The key word here is "IF" (the operators..etc.). A rework or a repair should be designed, like any other process, to accomplish the intended function without degrading the design reliability of the item. - You need to look first at the maximum rate of temperature change which chip components can tolerate without damage (most component manufacturers provide that information). Capacitors are especially sensitive to high rates of change and should be preheated prior to installation, rework or repair. - It seems that most rework/repair actions are conducted in something less than a "planned" manner and frequently operators are encouraged to "get these 20 assemblies finished before lunch". In those conditions the "IF" seems to be put on the shelf until the rush is over. You can make a strong argument that the rework and repair operations need to be a more closely controlled process than the initial manufacturing process because of the higher number of variables involved. Preheating both the assembly and the component are considered essential process steps here at the EMPF, and are reflected as such in the repair classes we teach. Failure to preheat engenders the risk of two distinct liabilities: 1) damage to (either or both) the component and printed wiring board during the procedure and, 2) latent damage (micro fracture) of the component (not detectable during post-rework/repair visual inspection) which will negatively impact reliability. - You need to be guided by your customer's quality needs. The Class of equipment you build (IPC ANSI/J-STD-001 definition) is a pretty good indicator of how you should design the rework/repair processes. - No, as far as I know we do not have a paper or study documenting the need for preheating. Regards, Jim Moffitt/EMPF At 09:48 AM 10/10/96, you wrote: >Dear Technet, > >We are a military assembly house that employs preheating >plates for ceramic chip rework to reduce the risk of >internal chip delamination from thermal shock. >This has been done per IPC recommendations. However, this step in the >rework process is time consuming and cumbersome. We have done >minor and informal tests to determine the real value of this >practice and found that it really is not needed if the operators take >care in their soldering. If the tip size and heating time is >controlled, there doesn't seem to be an immediate effect or a >temperature cycling effect on the chips. > >I am interested to see how widespread the use of preheating >plates actually is. I would like to hear from anyone having >any experience indicating that the process is actually necessary. >(or not necessary) > >Thank you in advance for any input. > >Jason Spera >Manufacturing Engineering >General Atronics Corporation > >*************************************************************************** >* 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. * ***************************************************************************