Medical Device Link.

The ever-increasing density and complexity of electronic assemblies has proven to be a mixed blessing for the medical electronics world. While printed circuit boards (PCBs) can now handle an unparalleled amount of duties, companies must also contend with increasingly difficult-to-spot faults not caught during the manufacturing process. New hurdles, including component miniaturization, the development of flip-chips, and microvia (a via [electrical path] that is less than 0.1 mm in diameter between two layers of a circuit board structure) technology, put a strain on traditional methods of human-based inspection.

This has prompted the industry to take a look at their inspection strategies. Evidence shows that alternatives exist to better address these difficulties than traditional in-circuit testing methods. Among the methods experiencing resurgence in popularity are automatic optical inspection (AOI), x-ray, and flying-probe systems.

AOI Systems

AOI systems have as their main advantage an ability to inspect a circuit board without experiencing the fatigue-and the consequent errors-which accompany human inspection. Along with this increased accuracy, AOI systems bolster inspection speed (under a minute for an assembly with up to 100 components and over 1000 solder joints). These systems have a high degree of fault coverage, yet do not need test fixtures, electrical sources, or measurements. This latter characteristic of AOI systems is also their primary weakness. The inability to perform electrical tests limits their usefulness, since a major aspect of product inspection involves testing functionality.

X-Ray Systems

These systems are useful for inspecting ball-grid arrays and other set ups that obscure solder connections on PCBs. More specifically, they excel at detecting badly placed or missing solders. While electrical testing will identify these defects as well, x-ray systems can detect them immediately. Companies can justify the purchase of what are typically very expensive x-ray systems by noting their versatility (they can be used to assist in failure analysis, inspect packaging, etc.). To overcome the lack of depth in x-ray images, systems that can produce 3-D images are now available.

Flying-Probe Systems

Increased density and complexity present an even greater challenge for manufacturers of low-volume production runs and prototype PCBs, who need to conduct inspections more quickly and cheaply than higher volume manufacturers. The declining fault coverage of in-circuit testers (which is a result of this increased complexity) has opened the door to a vastly improved new generation of flying-probe systems. While slower than traditional in-circuit testing systems, flying-probe systems can provide nearly 100% fault coverage. They simultaneously analyze and record results, helping to speed up, and therefore reduce the costs, of testing. On the down side, they cannot provide the kind of comprehensive coverage of in-circuit testing.

Notable Links

Articles of Note