Steve,
     
     Component solderability can be a difficult problem to solve. You are 
     correct in expecting your component suppliers to provide solderable 
     leads. Dave Hillman's response details some of the things that can 
     happen to the component/lead finish to degrade solderabiity. There are 
     others as well. To your point on rework, a hot solder dipping house 
     should be able to restore the solderability of your components. A 
     quick check to estimate the kind of rework required would be a simple 
     dip and look of a component from a questionable lot using r flux and 
     245 c solder for 5 seconds. If the component solders well, a reflow or 
     redip operation may well suffice. If the component exhibits edge dewet 
     around the perifery of the leads, or in larger "patches" then an 
     oxidized intermetallic or basis metal problem or plating process 
     problem may exist and a strip/resolder dip rework may be indicated.
     If your "quick check" reveals gross dewet or nonwet, and the "tinning
     house" ( actually it should be called solder diping house ) tells you
     a quick redip will fix it, I would be skeptical. It would be bad if 
     you expected a quick turn around on your parts and find that when you 
     get them back, they were only marginally improved and still resulted 
     in solder defects at the board level.
     
     Best regards,
     
      Mark Kwoka
      Harris Semiconductor


______________________________ Reply Separator _________________________________
Subject: Re: "Tinning house"
Author:  [log in to unmask] at smtp
Date:    1/23/97 10:11 PM


Dave,
I have been following your discussion on solderability (root causes of 
excessive oxidation) and am lead to believe that if porous/thin tin leads are 
"reworked" properly by these tinning houses we could avoid the many inventory 
problems (storage time, slow moving parts, bagging with desicant, etc.) and 
still maintain or improve solder connection reliability.
The eventual/ultimate solution being to get the OEM's with poor tinning 
corrected or off the approved supplier list.
Am I over simplifying with this conclusion? 
Steve Ross
     
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