We have a Corfin tinning cell with a nitrogen blanketed solder pot.  
At the present time we tin down to .5mm pitch with never any bridging 
unless the leads are actually touching.  No pot skimming is required.  
All tinning is accomplished without the use of flux.  It's a snap.

Dave Letendre


______________________________ Reply Separator _________________________________
Subject: ASSY : pretinning of fine-pitch devices
Author:  "D. Terstegge" <[log in to unmask]> at INTERNET
Date:    1/14/97 9:05 PM


In the near future I have to start with pretinning of molded ring 
carriers with a 0.5 mm leadpitch (CQFP256 and a 64 pin Dual Flatpack) ? 
For 0.65 mm pitch devices we do it without any solder bridging, but I'm 
afraid that the 0.5 mm pitch makes it a bit more critical. 

We use a simple tinpot with a component holder and a lever to enable 
steady vertical speed and a controlled dipping depth. Dross is skimmed 
off manually after each component. Flux is RMA.

Since production volumes are relatively small we cannot afford to lose 
many of these (expensive) components for process development. There is 
very limited time between receiving the components and starting with 
board-assembly, and I don't think I have dummies available by the time 
the production starts. All this means that the pretinning just has to 
work, without much process adjustments or equipment changes.
Should I be worried about this ?  Does anyone have experience with 
pretinning of 0.5 mm pitch devices ? 
All comments and technical advices are wellcome. 

--- Daan Terstegge ---

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