Electrical test »Boundary-Scan is a valuable addition to ICT, MDA and FPT«

During the production of Printed Circuit Board Assemblies (PCBA) many things can go wrong, even if the process is automated. For that reason testing PCBAs for potential assembly errors is an essential part of the production process. But which one offers the highest test coverage? To find errors that require electrical testing, Peter van den Eijnden, CEO and President of JTAG Technologies is convinced that the most suitable solution is a combination of ICT/MDA/FPT and Boundary Scan.

Generally there are various inspections being performed during the production process of a PCBA – such as Solder Paste Inspection (SPI), (Automatic) Optical Inspection (AOI) or X-Ray (AXI). They detect possible assembly errors, but not all. SPI for example detects if solder paste is missing on certain pads, AOI can detect if components are missing or misaligned or sometimes if they are of the wrong type. The detection of the remaining possible errors requires electrical testing of the PCBA. This is meant to find assembly errors, not errors in functionality. »The last type of errors would require parametric or specification testing«, Peter van den Eijnden, CEO of JTAG Technologies, states. »A simple test that is independent of the functionality of the PCBA is already sufficient to detect assembly errors. For large production volumes this can be done using an In-Circuit Tester (ICT), Manufacturing Defects Analyzer (MDA) or Flying Probe Tester (FPT) which all rely on access to nodes on the PCBA via pins/needles. For lower production volumes testing with these testers is generally not economically feasible due to the price of the tester and if applicable the fixture. For smaller production series therefore a Functional Circuit Test (FCT) is often used.«

The use of Surface Mount Devices (SMD), in particular Ball Grid Arrays (BGAs), makes it more and more complicated for the ICT/MDA/FPT testers to get physical access to the PCBA. »Consequently the fault coverage of these tests reduces and with that the quality of the end product«, van den Eijnden points out. »At the same time the complexity of particularly digital devices also increases continuously. For example System-on-Chip devices (SoCs) nowadays contain the logic for which traditionally one or more boards were needed. This ever increasing complexity complicates the development of functional tests and increases the cost of its development. Also the fault coverage of these tests as well as good diagnostics of these tests decreases resulting in longer repair times and expensive bone piles.« The effect is shown in figure 1 where the red line shows the reduction in fault coverage from traditional testers when the amount of SMDs on a PCBA increases. »In both cases JTAG/Boundary-Scan can be used as a valuable addition«, the expert states. »With ICT/MDA/FPT JTAG can help to again restore the fault coverage of these testers and with that increase again the quality of the end product. In functional tests JTAG can help to simplify access to and control of device pins enabling better and automated diagnostics. This helps to reduce the cost of test development and shortens repair times. Thus saving costs in repair and avoiding large bone piles.«

The blue line in figure 1 shows the increase in the test coverage realized by JTAG when the amount of JTAG access on a PCBA increases. Combining JTAG with traditional testing then results in a higher test coverage for all types of boards. JTAG Technologies co-operates with several ATE companies to enable optimal use of the customers ICT/MDA/FPT/FCT systems. Together with the tester vendors JTAG has developed special versions of its hardware and software which allow a seamless integration of JTAGs tools in their test systems and a maximum exploitation of the combination. For example, the JT37x7 DataBlaster for Digitaltest. Special additions to the software allow for the combined use of Boundary-Scan with the parallel pins of an ICT or MDA or the probes of an FPT facilitating a maximum exploitation of the combination. JTAG Technologies’ PXI solutions, optionally with special pull-though pods (eg QuadPod / VPC)for mass interconnect systems, and 19” rack-mountable solutions (eg JT 37x / RMI) fit well in the instrument rack of an ATE system. Together with JTAGs software for various platforms like LabVIEW, LabWindows, testStand, C, C++, C#, .NET, Visual Basic these provide for a powerful Boundary-Scan extension for an FCT system. A third solution for integration is provided by JTAG Technologies’ JT 5705/FXT fixture module. This can be mounted on various carriers for easy integration in fixtures.