Jim,
     
     I appreciate your response, however the issue does not entirely relate 
     to solderability. The main reason for tinning these components is due 
     to lead (Pb) contamination. The production solder contains Indium 
     which when contaminated with as little as 5% Pb will reduce the 
     melting point to as low as 178 degC. The operating range for the 
     product is from +175 to 200 degC.
     
     In summary, what we are really trying to do is minimize the Pb 
     contamination from the component lead.
     
     Thanks,
     
     Darrell
     DRAKE@SSDRDCC
     (713) 987-4365


______________________________ Reply Separator _________________________________
Subject: RE: Component Lead Tinning
Author:  [log in to unmask] at Internet-Mail
Date:    10/6/95 4:28 PM


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Darrell Wrote:
     
>     I am looking for some technical information/ assistance regarding 
>    component lead tinning. 
>
>  Does anyone have any experience with a tinning process causing thermal 
>    shock to integrated circuits that would cause them to separate at the 
>    lead frame bond ? What is an acceptable thermal ramp rate ? 
>    
>    The solder pot is held at 313 deg. Celsius (high temp solder), the 
>    component is suspended in type "RMA" flux for 5 seconds and then 
>    suspended in the solder pot for another 5 seconds. This process is 
>    repeated for two cycles. We are using an automated tinning machine 
>    which controls emmersion speed and depth for both the solder and flux. 
>    
>    What is the typical thermal ramp rate that a component, such a DIP, is 
>    able to withstand ? This includes the cool-down (second immersion into 
>    flux prior to second tinning cycle is approximately 8 seconds).
>   
     
If tinning at a high temperature is a problem, why not tin using eutectic 
(lower temp) solder which will result in a solderable surface at a lower 
temperature?
     
Jim Marsico
AIL Systems