Posted on 04 Jun, 2015 by Russell Poppe
Outsourcing electronic printed circuit board assemblies (PCBA) is usually a simple and well defined process: hand over the gerber, CAD and a bill of materials (BOM) and away you go. Box build, or top level assembly – or system integration, whatever you want to call it – can be less well defined.
A box build can mean many things: perhaps a PCBA in a small enclosure, or a big cabinet full of wires, or a complex fully integrated electro-mechanical system with electronics and pneumatics.
So what are the basics you need to consider to get an accurate quote and help the build process go smoothly with your electronic manufacturing services (EMS) partner?
The first thing the EMS provider will need is a BOM. This needs to at least include all the main components and should clearly define what materials the EMS provider will source and, where appropriate, what will be "free issued" from you.
Think about what to do with the smaller items: the nuts and bolts, washers, tie wraps, heat shrink, adhesives and so on. Are you going to define these, or let the supplier decide? The same can go for wires and their identifiers. While these are often considered consumables, bear in mind they still have a cost and need purchasing, so must be defined somewhere to avoid unexpected cost increases and/or production delays.
Component drawings, particularly for "drawn" or bespoke items, should have tolerances and finishes clearly specified. Leaving these things open to interpretation can cause problems with assembly or quality control later - it’s best to specify exactly what you need.
Provide 3D CAD models if possible, as this helps to visualise how the product goes together. Many CAD packages offer free drawing viewers, and those more advanced EMS providers will have CAD packages themselves to help convert those drawings into build instructions and update the drawings if required - in an agreed and controlled way of course. A layout drawing showing where major components will go - routing of cables and so on - should be included. This might be important to you for servicing, for example, or for design compliance reasons, but wouldn’t necessarily be obvious to your EMS partner.
Of course, ideally you will have detailed build instructions available, particularly if it is an existing product already being manufactured. However, this is not always the case if a product has been manufactured "in house", and for new products some systems are so complex that it is challenging to complete a design on paper, or even in 3D CAD.
Sometimes an element of design and development has to happen as the first products are made. When a large amount of labour, space or specialist tools are required, it can make sense to outsource prototype builds rather than build them in house. It also gives your assembly partner a chance to learn about the product and hit the ground running when full production starts. Naturally you’ll need to choose an EMS supplier that can assist with this development rather than just "build to print".
For electrical systems schematics (circuit diagrams) will be required. The manufacturing partner should decide on the best build method - e.g. point to point wiring or pre-prepared cables/looms - and produce cutting lists accordingly. Again, provide these in an electronic format if possible.
A sample unit is always helpful, and can be the main source of information if the drawings are incomplete. In this case you’ll definitely need a provider that can engineer and create the drawings for you to ensure consistent builds in future.
Let your EMS provider know the size and weight of the unit. This is important not only for shipping but also storage and handling through the build process. You also need to consider how you need the finished product packed and transported; do you need special boxes or a standard shrink wrap and pallet, for example?
Last – but certainly not least – think about test. For electrical systems you should at least specify basic electrical safety testing - e.g. earth bond and flash tests. Do you want to do some functionality testing as well, or perhaps factory acceptance testing by your staff before shipment to an end customer? Or is a visual inspection sufficient? Seek advice from your EMS provider if required, as they will have the knowledge and experience of what works best.
Outsourcing box build assembly inevitably requires close cooperation between customer and suppliers, and does tend to be an evolving process as a new product goes into manufacture. Providing the right information up front ensures you’ll get to start from a good place where everyone understands what is required.
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