There are many ancillary services available for printed circuit board assembly, and taking advantage of "one-stop shopping" from contract manufacturers (CMs) for these services can help reduce cost or lead times.

The types of services, and how well they are done, vary widely from one manufacturer to the next. Here are a few to look for:

Cable & wire assembly

Cable and wire assembly is one of the most commonly offered services. A CM should have tools for cutting and stripping both ribbon cables and wires and the ability to handle a wide range of connector types including crimp-on connectors, press-on insulation displacement connectors (IDCs), backshells and over-moulded connectors.

Skill with different strain relief techniques is essential for reliability of your board and cable assembly. For smaller wires, crimped connectors can include a flange that clamps onto the insulation to provide strain relief. For larger cables, backshells that slide onto the cable and tighten over the connector are excellent in low-volume production. In higher volumes, overmoulding to encase the cable and connector in resin provides a strong strain relief that is also water-resistant.

Custom magnetics

If your product includes a power supply, there’s a good chance you will benefit from custom magnetics (inductors and transformers). Our engineering department routinely creates custom coil designs when we develop systems for our customers. There are a lot of proprietary techniques we can use to reduce size, improve efficiency and limit EMI. Then our production department has the coil winding equipment and training to produce the custom parts.

It is not easy to find a CM that can also make custom magnetics, but CMs who emphasise power supply design and manufacturing are most likely to have this skill. The CM should be competitive on cost and delivery with on-shore custom magnetics suppliers for prototypes, beta runs or low-volume production.

For high-volume jobs, custom magnetics are usually procured offshore but have a very long lead time. A CM with in-house coil winding can start your production immediately while waiting for offshore specialty parts to arrive.

Laser cutting

A carbon dioxide (CO2) laser can be used for precision cutting of a variety of materials used in PCB assembly. It offers great benefits for prototypes and small runs. For example, one of our customers needed a Formex shield cut and folded to isolate a board from its chassis.

20170712_EETA_Formex-shield-esd-tray (cr) Figure 1: PCB assembly with a custom laser-cut white Formex shield, in front of a custom vacuum-formed ESD tray filled with these assemblies.

For high-volume production, we would have had the shield mass-produced using steel-ruled dies. In this case, the up-front investment in the die was not warranted by the planned production volumes (25,000 units). It was much faster and cheaper to program our CO2 laser and cut the shields in-house, producing them just in time to meet the PCB assembly schedule.

Vacuum forming

A vacuum forming machine uses heat to soften a plastic material, and a vacuum to form it to a mould. We use our vacuum forming equipment to create custom ESD packaging for the PCB assemblies we ship to customers. These trays provide better protection than ESD bags, are easier to handle, are made from recycled materials, and are both reusable and recyclable.

We also use the vacuum forming system to create housings and similar parts for customer products. For prototypes and low volumes, it’s fast and cost-effective for us to create a mould from low-cost materials such as wood and produce the final parts here. For high-volume production, you would turn to a specialty vendor of vacuum-formed parts, with corresponding NRE to have a mould designed and produced.

Ask your CM which other processes they can do besides PCB assembly. You might be surprised at the different ways they can help you reduce cost and lead time for your project.

First published by EBN.