contribute to poor barrel fill, however. This can be identified with a cross-section by seeing solder not wetting to the component lead within the plated through hole barrel.
Technical Support Engineer
Old components may lead to blow holes in wave soldering. As components age the oxide layer on the metal connectors grows. The chemical reaction between the flux and the metal oxide creates gasses. As the oxide level grows, the amount of gas generated increases. These gasses will escape from the solder and the escape route is typically a blow hole.
To be honest not normally as there should be nothing on the components to attract moisture in the first place. More than likely to be the PCB especially if HASL finished or Silver.
Technical Sales Manager
BLT Circuit Services Ltd
In general the older the component gets, the more the oxidation builds up on their leads. In the soldering process (reflow, selective soldering, wave soldering) the flux is applied to clean up this oxidation build up. There is no doubt that the older components are more likely to exhibit blow holes in the solder connections than the new components.
Engineering and Operations Management
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