Strip Testing

Strip Testing refers to the process wherein semiconductor devices are electrically tested while they are still in their lead frame strips, i.e., before they are singulated into individual units.  Prior to testing, however, the devices in the strip have already undergone the lead trimming process for electrical isolation of their leads.

Strip testing promotes parallel testing of multiple units at the same time, increasing test throughput and reducing test cycle time. After strip testing, traditional end-of-line operations are performed, including mark, device singulation, vision sort, tape and reel, packing, labeling and shipping.

Strip testing is also sometimes referred to as 'matrix testing'. However, this can lead to confusion because the same phrase is used by some people to refer to a different (and more conventional) testing process that employs trays or carriers to hold singulated units in matrix arrangement.

Strip testing is a relatively new test process that is not applicable to all semiconductor packages.  In semiconductor manufacturing, assembly or packaging is traditionally kept separate from testing, which is done only after the units have been singulated. Since strip testing requires that singulation be performed only after the units have been tested, it is in effect inserting the test process within the assembly process.  The birth of strip testing, therefore, is a paradigm shift that ended the era of keeping assembly isolated from test.

Strip testing offers many benefits, especially in relation to recent advances in semiconductor manufacturing technologies. For instance, one of the major issues addressed by strip testing is the difficulties of handling very small packages (such as the chip scale packages or CSP's) after these have been singulated. 

Very small packages are difficult to handle, process, and test individually. An integrated assembly/test process involving strip testing keep these packages intact in their lead frame strips for majority of the manufacturing steps, eliminating direct handling of the individual units until they are singulated. 

This reduces the occurrence of handling-related issues like bent leads, package cracks, missing units, ESD damage, and the like. Aside from the more protected environment that the strips provide to the units, strips are also much easier to handle and process than individual devices.

Another advantage of strip testing is significant reduction in test cycle time, not only because of its parallel testing capability, but also because of the more efficient matrix indexing scheme that it employs. A single indexing step affects many units, whereas conventional serial processing will only affect a single unit at a time.

Strip testing has also successfully addressed the high cost of testing products that have short life cycles.  This is especially true for CSP's which, strictly speaking, needs to downsize its package dimensions every time the die is shrunk significantly to keep it in scale with the chip's new size, resulting in very short package life cycles.  Short life cycles present a problem in the conventional test process for singulated units, because every significantly new package style and size necessitates the fabrication of a new set of tools and accessories, such as trays and sockets.

Such retooling and reacquisition of new accessories when an old package changes or a new one arrives is not a problem for the strip-test process, since it uses robotic strip handlers and alignment technology that can be reprogrammed to adopt to the new package configurations.  'Package-independent' testing should in fact be a major consideration of anybody setting up strip testing capability.

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Test Links:  Electrical Test;  Burn-in

See Also:  CSP;  IC Manufacturing;  Test Equipment