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Voids in the joints

Vincenzo Longobardo

#16980

Voids in the joints | 20 December, 1997

what is your experience about the presence of the voids in the joints ? Are they dangerous and when ?

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Justin Medernach

#16983

Re: Voids in the joints | 22 December, 1997

| what is your experience about the presence of the voids in the joints ? | Are they dangerous and when ? Vincenzo, Voids in solder joints can be caused by a number of factors. Let's begin with the flux vehicle in your soldering media. If the proper coverage of flux does not occur, it is very possible that you may have voiding issues. Voids may also be caused by "blind" vias within the pads which have moisture entrapment and the outgassing of the moisture causes a void. It can simply be a matter of a poor thermal profile. Another factor which may affect the integrity of the solder joint is the solderability of the items to be soldered. If the land pad's surface finish is partially oxidized and the flux vehicle is incapable of cleaning the oxidation, voids will definitely occur. Likewise, if the metalized surfaces of the components are oxidized, you will have poor solderability and potential voids. This can easily be inspected for using a solderability tester. Check the used equipment market, they are prevelant and cheap. As far as the danger of voids, there are a few but they are critical. If the application is in a thermal stress environment. The structural integrity of the joint will be compromised by the void and you may have catestrophic failure. Another potentially serious problem caused by voids is flux entrapment. If the void has access to the ambient environment, we shall call it a hole, flux will have access to the underside of the component. This flux entrapment will eventually eat away at the component and the substrate and will more than likely cause an electrolytic failure. I'm not sure if the electrical functionality of the component is compromised by voids. I would say that mechanical failure is probably the most prevelant problem caused by voids in a solder filet. I hope I was of some help. Best Regards, Justin Medernach Flextronics International

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Earl Moon

#16982

Re: Voids in the joints | 19 February, 1998

| what is your experience about the presence of the voids in the joints ? | Are they dangerous and when ? My specifications require rejection and study if voiding exceeds 2% of solder joint volume measured using x-ray and/or x-sectional analysis. My studies show, for BGA's, chip devices, and some leaded device types that solder joint failure is immenent when this % reached. Causes are simply determined using SEM/EDX, as an example, and usually are associated with contamination as excessive tin oxides, as an example, and are preventable the next time at the design level by carefully specifying component and pcb metallization requirements, as an example.

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Earl Moon

#16981

Re: Voids in the joints | 19 February, 1998

| what is your experience about the presence of the voids in the joints ? | Are they dangerous and when ? Correct from 2% to 20% voiding unacceptable.

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