Hi Dave!

Process development with BGAs, particularly tight pitch ones, is always painful--especially if you can't afford to lose ANY parts.

You don't say whether you are Pb-free or not. The 215C sounds adequate for SnPb, but not standard Pb-free alloys.  Most BGAs are now Pb-free, and attaching them with SnPb can be extremely difficult to get right.  Search TechNet archives for more on that subject.

Measuring the device temperature is a reasonable starting point.  You can also monitor the temperature of the circuit board adjacent to the part.  If both are in a reasonable range for reflow, then you try a part and then use XRAY or cross sectioning to see if the joints collapsed properly and appear to be reliable.  If you can't destroy anything, then you measure the amount of joint collapse due to the reflow process, carefully examine the visually inspectable joints, and XRAY the one's you can't see.  The XRAY exam works much better if you don't use completely round pads to attach to--distorted joints are easy to see and clearly indicate wetting.

Good Luck!

Wayne Thayer 

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of David Tremmel
Sent: Thursday, July 26, 2007 5:22 PM
To: [log in to unmask]
Subject: [TN] microBGA rework

Hello gurus of the Technet,

 

 

We are trying to rework some microBGAs but there is not enough room under the parts for a thermocouple and drilling a hole through the board is not an option at this point.  

 

We are placing a thermocouple on the top of the components being reworked and covering it with Kapton tape and the thermal profile we are using is maxing-out at 215° C.

 

 

Does anyone have experience measuring the component temperature and not the solder temperature and would they mind sharing their results?  Are we asking for field defects because we are not measuring the solder temperature?

 

 

Thank you in advance,

 

David Tremmel

(847) 858-5540 - Cell

 


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