Testing In Manufacture

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Next comes the functional testing of the product. A functional tester (FT) ensures that the product is working as per the requirements. There are various kinds of functional test equipment. Sometimes you may use a million-dollar machine and sometimes not even a million-rupee machine. It goes like this: If your product is very simple, you can develop a smaller fixture and some back-end signalling for your product. For example, electronic energy meter manufacturers need to check whether the LED displays properly or not when electricity is fed, etc. They want to see the sequence of their product in powering condition as well as in functioning condition. For this, a very small FT which is very cheap can be developed. But if the product is critical, the cost of an FT goes very high.

Functional testers are dedicated testers. That means if you develop a fixture for an energy meter, it can be used for a particular energy meter or board only. This functional testing is cheaper. But if you want a universal functional tester, it will be a huge machine that can test a hundred types of boards. This machine is very costly.

MDAs, also called ICTs (but not power-on ICTs), cost $25,000-35,000. The machine’s cost is based on its pin configuration. If the board has 500 points, an ICT with 500 outputs is required.

ICTs cost minimum $100,000-150,000. For a very good brand, the cost can go up to $300,000. Universal FTs cost million dollars or more.

Automatic optical inspection (AOI) systems (used to detect manufacturing defects) do optical testing only. Sometimes designers in the manufacturing line try to inspect the assembly for component defect with naked eye. AOI system helps to ensure that faults aren’t skipped. It can be desktop or inline type. Desktop AOI system costs $40,000-50,000, while inline AOI system costs $70,000-90,000.

Another machine which the manufacturer may want to use is the flying probe tester (FPT). Its speed of testing is very slow but no fixture is needed—fixture adds a lot of cost. But it needs a program, which is very easy to develop. FPT costs about $150,000.

X-ray testers are very dedicated for ball-grid array (BGA) components. Because an AOI system can’t inspect this particular type of device, a few manufacturers who want 100 per cent testing—as required in critical applications like avionics, automotive electronics and space electronics—use automated X-ray inspection (AXI) testers also. Automated X-ray testers cost $100,000-200,000.

What adds to the cost of manufacturing test?
Testing, once confined exclusively to the end of the line, now occurs at several points to provide greater failure isolation and feedback to the manufacturing process. Process tests such as ICT, AXI and AOI sit at various points along the line to immediately catch process flaws. Functional test, which tests the operation of the system of components, typically resides at one or more points along the line and at the end of the line as the final test of the fully assembled product.

With decreasing component size and correspondingly increasing circuit board density and complexity, many products no longer have access points for the bed-of-nails fixtures used for in-circuit testing. Although AOI and AXI systems continue to become more common and more comprehensive, functional test is used more extensively to find and even isolate faults.

With the need for higher throughput and more efficient production and testing, contract electronics manufacturers (CEMs) and OEMs demand sophisticated test platforms for functional testers that are built on open industry standards.

New approaches to testing
There have been efforts to make manufacturing test cost-effective, simpler and more efficient.

Naresh Kumar, general manager-South Asia Pacific Application Engineering Organization, Agilent Technologies, explains that the cost of a material to be tested is amortised over a certain period of time. To reduce the cost of test, pay-per-use option has come up. Here the payment depends on how you test. For testing a product like Apple iPhone, more features are required and therefore you will have to shell out more. Whereas for a product like USB device, you need to pay much lower than for iPhone. How much you pay depends on two-three parameters: For how much time you test, how many boards you test and how complex are the boards to be tested. The more complex the boards, the more the amount to be shelled out for testing the same number of boards.

Today, most of the manufacturing is done by CEMs. That is, if you design a product today, the boards are manufactured by some CEM which has the full facility to service a hundred customers. CEMs survive on multiple orders. Sometimes there could be big orders, sometimes there could be very low volume of manufacturing. The pay-per-use test system works very well for them. It dramatically reduces their cost of test—while maximising flexibility to test boards in a wide range of sizes and complexities. Let’s say, a CEM has a huge order which requires three months of complete activity and then two months of low activity. In these two months, they hardly spend anything on testing. So they purchase a full-capability test system at a much lower price than a conventional system and pay only for the capabilities they need, only when they use them.

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