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smt components vs. wave solder



smt components vs. wave solder | 8 November, 2002

Nowadays I have a problem, I am in chsrge of the section of smt in my company, have a normal process inside my department with a minimal level of mistakes, the problem happens when the material is liberated to the lines of production on happened for the wave-solder after this they appear moved components, missing components and missaligment, certainly that previously were not, and checking the whole process I realized that in the wave soder was reach to re-flow (again) the components, the solder paste back liquidates again, according to my experience this not must to pass, it is a very big problem wanted if someone to had a problem since I could you can give me an advice

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smt components vs. wave solder | 9 November, 2002

if you wave solder you have to glue the SMD parts on the bottom side. If you reflow the bottom side then you usually shouln't go over the wave afterwards. It's quite logical the joints melt again, that's what you want to achieve going over the wave.

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Mark J


smt components vs. wave solder | 9 November, 2002

If I understand what you're saying, you are reaching reflow temp's on the top side while soldering bottom side components. You might want to run a glass gauge plate over the wave and make sure your contact pattern isn't too large. If your PCB is in contact with the wave for too long it will tranfer excessive heat to the topside and remelt previously reflowed joints.

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smt components vs. wave solder | 11 November, 2002

Like Mark, I'm guessing your problem is with SMT parts on the top side, the solder is re-melting and some of the parts are moving around during when the board is being wave soldered.

When I had some training on thru hole wave soldering way back when, the target was 3 seconds of contact with solder when you wave solder. If the component leads have more than 3 seconds of contact, the top side of the board might get hot enough to reflow the solder joints on SMT parts on top. The glass plate I use is a special tempered glass with grid lines on it. It is called a Lev Check, made by Hexacon.

When the glass is over the wave solder you can get an idea of how big the contact area is, and how even it is. Handle the glass very carefully while it is hot. Adjust your conveyor speed to get 3 seconds of solder contact. If you are still having a problem you will need to check the preheat temperatures, you may be getting the boards too hot before they get to the wave solder.

Good luck, Mike F

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