In message <[log in to unmask]> [log in to unmask] writes: > I would like your opinions and experiences using low-melt solder alloys for > rework of smd. The mixture contains tin, lead, and bismuth. What > potential problems are associated with this combination? It's an interesting concept, one which we have been considering. The process involves reflowing a LMP (low melting point) solder into the existing solder joints, using a soldering iron or hot air pencil (and optionally using some under board heating). The LMP solder mixes with the existing stuff to form a mixture which stays molten at a much lower temperature than standard 63/37, and therefore stays molten much longer, even when you remove the heat source; so, you can take off even a large QFP device having just used a soldering iron or hot air pencil. I see pros: 1) Very inexpensive on the equipment side, no capital investment needed 2) Can be done anywhere (in the field) I see cons: 1) Material (which is a tin/lead/bismuth/indium type combination) is expensive, so not really a process for people doing lots of rework 2) It is vital that the LMP solder and mixtures be removed from the pads before a new component is placed and soldered, otherwise your joint could reflow at a low (maybe operating!) temperature 3) Won't work for BGAs and other array devices Para 2 is what worries me; no matter how well you wick off the LMP solder from the pads, I think you will still have a (thin) layer of bismuth- bearing intermetallic left on the pad. When a new joint is made with conventional solder, the bismuth will stay at that interface (not being very mobile). Bismuth being brittle, I reckon the new joint is much more likely to fatigue crack at the joint/pad interface. So, reliability suspect? I dunno, no data, just theory. Maybe the approach is valid for the hobbyist or the occasional job in a low-tech consumer product (Class 1). Other inputs appreciated. Some info from a company who have commercialised this process can be found at http://chipquikinc.com (I offer this for your interest, not as an advertisement - sheesh, some people are sensitive!). Peter -- ::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::: Peter Swanson Oxfordshire, England INTERTRONICS [log in to unmask] http://www.cygnetuk.demon.co.uk Suppliers of materials and consumables to the electronics & related industries ::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::: ################################################################ 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 technical support contact Hugo Scaramuzza at [log in to unmask] or 847-509-9700 ext.312 ################################################################