We have a current problem on our packages after we bake it for 24 hrs prior BGA rework. Flux or white residues found on the connector leads and terminals that cause not contact problems during mating. Could you help us how to clean the fluxes properly and how could this phenomeon happenned?
As we understand it, you: * Get some nice BGA from your supplier * Find BGA to be packaged properly * Bake the BGA for 24 hours at [what temperature?] to reduce the potntial for damaging moisture sensitive components during following processes * Remove BGA from oven and prepare to rework a board * Observe the BGA making poor contact with the board, because the BGA connector balls are coated with a white residue
What changes would you make with this interpretation of the concern that you have?
thanks for your reply, actually we bake the PCB assembly prior the rework because the package was exposed for quite some time already. The baking time was 24hrs @ 125 deg.C. We notice that there were flux residues on the connectors after the baking.
We just neglect it and we proceed to BGA rework, after repair of the BGA, we process through the assembly, then it was detected at testing process that it has connection problems on the connector.
First, we assume the white residue is only on the connector and not on other components. That would imply that either: * White stuff was on the connector when it came in-house from your supplier. [Confirm this theory by baking some connectors from stock.] ... OR * White stuff is a reaction between the stuff on the connector when it came from the supplier and the stuff you put on it during assembly. [Perform experiment to confirm this theory.]
Second, the results of your testing suggests that either the connector was: * Never soldered well ... OR * Came unsoldered during rework of the nearby BGA
... which is it?
Next, the method for cleaning the white residue on the connector will depend on the composition of that material. You say that it is flux. What type of flux do you have on the connector?
Finally, whenever we hear "white residue" and "flux" used in the same sentance, we think: "low residue flux and water". Together low residue flux and water cause the flux residue to go milky white. [Hint: IPA is 50% water.]