Insuring assembly reliability and PCB repeatability takes experience and rigorous testing. Indentifying defects that can lead to faults is vital to maintain quality and most often in-circuit (ICT), functional tests can detect them. However some defects such as deficient or excess solder, marginal joints, open power pins or misaligned components will not be detected using this method.
Thermal profiling pinpoints temperature at different zones at the top and bottom in a solder reflow oven and allows you to determine what temperature profile is best suited to your circuit board depending on its complexity and construction. The temperature profile that's right depends on factors such as the number of ground planes on multilayer boards, while the profile complexity is based on the number of components and the density with which they are distributed on the board.
There are two important objectives of thermal profiling: 1. Identify accurate process settings for a specific circuit board assembly and 2. Insure repeatable results by verifying process consistency. An inaccurate thermal profile can cause weak solder joints and can damage components, while failure to verify consistency can cause the PCB or assembly to miss reliability targets.
The most tedious, cumbersome and expensive of all PCB tests is ICT testing. The fixtures required for ICT testing can take four to six weeks to build and cost anywhere from $10,000 to $50,000. What makes it worth the investment is its value in testing high volume runs of mature products. It is capable of checking voltage levels and resistance at various nodes and can accurately detect parametric and component failures and PCB design-related faults.
Testing board operation and behavior involves functional testing during which the PCB is subjected to a series of signals and supply volts. Reponses are monitored at various points to verify that the board is operating correctly. This test is typically specified by an engineer with defined test procedures. It is an excellent method for detecting functional and parametric failures as well as wrong component values.
If your project requires only a prototype, you will probably not want to incur the high price of ICT fixtures and can safely rely on basic flying probe or power-up testing. However for projects involving a mature PCB with a long product life that has been designed for a DFT system, ICT testing is most likely indicated and you will want to pay the high price for this assurance. Faults are found at every testing stage, however, printed circuit boards that are subjected to final ICT testing and pass are sure to perform perfectly.