TEST & MEASUREMENT FEATURE
A TESTING TIME FOR PCBA RELIABILITY R
The reliability of PCBAs is heavily dependent on how they are tested during and after manufacture. Dave Cleal, technical director at Offshore Electronics, describes the two main types of PCBA tests and explains their advantages and drawbacks
eliability – the quality of performing consistently well –
is at the heart of all electronics manufacturing, but nowhere is it more vital than in the production of printed circuit board assemblies (PCBAs). PCBAs are critical components in the operation of virtually every electronic device from small lamp controllers to large industrial power generation equipment. The dependability of these devices is an overriding concern in many cases with any failure having a serious negative impact on the business. That is why these ‘mission critical’ applications rely on reliability.
The reliability of PCBAs will depend on a number of factors, all of which will have a big effect on the performance of the assembly. These factors include: board design; the specification and quality of components populating the board and any protective coating applied to them; the care with which each assembly is made; the production conditions and skills of surface mount and wave soldering machine operators; and the subsequent handling and assembly of the boards into the finished product. Although it has wide-ranging
implications for PCBAs, reliability is
“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"
The reliability of PCBAs depends predominantly on effective testing
never a given – it depends predominantly on effective testing. This, however, begs a fundamental question: How can those responsible for testing PCBAs be confident that they are conducting the right procedures to detect production or component faults? Several types of testing are available
to PCBA manufacturers. Bare-board testing, for example, involves analysing the PCB before it is populated with components (surface mounting or through-hole mounting of resistors, capacitors, and so on). This ensures the early identification of failures such as shorts (a connection between two points that should not be connected) and opens (a missing connection between points that should be connected) and, thus, results in increased production economies. Once the printed circuit board is
‘populated’ with electrical components and becomes a PCBA, there are a variety of tests that can be undertaken including visual and automated optical inspections, analogue signature analysis and power-off testing. However, there are essentially two types of testing for PCBAs that should guarantee reliability – in-circuit and functional. The primary difference between the two is that, while a functional test simply checks that a
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