Reflow soldering boards with components on both sides?

FlyingFishFinger

Seems to me with my limited knowledge of soldering techniques that this isn't possible. We are designing a small PCB about the size of a Stamp that has SMD components on both sides, and the number of boards we are going to need ultimately will run around 30. There are one or two skilled hand-solderers on our team, but assembling 30 small boards with components down to 0603 size might be rather too time consuming and error-prone.
What sort of alternatives are there to (expensive) commercial assembly services? We are deciding between purchasing a module that will ALMOST handle our requirements for ~$30 each and adding some extras onto the carrier boards or making our own module, so any assembly cost should hopefully come close to the same price, in volume.
Any suggestions?

Rafael

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mctrivia

you can reflow both sides of a pcb. as long as the right temp curve is used(most important not at high temp to long) the components on the bottom will not fall off. Personally I reflow one side then hand solder the other. If you keep one side free of the difficult parts this method works well.

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WBA Consulting

Double-sided reflow works because the surface tension of a joint without flux (IE: the first side after initial reflow) is strong enough to hold the part onto the board while the parts are upside down during the secondary reflow pass. Typically, the bottom side of a board is ran first and is usually designed with low mass parts (caps, resistors, small ICs, etc). The higher mass parts are placed on top and ran through the secondary reflow. If a large part has a high amount of surface tension (IE: many leads or an underside thermal pad) they can be processed on the initial side of a board without them falling off during the secondary reflow pass.

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