Initially, in the early stages of PCBA assembly, fixtures were rarely used. Almost all PCBs could pass through the oven directly without the need for any fixtures unless the boards couldn’t withstand heavy loads, such as power boards.
The use of fixtures for reflow soldering became prevalent with the rise of selective wave soldering, coupled with the trend of thinner and smaller PCB sizes. Therefore, not all wave soldering processes necessarily require fixtures. Here are some conditions under which PCBs can pass through wave soldering without fixtures:
- PCB Design Requirements: The PCB should have at least 5mm of board edge reserved for the wave soldering chain and support when placing PCBA on the feeder rack. The PCB thickness should ideally be above 1.6mm to minimize board bending and solder overflow issues during soldering. The recommended gap between all solder pads should be at least 1.0mm to prevent solder bridging faults.
- Component and Layout Requirements: The types and orientation of SMD components must meet the requirements of wave soldering. Through-hole components must all be designed on the first side, and their orientation must meet the requirements of wave soldering (pins must be parallel to the direction of board travel). Components on the PCB should not be too heavy to avoid bending the PCB due to gravity.
- Process Requirements: All SMD components on the wave soldering side must be taped with red glue to prevent them from dropping into the wave soldering furnace. Some solder pads that should not be tinned (such as button contact lines, gold fingers) are not recommended to be designed on the wave soldering contact surface (second side). If necessary, solder pads that should not be tinned can be designed on the soldering contact surface, but high-temperature adhesive tape that is not easily residue should be used to cover the wave soldering. After implementation, the tape should be removed. However, this practice should be avoided to reduce labor time. It is recommended to use short-legged components for wave soldering to prevent short-circuit faults, with the foot length of each through-hole component not exceeding 2.54mm.