Solder material costs increased significantly this year that is increasing overall costs for users. It is understandable that the goal is to seek for lower cost alternatives. Solderpastes with low-melting point leadfree alloys represent a cheaper alternative against “traditional” SAC305 alloy versions.
But what makes them an added value solution from technical point-of-view? In case of a double sided board where for example BGA components are soldered in the first reflow, the second reflow process imposes a serious thermal load on the board so that BGA connections may remelt and due to warpage of the board imperfections may arise at the BGA connections that are difficult to detect. If BGA components are solder in the second reflow HIP (head-in-pillow) or NOW (non-wet-open) type defects will be more probable because of the double significant warpage of the board.
By using low-melting leadfree solderpaste warpage at the second reflow pass will be reduced. If BGA components are soldered in the first reflow in the second, already much lower heat impact, reflow pass the BGA joints will not remelt at all! If BGA’s are soldered on the second side the abuve mentioned defects will have much lower probability due to lower thermal excursion. BGA balls in this case will not melt at all, they are rather soldered as solid terminals.
Development of low-melting leadfree solderpastes advanced a lot in recent years. Today we can state that such product exists that unifies the above benefits and leads to the combination of cheaper material and cheaper process (less energy cost, probable use of pin-in-paste technology to replace wave soldering step and opening the way for using less heat resistant and thus cheaper connectors) one can manufacture more reliable products.
If you find this option interesting for further discussion or for testing in your environment please contact your Deery Brook representative.