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Challenges of testing mobile memories


Wednesday, February 08, 2012

Last month, JEDEC hosted a mobile memory event at 2012 Consumer Electronics Show. One of the presenters was Cecil Ho President of CST and a member of the JEDEC Board of Directors. I recently spoke with Cecil about the challenges of testing mobile memories, and he gave me his perspective from his vantage point at CST.

Test&Measurement Designline (T&M DL):  What's the typical form factor for mobile memories? Why is this packaging choice so attractive?
Cecil Ho: To save precious space, mobile memories come in a BGA (ball grid array) package. They are usually constructed with multiple dies stacked on each other. It is generally called MCP (multi-chip package). The chips are interconnected through bond wires.
 
T&M DL: Are there standard multi-chip packages for mobile memory? How do they differ?
Ho: JEDEC has published several package standards for mobile memory. The packages and pinout are keyed on DRAM technology with some optional pins for adding flash combinations. However, due to the many possible variation of flash technology, different vendors' MCPs can be quite different from each other.
 
T&M DL: Why are MCPs difficult to test?
MCPs combine different kinds of memory technologies, namely DRAM and flash. The conventional test method for the two separate memory technologies are quite different.  The convention method is to use a "two pass" tester and two teams of test engineers for their separate expertise.
 
T&M DL: What kinds of tests need to be done? Why?
Indeed, MCPs test need not be complicated. Since the DRAM and flash chips are already tested by their original vendor, only a functional test is required to detect assembly error and die handling damages.
 
T&M DL: How are MCP for mobile applications typically tested?
Today, most MCP chips for mobile applications are tested with general purpose memory ATE (Automated Test Equipment). It is usually done with a "two pass" test.
 
T&M DL: What are the limitations of this approach?
The memory ATE testers are bulky, expensive, and less flexible. They usually require high levels of engineering skill in maintenance and reconfigurations. Besides, as mobile memories are ge