Cara OH!!! but yes! With any flux/paste, there is an optimum preheat profile (time and temperature) to obtain a max SIR (of course, different for each flux/paste). This is something that the lead-free enthusiasts have not yet cottoned on to, that the flux formulation must be tweaked for optimum results and that the SIR will drop, partially because the preheat profile will need modifying for optimum results, and partially because of the higher liquidus. This will certainly apply to "no-clean" and also probably to cleaned assemblies, because, by the same token, the residues will be that much more difficult to remove. One of the major factors is the time that the assembly is above the substrate Tg. The Tg itself is not a sharply defined parameter, even if laminate manufacturers quote it as such. It depends on a number of factors, such as the MW of the resin which varies typically in a 3:1 ratio, the absorbed humidity, etc. This means that if the quoted Tg is, say, 130 deg C, and the humidity is high, the real Tg may be over a range of, say 90 - 130 deg C, with a random distribution over the surface. (Dry, it may be 110 - 150 deg C.) Above the Tg, there is more likelihood of ad/absorption of flux components, especially oxygenated long-chain molecules such as some carboxylic acids (activators) and alcohols (vehicles, such as polyglycols). This is one reason why amino-acid hydrohalide fluxes in a rosin matrix, correctly used, often exhibit superior SIR values, because the rosin molecules, being tricyclic, are simply too big to enter too significantly into the resin matrix, even above the Tg. In practice, changes of say +/- 10 deg C or +/- a few seconds will probably have little effect, but it may be that, beyond these limits, the drop will start to accelerate. Brian "Cara.Startek" wrote: > Does pre-heat temperature influence SIR test results? > > Cara Startek > > Process Engineering > http://www.leitch.com > > ############################################################## > TechNet Mail List 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://www.ipc.org/html/forum.htm) for additional > information. > If you need assistance - contact Keach Sasamori at [log in to unmask] or > 847-509-9700 ext.5315 > ############################################################## ############################################################## TechNet Mail List 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://www.ipc.org/html/forum.htm) for additional information. If you need assistance - contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315 ##############################################################