![]() A reflow temperature of around 225 degree C with an extended TAL (around 60-90 seconds) would be helpful in melting the bumps and also providing sufficient time for the lead to mix within the bulk and the solder to wet. The reflow temperature and time above liquidus are very critical, because of the BGA with SAC bump. C per second.Ī soak time of around 60 -120 seconds for effective dry out of the solvents and good flux activation to minimize voiding. Ī Preheat temperature of around a 120 deg. Since the paste is 63/37 eutectic solder paste I would recommend the following. Karl holds numerous patents, including four for lead-free solder alloys, and was a key developer of no-clean technology. Seelig has authored over 30 published articles on topics including lead-free assembly, no-clean technology, and process optimization. In his 32 years of industry experience, Mr. Depending on your end customer you may need to provide reliability data. Profile the PCB (with all the components populated) to be sure the BGA solder joints achieve the desired temperature, then cross section the solder joints to make sure the solder joint looks homogenous. There are a few vendors today who offer "transition" solder pastes, that are Sn/Pb alloy based, with a flux medium that can survive higher temperatures. Therefore you need to insure that you Sn/Pb flux system is capable of withstanding the higher temperatures without suffering flux exhaustion. Of course it is going to be higher than a standard tin-lead reflow temperature. This paper also provides the methods to calculate the reflow temperature needed in order to get complete mixing (based on the bump size, alloy, and paste deposit). (IPC/JEDEC, San Jose, 2005) summarized some of the previous work, including reliability studies done by Solectron where they showed an impact in reliability, but in some cases may be acceptable, as long as the correct temperature is achieved in order to get complete mixing. (CMAP, Toronto, 2005) showed the disastrous consequences of not completely reflowing the solder joint and having a Pb-rich region in the solder joint. This typically occurs when a "standard" Sn/Pb reflow process is used, the incomplete mixing will have a significant impact on reliability Hillman, et al. When these are used in a Sn/Pb process there can be a significant impact on reliability.Ī worst case scenario is where the SAC bump is not reflowed or only partially reflowed. This in turn causes the package manufactures to produce predominately Pb-free bumped packages. ![]() Manufacturing with a mixed metal system is, unfortunately, becoming more common as high volume manufacturers move to Pb-free. ![]() Using a water soluble 63Sn/37Pb paste, what are the optimum profile settings to assure no voids or "IPC acceptable" voids?įor settings I'm looking for times and temperatures for both the soak and above liquidus zones. We have an ENIG plated PCB that is entirely leaded except for one BGA which has SAC305 for balls. ![]()
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