RushPCB Mixed Assembly Placement

Some assembly houses work well with either Surface-Mount-Devices (SMDs), or with Pin-Through-Hole-devices (PTHs). However, Printed Circuit Boards (PCBs) that are assembled with a mixture of both SMDs and PTHs, require special handling.

Does your PCB Assembly House work well with this mixed assembly?

SMDs and PTHs each use different soldering techniques.

The SMDs can be assembled onto the PCB using reflow soldering, or they can be wave soldered.

In the reflow process, a solder paste is applied to the solder pads of the PCB, using a screen printing process, and the SMDs are placed on the solder paste. Then the SMDs and PCB are both heated, reflowing, or melting, the solder, which connects the leads of the component to the pads.

Instead of reflowing a solder paste, a wave of solder can be used to connect the SMDs to the PCB. However, the SMDs have to be glued to the PCB first, or they may fall off the PCB as it is turned over, and the wave of solder would wash off any remaining SMDs.

Pin-Through-Hole devices, after they are inserted into the holes, require wave soldering to connect them to the PCB.

When a mixture of both surface-mount and through-the-hole-devices are used on the same PCB, several steps are needed for soldering:
1. SMDs are reflow soldered on the "component-side" of the PCB.
2. On the "solder-side", the SMDs are then glued in place, without soldering.
3. PTH components are machine inserted, with their leads through the holes, from the component-side.
4. Special handling components are inserted into the PCB at this time.
5. The solder-side of the PCB is wave soldered; soldering the SMDs glued on the solder-side, the leads of the PTH components, and the special handling components, all in one step.
6. The board is tested.

Issues that may need to be addressed before submitting the PCB for manufacturing:
o PTH devices need more room on the PCB, to allow maneuvering of the insertion machines.
o Thermal profile issues should be considered when lead free techniques are used in manufacture.

The expertise encountered at RUSH PCB Inc., with all three types of assembly, SMD, PTH, and mixture of both SMD and PTH, makes Rush PCB a good choice for assembly.