Hi, FYI Alvin Engelmaier wrote: > > 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. ################################################################ 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 ################################################################