In a message dated 4/13/99 12:27:46 AM Pacific Daylight Time, [log in to unmask] writes: << Can someone help with the processing of a heavily populated SM PCB, SM top and bottom which has to be reflowed both sides and has through holes parts ( no wave solder ). Any guidelines on how this should be processed would be of great help ie what side is the high temp solder used on, most densly least densly populated etc etc. Regards, ken Robertson Telspec >> Hi Ken! I'm assuming that the reason you must do double sided reflow is because the board either has fine pitch or BGA's on both sides, am I correct? As far as using different melting point solders, I know there's some info out there that discusses that, but I really don't think that's a good thing to do. Just say for instance; what if somebody screws up and prints the wrong paste on the wrong side? You really don't need to do that anyway. Just about any component I can think of (as long as IPC guidlelines have been followed as far as pad layout and footprint) has enough surface tension to stay put when solder goes liquidous on the bottom...(provided your board isn't bowing and the reflow oven conveyer is smooth running). The exceptions to that are extremely heavy parts like ceramic or metal bodied QFP's and PLCC's, or parts with attached heatsinks. Sometimes Melfs will give you problems, or I've had problems with 4-leaded plastic body oscillators and certain filters too. Basically, suspect the parts that don't have much lead area to 'em. The figure I remember, and many people say this is pretty conservative, is that you'll have 30-grams of surface tension for every square inch of lead surface. As far as what side to do first, I usually leave the side that has the finest pitch on it for the last side. If ya got any other specific questions, let us know... -Steve Greory- ################################################################ 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's web site (http://www.ipc.org) "On-Line Services" section for additional information. For technical support contact Hugo Scaramuzza at [log in to unmask] or 847-509-9700 ext.312 ################################################################