Mastering Mixed Assembly Processing

We provide mixed assembly placement, which can often require three operations. These are surface mount (SM), plated through hole (PTH) and for most projects, the implementation of heat sinks, cables or press fit connectors tenable PTH I/0 communications. The advent of high speed designs however, has converted some of these connectors from PTH TSM because of SM's tighter tolerances.

That’s why Design for Manufacture (DFM) has gained increasing prominence as a critical part of mixed assembly placement for engineers working at the design layout stage. Mixed assembly placement needs to be done correctly and that requires consideration of all factors during DFM in order to avoid potentially costly mistakes.

A rigorous analysis and study of SM and PTH placement can prevent problems :

• Be sure SM components are placed first, since the smaller percentage of PTH (10-15%) can be hand-placed later in the assembly process
• Prevent the interference with nearby cables or wires, place your connectors close to the PCB edge
• ensure that tolerances are tight and secure on solder, AOI, pick and place and all assembly equipment
• Be aware of any components that have heat sensitivity and make sure they are protected with the right wave solder equipment
• Be proactive in mitigating possible SM and PTH problems by thorough planning at the CAM stage
• Pay close attention to mixed placement assembly issues associated with lead-free components as these require special handling to avoid any thermal problems

An effective DFM plan includes these important factors and many others that need to be put intpractice and maintained. Rigorous planning at the DFM stage insures that elements such as bifurcation are done accurately even in an environment of numerous restrictions. These restrictions can pertain to a variety of issues including mechanical, height, or those associated with wires, chassis or cables.