Posted on 21 Jan, 2016 by Neil Sharp
In a previous post, we discussed the challenges facing OEMs in PCB assembly and how to overcome them. This time we will look at box build assembly. When creating a box build all of the complexities found in PCB assembly still apply - but there is a lot more to consider as well.
A box build can mean many things, from a printed circuit board (PCB) in a small plastic enclosure, connected to a user interface and display, to a complete industrial machine with tens of thousands of parts and multiple sub assemblies.
Therefore, the potential issues you may come up against will vary, depending on the complexity of your product.
However, in this post we will discuss some of the common problems that occur when assembling any kind of box build product.
Sourcing an enclosure
You essentially have two options when selecting an enclosure for your box build assembly: an "off-the-shelf" version or something more bespoke. If you go down the first route, there are plenty of vendors to choose from, offering generic enclosures in a wide variety of materials and finishes. The benefits of choosing an off-the-shelf enclosure tend to include:
- Lower unit price
- Reduced minimum order quantities
- Increased availability
However, you will, of course, be limited to a certain degree as the enclosure won’t have been designed for your specific purposes. Therefore, it’s crucial to ensure that you choose a model into which your PCB or PCBs can be fitted securely and that any additional electronics (displays, connecting cables, fans, LEDs, etc.) won’t become trapped when the front and back halves are joined.
Another factor to consider is whether the design will allow you to carry out routine maintenance. The last thing you want is for a product to be rendered obsolete because it’s too difficult to carry out service repairs, for example.
You should also test the assembled box build out in the field - for example, by subjecting it to a soak test or stress screening - to ensure it can withstand the conditions that it will be placed under during its lifetime.
If you choose to use a bespoke enclosure, many of the issues outlined above will not be relevant, as it will have been designed to meet your specific needs. Your PCB or PCBs will slot easily into place, and there will be sufficient space for other internals, to avoid items becoming crushed or putting pressure on one another.
Similarly, the enclosure will have been created with the right attributes for the environment into which it will be placed.
However, there are a number of potential problems. For one, a bespoke enclosure is likely to be expensive, often requiring several thousands of pounds in upfront tooling. And, once you have ordered one from a supplier, you need to be able to ensure that it will continue to be available so that you can ensure your customers get high-quality products within their specified timeframes. Designing your box build with procurement in mind will help ensure that the components you require remain available throughout the lifetime of your product.
In addition, a complete set of drawings for the enclosure, with acceptable tolerance levels and clear guidelines when it comes to quality standards, must be created to avoid ambiguity at the goods receipt and build stage.
Documentation and version control
Poor documentation and lack of data control cause delays in manufacturing your box build and often result in an incorrect or inferior product. Sometimes it can be easy to let paperwork fall to the wayside – but you have to make it a priority.
BOMs, CAD drawings, Gerber files, software and any other key pieces of data must be revision controlled and managed correctly. Any amendments that do take place during the build should be controlled through a stringent engineering change note (ECN) process.
It’s far easier to identify problems when you have a clear trail to look back on – and you are likely to save valuable time and money in the process.
Any drawn items, such as bespoke labels, enclosures or metalwork, should have tolerances and finishes clearly specified. Leaving these things open to interpretation can cause problems with assembly or quality control later.
Test is not something you should carry out as an afterthought - it should be at the heart of your manufacturing process; something you do as you go along. Test provides you with the assurance that your final product will work when your customer takes it out of the box - that’s an element of confidence not to be underestimated!
As we mentioned earlier, you may want to subject your box build to a soak test or stress screening. And you should also test your individuals PCB or PCBs. The most popular test methods used in electronic PCB assembly are boundary scan, in-circuit test (ICT) and flying probe.
The complexity of your product, the demand, and your budget will all be factors when considering which option best suits your needs - and there are pros and cons of each. In addition to board level tests, you should consider if additional "power up" or "functional" tests need to be built into your manufacturing process.
Box build assembly can vary in its complexity but, regardless of how many components make up your particular product, there are a number of common problems that OEMs face again and again. From sourcing an enclosure, to documentation and version control and, finally, test, there are some steps you can take to ensure that when the product reaches your customer, there will be no complaints!
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