Good Morning Werner, Very good input on the solder thickness dilemma. I agree that I have yet to see any real "objective" criteria on solder thickness. I believe that IPC has or is putting together a spec for this situation. The old standard of .0003" (back in the ages of tin/lead fusing/reflow) was a before fusing requirement and after fusing, the standard was "to meet the solderability of IPC-S-804". In our industry, we have come to a "generic" number of 50 millionths minimum at the knee to aid inhibition of the "copper migration issue". On SMT pads, we have seen specs not only for minimum thickness of 50 millionths, but also for planarity callouts within a smt component area. Measurement has been performed with XRF (X-Ray Fluorescent) equipment and statistical data gathered from that. I believe that solder is becoming less of a viable solution for assembly and other alternatives (OSPs', Tin/nickel, palladium, electroless Ni/Immersion AU, etc.) are on the forefront of replacing tin/lead (solder) compounds. I personally like the OSP process due to the ability to easily rework in the event of shelf life situations. That is my 2 cents worth (in today's age of inflation, it's worth less) and hope that others will make this worth a dollar. JOHN WAITE -----Original Message----- From: Engelmaier <[log in to unmask]> To: [log in to unmask] <[log in to unmask]> Date: Thursday, April 09, 1998 11:41 PM Subject: Re: [TN] [TN IPC Test methodes Hi Mike, There is no test method for HASL solder thickness nor is there a general specification for a minimum thickness—and perhaps there should not be. The minimum solder thickness that will assure solderability will depend on the time between the HASL-process and the reflowing of the assembled PCB, because thin solder coatings have a limited shelf life which is also temperature- dependent. This comes from the fact that the intermetallic compound (IMC) layer Cu6Sn5 will grow and thus consume the available tin. This diffusion process is temperature-dependent. As the tin is consumed, the layer above the IMC layer becomes increasingly lead-rich and therefore there will be an increase in the Liquidus temperature making subsequent reflow soldering more difficult if not much original near-eutectic solder remains above it. In the worst case, the IMC can grow to the surface—upon exposure to oxygen the formerly solderable IMC becomes non-solderable. So, you have to judge for yourself, what minimum solder thickness is appropriate for your needs. Anything less than 2 micrometers has a rather limited shelf life, while above 5 micrometers a long shelf life for most reasonable storage conditions is assured. Werner Engelmaier Engelmaier Associates, L.C. Electronic Packaging, Interconnection and Reliability Consulting 7 Jasmine Run Ormond Beach, FL 32174 USA Phone: 904-437-8747, Fax: 904-437-8737 E-mail: [log in to unmask] ################################################################ TechNet E-Mail Forum provided as a free service by IPC using LISTSERV 1.8c ################################################################ To subscribe/unsubscribe, send a message to [log in to unmask] with following text in the body: To subscribe: SUBSCRIBE TechNet <your full name> To unsubscribe: SIGNOFF TechNet ################################################################ Please visit IPC web site (http://jefry.ipc.org/forum.htm) for additional information. For the technical support contact Dmitriy Sklyar at [log in to unmask] or 847-509-9700 ext.311 ################################################################ ################################################################ TechNet E-Mail Forum provided as a free service by IPC using LISTSERV 1.8c ################################################################ To subscribe/unsubscribe, send a message to [log in to unmask] with following text in the body: To subscribe: SUBSCRIBE TechNet <your full name> To unsubscribe: SIGNOFF TechNet ################################################################ Please visit IPC web site (http://jefry.ipc.org/forum.htm) for additional information. For the technical support contact Dmitriy Sklyar at [log in to unmask] or 847-509-9700 ext.311 ################################################################