Printed Circuit Board Assembly & PCB Design SMT Electronics Assembly Manufacturing Forum

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


Solder balls on Ceramic

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#63978

Solder balls on Ceramic | 21 March, 2011

I am having issues with Solder balls on Ceramic devices, all LEAD FREE SOLDER. The cermaics are only 7x5mm in size. The balls appear around the 0402 capacitors. I have a varying humidity from 15 to 40 %rh which is slightly low but I cannot control. These devices sit in a pallet through the SMT line, the variation between pallet tollerence, stencil and device tollerence is a factor. Any ideas on preventing sodler balls? Has anyone experience with Ceramic/reflow profile.

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#64025

Solder balls on Ceramic | 25 March, 2011

Are the solder balls what we would call ' mid chip ' solder balls where a single or sometimes a few larger solder balls are positioned somewhere along the side of the chip or are they the solder paste powder particles spread around the pads ?

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#64026

Solder balls on Ceramic | 25 March, 2011

We have the occasional solder fine but the main issue I have is with small - large balls of solder around an 0402 capacitor. Our LF paste data sheet states a %rH of 25 - 70, I have recorded an average for March of 14.9 - 38.5 %rH. Every other requirment is being met (I think!!). Any ideas?

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aci

#64028

Solder balls on Ceramic | 25 March, 2011

Have you checked your reflow profile? You need top make sure that you are with the specification of the solder paste. We currntly use the Kic thermal profiling device.

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#64029

Solder balls on Ceramic | 25 March, 2011

If other solder joints are okay then it is unlikely to be a humidity / moisture in the paste issue...or even too dry paste. Pad size and spacing and aperture size may need checking. Too much paste can cause this issue. Also, check profile ramp rate from room temp to @ 140 C...if it is too steep (> 3 deg / sec) then the flux can slump from the paste and solder is carried with it off the pad and will form balls. Finally, are your pcbs dry ? Pass a bare one through the reflow oven before you print any paste on it, let it cool and then process as normal....if there are no solder balls then the pcbs have too much moisture in them. Sounds strange but I had this issue with a paste customer....excess moisture in pcbs was causing solder balls on chips but no other issues.

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#64037

Solder balls on Ceramic | 28 March, 2011

Graham, good idea about reflowing first. I'll try this out. Our product is Ceramic, not PCB. I'll check the reflow as you say, though I have trialed various shapes and I am in contact with stencil manufacturer regarding aperture sizing. Thanks.

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#64062

Solder balls on Ceramic | 31 March, 2011

I would suggest doing an aperture reduction on your stencil or move to a thiner stencil.Please check that your housekeeping related to stencil cleaning is monitored.

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