Hi TechNet - Flatness has been the biggest reason for the "unfused" requests for tin or solder finishes per many discussions in the solderability committees. However, there are two very divided, distinct groups: people who have no solderability problems with "unfused" tin/solder finishes and people who have disastrous solderability problems with "unfused" tin/solder finishes. The IPC Steam Aging task group will be publishing its report on various finish reactions with steam aging and solderability testing - the "unfused" solder finishes performed very well. My experience with "unfused" solder finishes has be bad - heavy oxidation of the finish with diffusion down/up the grain boundaries to the copper leaving oxidized intermetallic. This unfused finish was reasonable thick enough that you would not have suspected the diffusion problem. I have published data that states the reason for "fusing" the finishes is to change the solder grain structure to reduce oxidation and prevent diffusion problems. Again there are two camps on the issue. Dave Hillman Rockwell Collins [log in to unmask] ______________________________ Reply Separator _________________________________ Subject: Re[2]: Unfused Solder and/or Tin Author: [log in to unmask] at ccmgw1 Date: 10/17/96 3:15 PM Rudy, Dave, I concur with the flatness issue. Have seen several customers request "no reflow" to achieve flat pads without changing their processes to accommodate for gold or OSP's. I would believe Rudy's comment to be true about requiring a more aggressive flux being needed to activate the surface. I have also had customers request a minimal thickness of plated tin/lead unfused on an MCM-L. They were "pasting" the pads, which were in fact becoming the lead-frame attachments for a QFP, with a higher temp solder (90/10 I think). This is so that the frame would withstand the subsequent solder operations when the MCM-L is mounted on the PWB. Regards, Tom ______________________________ Reply Separator _________________________________ Subject: Re: Unfused Solder and/or Tin Author: [log in to unmask] at INTERNET_GATEWAY Date: 10/17/96 11:18 AM Rudy, I believe the primary reason is that it is Flat. Finish flatness is critical to many SMT component placements and if the assembler can solve the other issues you mention they might have a winner. I do know a company that customer was requesting a very thin unfused tin-lead plate for flatness issues. Regards __________________________________________________ David W. Bergman, V.P. of Technical Programs IPC 2215 Sanders Road Northbrook, IL 60062-6135 847-509-9700 x340 Phone 847-509-9798 Fax email [log in to unmask] www http://www.ipc.org faxback support 800-646-0089 --------------------------------------------------- On Thu, 17 Oct 1996 [log in to unmask] wrote: > Recently had occaision to have some problems associated with recovering > scrapped PCB's that have as final finish UNFUSED plated Tin or Solder (wasn't > sure which). Is there anyone who can enlighten me as to why an > assembler/user would want such a finish. The finish oxidizes heavily, and > quickly, and I suspect likely needs to be cleaned immediately before > soldering, or alternately requires a flux so active that it will etch the > substrate if not washed off in a few minutes.... > > Other than that, it is likely wonderful?? > > Can anyone help me understand this strange (to me) finish? > > Rudy Sedlak > > *************************************************************************** > * 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. * *************************************************************************** *************************************************************************** * 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. * ***************************************************************************