Posted on 19 Oct, 2017 by Russell Poppe
Testing is an integral part of the manufacturing process. It safeguards against defects and faults, so when a customer takes the product out of the box, it works perfectly.When looking to outsource your manufacturing, you need to know that your chosen Electronics Manufacturing Services (EMS) partner has good test solutions in place so that they can produce consistent, high-quality products to your customers’ requirements.
In this blog we highlight the importance of test, and outline the different types of test your EMS partner should offer.
Test versus inspection
Test should not be confused with inspection. During production, products are usually inspected through Manufacturing Defects Analysis (MDA). The purpose is to check that the right components are correctly soldered in the right places. A process of repeatable inspection is essential as it allows for any faults to be found early in the process, reducing re-work.
Inspection can confirm that the parts have been fitted in the right place - i.e. the manufacturing process is sound - but can’t tell you that the finished product works. Implementing a test strategy is really the only way to confirm if a product works. And if it doesn’t work as expected, I’m sure you’d rather it was your EMS partner that found this out, and not your customer.
In-circuit and flying probe
At a basic level, they are types of MDA. They cover the majority of the most common process faults that occur, such as open circuits (e.g. something not soldered), short circuits, passive component measurements (resistors and capacitors) and diode and transistor orientation.
But they also measure the value of components. ICT can provide limited analogue and digital measurements, a ‘vectorless’ test to check the soldering of pins to the PCB through a non-contact probe or plate, and even offers some basic functional testing. And flying probe offers limited optical inspection, which can add coverage for those components that can’t be accessed electrically.
For both flying probe and ICT you will need to provide a Bill of Materials (BOM) and Computer Aided Design (CAD) data, as well as populated and unpopulated sample PCBs.
Typically, you wouldn’t need to use both of these methods. A good EMS partner will help guide you on which will be the best solution for your product.
Boundary scan testing is used for checking the correct connection between large digital devices on a PCB. It uses test logic that has already been built into the digital integrated circuits (ICs) on the board, thereby removing the need for physical test probes and equipping manufacturers to debug and program complex digital circuits.
Boundary scan can be used in tandem with ICT or flying probe, but on a board with multiple ICs, it is more likely to be used as a standalone test method. Implementing this solution does require a tailored software program and the cost of the licence needed to write the program is usually around £3000 but this can increase upwards of £10000 in some instances.
Cost aside, boundary scan is a reliable and quick test that takes just a few seconds and delivers in-circuit levels of test coverage and diagnostics for digital circuits.
Electrical safety testing
On electrical assemblies, electrical safety testing is essential as it helps ensure the integrity of the assembly. It’s essential for any product that uses electricity, and should be carried out as a matter of course.
The simplest form is portable appliance testing (PAT). A product is connected to PAT equipment, which checks whether it’s safe to use and that the relevant electrical components are insulated. For higher voltage products, a flash test should be implemented to check whether the insulators have enough strength for the voltage. A higher than usual voltage is applied and, to pass, it should be able to withstand this stress.
Unlike the test methods above, this one is focused on the design rather than the manufacturing quality. It’s testing to see if the product works as it should.
This should be the final test before the product reaches the hands of the customer. While it adds little to the value to the production process, it does provide that extra comfort - you can sleep easy at night knowing your customers will receive products that do indeed work!
But functional test should never be relied on alone. Not least because if it doesn’t work at this point, there’s not much you can do except start from scratch. And a product can still pass a functional test even if something is wrong at a component level, for example missing and wrong value components can go undetected. This is why we always recommend implementing a robust test strategy, designed to verify each stage of the build process and sub assembly of the finished product.
Test should not be an afterthought. If treated as such there is a real possibility all the hard work and effort put into outsourcing your manufacturing will have been wasted. Selecting an outsourcing approach that incorporates a solid test strategy will help reduce costs, and maximise product reliability. The test options outlined here are not mutually exclusive; they cover different elements of the manufacturing process and, depending on your product, a combination should be implemented. Your EMS partner should work with you to devise the best test strategy for your needs.
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