There is always a small amount of voiding seen in "flat" solder joints such as larger chip capacitors/resistors, or under belly pad components, etc.
However, there should not be so much voiding seen that you would ever get a failure at ESS.
There are solder pastes available that display a significant reduction in voids, as well as improved wetting.
If you are uncomfortable with the amount of voiding being seen, you may wish to evaluate a new paste, but be prepared to perform a thorough qualification, including for solder fines, wetting test, slump test, etc.
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Lum Wee Mei
Sent: Wednesday, September 21, 2011 9:08 PM
To: [log in to unmask]
Subject: Re: [TN] large parts falling off finished surface mount board assemblies
Dear All,
Recently, I was tasked to take over the x-ray imaging for the BGAs after the PCB has been assembled. Since I am doing the X-ray and curiosity get better of me, I scan through the rest of the components mounted on the PCB. Hey Presto! I saw solder voids which should not be there at all. What surprise me is that all these solder joints exhibit good fillets and wettability acceptable by the IPC standard for castellation and gull-wing packages. I am surprise to see solder voids as large as the width of the component leads are observed. Some of the solder joints even have multiple solder voids of various degree in diameter per solder joint. There is a 4-pad component that particularly have all 4 pads full of solder voids per pad and some of the voids >25%. As these assembled PCB has yet went through ESS, I am not sure whether I will be seeing any fallen parts, not to say any potential failure when they are delivered to our customer much later.
As it is a norm to have only BGAs x-ray to assess the solder workmanship, have I open up the 'Pandora box'?
Thanks and Regards,
~ Wee Mei ~
________________________________
From: TechNet on behalf of Inge Hernefjord
Sent: Thu 9/22/2011 2:47 AM
To: [log in to unmask]
Subject: Re: [TN] large parts falling off finished surface mount board assemblies
>
>
> I understand that this is of interst for some non-experts, so I add some
> more pictures on DIG this time. You can see the microstructure as a function
> of time in the autocatalytic bath.I have borrowed the photos from Uyemura,
> which we used a lot.
>
> I have much better images done by myself. Will send to Dr Gregory if I
> find them.
>
> So, 4 more images offline to you Carl.
>
> (I'm always wondering why so few people are interested in the surface
> microstructure.)
>
> Inge
>
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