- Mon May 28, 2007 8:24 pm #30626
the float, in conjunction with a solder mask makes for automatic alignment of parts. especially for ICs. This is an issue for home made boards with out a solder mask.
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Philba wrote:the float, in conjunction with a solder mask makes for automatic alignment of parts. especially for ICs. This is an issue for home made boards with out a solder mask.Greetings Philba,
propellanttech wrote: This is usually from them smt pad being larger than the component soldering location. The surface tension of the molten solder will pull harder on one end than the other......resulting in a tombstoned part. This usually happens from more solder than required to attach the component to the board. A smaller pad would require less solder....and the surface (smaller quantity) tension of the molted solder doesn't lift the part.Greetings James,
propellanttech wrote: You should know that when hot air soldering.....turn the air volume down as low as you can get away with. The air flow will provide an addition lifting sorce for the parts. This could result in some very frustrating moments. I have done some rework to my boards.....and have found out the hard way.My equipment is primative - a Weller 6966C heat gun that I bought (used) for applying heat shrink. I recently discovered it can melt solder, and use it by hand in small circles around three or four 1206 parts to do the conversion of paste solder. So far I've only used 1206 size, some other parts as noted earlier, and some SOIC28 or TQFP32 devices.
propellanttech wrote: I'm also very careful about placement.....make sure your parts are pushed down into the solder.......don't go crazy....but make sure they are in contact with all their landings. This helps prevent one side lifting. (But this is theoretical....and my opinion)I'm dotting all the pads with paste on one side of the PCB, then placing the parts with tweezers. I try to get them all lined up and seated on the pads. I was tacking pin 1 of the ICs but now I feel this is not needed (the entire IC can pull to the pad centres if solder on all pads is molten).
propellanttech wrote:...If by heat gun you mean the cheapo $30 ones, I totally agree. They seem to have 2 settings - nuke and thermo-nuke. However, a hot air station with regulated and controllable heat and flow works really well. The only thing tricky for me was learning to do a pre-heat pass. Once I figured that out, it was really easy and fast. I'm happy with my hot air station.
I will warn you about the heat gun method. Becareful....heating just part of the board can cause it to bow or warp. This is not ususally a problem....but can be for some projects.