Electronic Design

IC Packaging Process Raises Efficiency And Integrates Test

A packaging process developed by Amkor Technology of Chandler, Ariz., is being described by the company as the packaging equivalent of a semiconductor move from 200- to 300-mm wafers. The company's matrix-assembly-and-test process not only increases the speed with which it can assemble chips into leadframe-based packages, it also enables high-speed, parallel testing of these devices.

The cornerstone of this process is a high-density leadframe (HDLF) format, which enlarges the leadframe strip used to package die to 70 by 250 mm. The new strip more than triples the number of devices that can be handled at one time (Fig. 1).

Taking a 20- by 20-mm LQFP as an example, the HDLF format packs 16 packages onto a single strip, versus just five for the company's prior format. However, the number of devices per strip will vary according to the specific package style. Furthermore, the overall number of devices that can be processed in tandem will depend on the number of strips processed simultaneously. As a result, the new manufacturing process permits as many as 585 IC packages to be assembled and tested simultaneously.

In addition to increasing factory throughput, adoption of the 70- by 250-mm strip as a standard format is important for two reasons. First, it lets leadframe production lines share common wire-bond magazines at the front end of the process. Second, it allows the use of common trim-and-form systems on the back end. These systems are used in a process flow that represents a major departure from conventional semiconductor manufacturing (Fig. 2). Specifically, testing begins just after a strip of devices has been encapsulated and has had its leads plated.

In the new manufacturing process, whole strips of encapsulated devices can be fed to high-pin-count testers, which make it possible to test multiple devices in parallel. When compared with the traditional method of testing packaged ICs one by one, the matrix approach significantly reduces test time. It shortens the indexing time (the time required to make contact with the device under test) as well as the test time per device. Amkor's current test setups allow for testing of up to 48 packages at once.

Along with faster, more efficient assembly and test, the process also uses leadframe material and molding compound more efficiently. Amkor estimates the material cost savings to be about 20%.

To obtain all of these benefits, a number of process changes were required. One was the procurement of a wirebonder that could handle a 70-mm strip. Another was the use of a higher-tonnage mold. The molding process is itself a critical element. In lieu of the hard tooling traditionally employed for individual packages, the new process uses flexible tooling to accommodate quick and relatively inexpensive changes in package styles. To switch package styles, the company simply swaps automold chases (inserts).

According to Scott Voss, vice president of Amkor's Leadframe Business Group, changing automold inserts takes less than an hour, versus approximately two weeks for a hardtooled mold. So far, the company has exploited this flexibility to change more than 25 package types to the HDLF format (see the table). The migration to the HDLF format began with low-pin-count devices and is gradually moving up to those with more leads. In the future, the company expects to adapt laminate-style packages to the format.

Because the benefits of the matrix-assembly-and-test process are maximized when production volumes are high, though, the package styles selected for conversion to HDLF format are likely to be the most popular ones. Amkor manufactures about 1000 package types, of which 400 are leadframe styles. According to Voss, many of these will never be converted to the HDLF because of their low volume.

Customers will additionally need to consider the effect of the new manufacturing process on device testing. The integration of packaging and test requires that testing previously done by either the customer or a third party be brought in-house by Amkor. This requires Amkor to get test programs from the customer, adapt them to parallel testing, and build the necessary contactor boards. The process of qualifying a customer for parallel testing can take a few months, Voss says.

Nevertheless, once test programs and contactor boards are completed, it's relatively easy for Amkor to switch from testing one set of devices to another. In terms of the physical test setup, it's simply a matter of changing contactor boards.

For more information about the process, contact Scott Voss at (480) 821-2408 or via e-mail at [email protected]. Or, contact Patrick McKinney, Amkor's vice president of corporate marketing, at the same number or via e-mail at [email protected].

TAGS: Components
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