TECHNET Archives

1996

TechNet@IPC.ORG

Options: Use Monospaced Font
Show Text Part by Default
Show All Mail Headers

Message: [<< First] [< Prev] [Next >] [Last >>]
Topic: [<< First] [< Prev] [Next >] [Last >>]
Author: [<< First] [< Prev] [Next >] [Last >>]

Print Reply
Subject:
From:
"ddhillma" <[log in to unmask]>
Date:
Wed, 16 Oct 96 13:08:26 cst
Content-Type:
text/plain
Parts/Attachments:
text/plain (123 lines)
     Hi Richard - in response: 
     
     1.  If a leadframe is made from Alloy 42, is there ALWAYS a concern 
     that the part will stress-crack after thermal cycling, especially on 
     stiffer leaded devices?
     
     * If you read through some of the recent publications on alloy 42 
     leads you will find that no, an alloy 42 lead frame does not 
     automatically result in solder joint cracks. The lead material is just 
     one variable in how a solder joint survives each use environment. But 
     because alloy 42 leads are less compliant (than say copper leads) it 
     does mean that you are trading off some reliability. Take a look at 
     Engelmeir's, or Lau's or Iannuzzelli's publications.
     
     
     2.  Does the exact sequence of plating have any effect on the 
     survivability of the device after cycling?  For example, do Alloy 
     parts that are overplated with nickel or silver, then tin-lead survive 
     better than Alloy 42 frames with only tin-lead?
     
     * I believe that the plating sequence doesn't matter provided its good 
     to begin with. But, I don't have any data to support that and I think 
     most of the published papers are dealing with solder or solder/nickel 
     over alloy 42.
     
     
     
     3.  Is there general agreement that this problem reared it's head 
     because of the attempt to use commercial parts for military or harsh 
     environments?  This would imply that engineering is choosing the wrong 
     parts for the application, and that the original part manufacturer is 
     making 'good' commercial parts. (And further, that an 'acceptable' mil 
     part no longer exists!)
     
     * A general agreement by industry? That would be neat! Seriously, this 
     problem is the result of misapplication of a material in a design 
     where it is not optimum. Both the designer and assembler need to do 
     their homework (hopefully as a team) to avoid having problems like 
     this.
     
     
     
     4. If the root of the cracking problem results from the manufacturer 
     allowing the Alloy 42 to tarnish before tin plating, is there anything 
     that can be done except for the horrific task of trying to 
     solderability test an SMT part? 
     
     * Solderability testing is the only way I know of for catching the 
     problem. Working closely with your component vendors would be one 
     method of avoiding a plating problem too.
     
     
     Dave Hillman
     Rockwell Collins
     [log in to unmask]
     


______________________________ Reply Separator _________________________________
Subject: ASSY:  Alloy 42 Plating Questions
Author:  [log in to unmask] at ccmgw1
Date:    10/14/96 12:09 PM


There has been a recent flurry of discussion on Alloy 42.  
We've also seen some post-thermal failures in which Alloy 
42 MIGHT be implicated. I have some specific questions I 
hope someone can clarify. I've just rejointed TechNet and I 
haven't been able to find the last months' discussion in 
the archives. :-)) 
     
1.  If a leadframe is made from Alloy 42, is there ALWAYS a 
concern that the part will stress-crack after thermal 
cycling, especially on stiffer leaded devices?
     
2.  Does the exact sequence of plating have any effect on 
the survivability of the device after cycling?  For 
example, do Alloy parts that are overplated with nickel or 
silver, then tin-lead survive better than Alloy 42 frames 
with only tin-lead?
     
3.  Is there general agreement that this problem reared 
it's head because of the attempt to use commercial parts 
for military or harsh environments?  This would imply that 
engineering is choosing the wrong parts for the 
application, and that the original part manufacturer is 
making 'good' commercial parts. (And further, that an 
'acceptible' mil part no longer exists!)
     
4. If the root of the cracking problem results from the 
manufacturer allowing the Alloy 42 to tarnish before tin 
plating, is there anything that can be done except for the 
horrific task of trying to solderability test an SMT part? 
     
Thanks,
     
----------------------
Richard Huziak
Manufacturing Engineering
SED Systems
Saskatoon, SK, Canada
[log in to unmask]
     
     
*************************************************************************** 
* TechNet mail list is provided as a service by IPC using SmartList v3.05 * 
*************************************************************************** 
* To unsubscribe from this list at any time, send a message to:           * 
* [log in to unmask] with <subject: unsubscribe> and no text.        * 
***************************************************************************
     



***************************************************************************
* TechNet mail list is provided as a service by IPC using SmartList v3.05 *
***************************************************************************
* To unsubscribe from this list at any time, send a message to:           *
* [log in to unmask] with <subject: unsubscribe> and no text.        *
***************************************************************************



ATOM RSS1 RSS2