Hi Steve - No, you are not oversimplifying the problem. It's just that getting the "rework" portion of the recipe right is not very simple. A fair share of the industry looks at solderability problems as having two main source causes: oxidation and intermetallic growth. Chris Hunt at NPL has some really good info on intermetallic growth and growth prediction equations - check out the 96 SMI proceedings for his paper. The area I see lots of misconceptions is how to restore an oxidized solder finish. If you had a thick solder finish that is just plain oxidized without any copper/tin intermetallic complications then a controlled process reflow with the right flux chemistry will make things solderable again. If you have a thin solder finish that has converted (via diffusion) itself into a copper/tin intermetallic you need to use a very aggressive flux to attack the intermetallic oxide and then build up/deposit a reasonable thickness of solder (say 60-120 microinches). If you just re-process the thin solder scenario without increasing the solder thickness the copper/tin intermetallic just reforms and oxidizes again -now you are back at square one. If I would quickly (within a few days) process these thin solder scenario boards in my assembly line with the right flux chemistry I would have adequate yields - solderability goes down hill if the boards sit around. That's why you will hear some camps say a reflow will restore an oxidized board (the JIT type of processes) or hear some camps say a reflow won't restore a board (the long storage time processes). There are some new restoration/fluxless solder technologies that are in the work too (e.g. ROSA, PADS etc.) that may help everyone in the future if they prove viable. Dave Hillman Rockwell Collins [log in to unmask] ______________________________ Reply Separator _________________________________ Subject: Re: "Tinning house" Author: [log in to unmask] at ccmgw1 Date: 1/23/97 11:35 PM Dave, I have been following your discussion on solderability (root causes of excessive oxidation) and am lead to believe that if porous/thin tin leads are "reworked" properly by these tinning houses we could avoid the many inventory problems (storage time, slow moving parts, bagging with desicant, etc.) and still maintain or improve solder connection reliability. The eventual/ultimate solution being to get the OEM's with poor tinning corrected or off the approved supplier list. Am I over simplifying with this conclusion? Steve Ross *************************************************************************** * 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. * *************************************************************************** * If you are having a problem with the IPC TechNet forum please contact * * Dmitriy Sklyar at 847-509-9700 ext. 311 or email at [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. * *************************************************************************** * If you are having a problem with the IPC TechNet forum please contact * * Dmitriy Sklyar at 847-509-9700 ext. 311 or email at [log in to unmask] * ***************************************************************************