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

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.

capacitor charging



capacitor charging | 4 April, 2004

I'm involved in backplane manufacturing process. There are about 10 electrolitic capacitor assembled in my board.These capacitor are soldered using a selective soldering machine. My problem is that these capacitor will charged up and failed as short at ICT. Currently we have to connect a wire between the capacitor leads to discharge the charge, and once this was done and retested at ICT it will pass. This problem started since we are using the selective soldering machine cause earlier we are hand soldering these component in which we didnt see this problem. I have checked the grounding on the selective soldering machine body and its all ok. My question are how can the capacitor charged up in the soldering machine? Is it due to electromagnet interaction in the machine or something to do with electrostatic? Did anyone know any websites offering these information?

Pls help me! cyclopsn

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capacitor charging | 5 April, 2004

While a temperature, check the AC voltage to ground on the tip of your selective soldering machine.

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Tom B.


capacitor charging | 11 April, 2004

You should add a Capacitor Discharge statement in ICT test Software. This could be done by selecting the nodes and have statements to connect relays to ground.

Could be possible that the Selective Soldering system is the cause, as problems is now showing up. Has any other changes been incorporated besided selective soldering? Are both leads soldered at same time? or individual? Have you tried measuring the voltage of the caps before discharge? Also what are value of Caps? I know high value caps such as 10,000uf to 1F can charge statically.

Have you checked for voltage of nozzle to ground. Possible ac induction from heaters? Are they inductive or resistive?

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