Wave Soldering - Fixtures

Fixtures

The printed circuit board with through-hole components on top of the board and/or surface mount components glued on the bottom side are sometimes placed on a fixture. The fixture is a fiberglass composite or titanium frame with openings exposing the components to be soldered. Wave solder fixtures are required for PCBs where bottom side components cannot be exposed to the solder, or the board is either too small or has a non rectangular shape and cannot be 'picked up' by the titanium fingers. The fixtures can also be used to incorporate clamping and alignment devices designed to hold components in place and prevent 'lifting' of the components as the leads hit the wave, whilst ensuring correct vertical alignment. In some cases fixtures are also used to reduce changeover time by having fixtures of the same width for different assemblies. This way no changes are needed for the conveyor of the wave solder. The fixture is then placed on a conveyor which will carry the PCB through the machine. The conveyor consists of titanium fingers. Titanium is used because solder will not adhere to this metal.

The introduction of RoHS and the subsequent development of lead free solder (which has a much higher melting point than conventional solder), has caused problems for the manufacturers of material used in fixtures. The higher temperatures causes resin burn out which, in turn, compromises the structural integrity of the fixture. This has created a significant challenge to some manufacturers of both the material and fixtures. Recently fixtures manufactures have introduced higher temperature resistant materials to deal with these challenges. A move from FR4 fiberglass to composite materials has already been made.