FEATURE TEST & MEASUREMENT
device works as it should, in-circuit testing looks at each individual component to prove that it is the correct type, has been fitted to the board in the manner specified, and that it operates correctly.
IN-CIRCUIT TESTING With in-circuit testing, components are tested independently against a program model containing parameters specific to the component and its functionality. The test is conducted in a structured way, unpowered initially, to test for short or open circuits, followed by the testing of passive components and simple semiconductors. After this, power is applied to facilitate testing of the more complex semiconductors. The strength of this approach is that the faulty or missing component is automatically located without needing skilled engineering analysis. In-circuit testing requires automatic test equipment (ATE). This involves a ‘bed of nails’ fixture built for each project. A bed of nails tester is a traditional electronic test fixture which has test pins inserted into holes in a laminated sheet. These are aligned using tooling pins to make contact with test points on a PCB assembly and are also connected to a measuring unit by wires. A ‘bed of nails’ tester adds additional cost to the test process. However, provided product volumes are high enough, this is seldom a problem. The test program is developed by the CEM in conjuction with the fixture manufacturer and designed around the
28 JUNE 2018 | INSTRUMENTATION
specification for the board design. In-circuit testing is generally very fast, typically taking just a few seconds even for a complex PCBA, and this leads to a lower cost per PCBA tested. It is also a tremendously consistent and comprehensive test that will catch any manufacturing defects and component failures. Although in-circuit testing can
include a degree of functional testing, its primary purpose is to validate each component.
“Of the two types of testing, the preference of Offshore Electronics is usually in- circuit testing since it offers a shorter test time and better faulty part diagnosis"
FUNCTIONAL TESTING As its name implies, a functional test is used to check that an assembly functions as it should. Functional testing is a quality control test typically conducted at the final stage of PCBA production before shipping. Functional testing takes a holistic view
– looking at the finished assembly – and applies inputs and power to ensure the assembly performs its desired function to a defined specification. The test does, however, require each assembly to be able to function independently; you cannot, for example, test an interface assembly if it requires a separate control or power assembly to function unless you test both assemblies simultaneously, or construct
Offshore Electronic’s engineers can determine the most efficient and cost effective methods to ensure that every PCBA is subject both to full validation and
comprehensive testing
a suitable test rig. The test may also depend on additional data regarding the specification of associated boards, or of the finished device. Normally, a functional test only proves that the assembly works. It does not usually detect the presence of faults in parts used as protection elements, which are inactive under normal operating conditions. Furthermore, an assembly that fails a functional test will often need very skilled analysis to identify and rectify the root cause of failure. Ideally, both in-circuit and functional tests should be used to confirm the complete integrity and functionality of each PCBA produced. However, this may not always be cost effective so a decision has then to be made about which method is most appropriate. Of the two types of testing, the preference of Offshore Electronics is usually in-circuit testing since it offers a shorter test time and better faulty part diagnosis.
If a fault is detected, the ATE quickly
identifies the exact problem and the fault can easily be repaired. For functional test failures, on the other hand, faults must be diagnosed using skilled engineering resources. Offshore Electronics’ production and test engineers can work closely with customers to determine the most efficient and cost effective methods to ensure that every PCBA is subject both to full validation and comprehensive testing.
Offshore Electronics
www.offshore-electronics.co.uk
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