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. * ***************************************************************************