Tuesday, September 05, 2000
Dram a highly fragmented market
The revolution of DRAM module industry has evolved from the legacy fast page mode, then EDO, till today’s mainstream synchronous dram.
The industry is currently touting Double Data Rate(DDR) DRAM and Rambus Dram as the next generation DRAM standard.
Along with the rapid technological changes, the DRAM market has evolved from its homogeneity into a highly fragmented market, which is driven by increasingly diverse computer memory applications.
The traditional desktop, notebook, server, and workstation markets have taken an unconventional move by offering various memory module designs to fulfill their respective customers requirements in terms of cost, performance, reliability, form factor etc.
Beyond PC market
Beyond the PC market, the state-of-the-art applications for memory includes set-top boxes, routers, sophisticated graphics applications, and a host of other memory-intensive products have further challenged the design and testing of the memory modules.
As the speed of DRAM continues to accelerate and the host system continues to change with constant variation in design and timing specifications, memory testing has also become complicated than ever.
A memory module that works in one system may not necessary function in another and vice versa.
The problem lies with the differences in the systems’ chipset timing requirements. Since the best test solution is to fully simulate the environment of the actual system, motherboard testing seems to be the ultimate memory tester.
But since all systems are different in some way, how many motherboards should one need to run to qualify the module to be good?
There is no simple answer to the question. Different module manufacturers have their own standard ways to test and qualify a memory module.
A motherboard test consists of connecting all the neccessary peripherals to allow the motherboard to power-up , you would need :
- memory module
- ATX power supply
- Video card
- Floppy drive or hard drive
- memory diagnostic sofware
- Monitor for display
Normally most manufacturers will perform a Power on self Test(POST) and bootup thru the hard-disk operating system.
Some other manufacturers would use a low cost memory tester to perform a quick basic test (open/short test) to ensure the integrity of the assembly work while others would run a more thorough and intensive test for all the chips on board.
Some reputable manufacturers would move beyond a step further setting up the memory tester and a range of popular motherboards as part of the complete test procedure. Since no tester can fully simulate the real environment of all the available systems out there in the market, the final and most reliable test may well be on the PC systems.
So, does that mean we should abandon the tester and move straight on to the motherboard test?
Let’s analyze this for a moment. Motherboard test is time consuming and labor intensive. It is not suitable for volume production.
Some of the constrains accompany motherboard test are :
- long boot up time,
- fragile test sockets,
- incapable to pin-pointing bad chip
- no timing adjustment ,
- no safety protection to the motherboard from faulty module that may burn the system etc.
Because of all these limitations, a dedicated hardware testers are still essential as part of the testing process if not all.
Why the need of a memory tester?
Let’s revisit the tester issue !
What type of memory defect can a typical memory module tester capture. A reasonably good memory tester can detect the memory faults such as :
- assembly error such as open & shorts on the solder joints,
- memory cell contamination,
- missing component,
- incorrect SPD codes,
- out of specification chips,
- leaky current ….etc.
There are controversial issues such as trace length impedance, printed circuit board clock delay timing, noise due to voltage overshoot, as well as system integration problems, among many others, which may be harder to detect with the regular test setting. In-fact , even an ATE class tester has no solution to all these issues.
Test engineers at a few world class DRAM manufacturers have long voiced their need for a reliable production tester to replace the cumbersome motherboard test. Their precious feedback and input are taken seriously.
At least one memory module manufacturer has undergone a massive development to build the next generation “memory tester”. As long as there is enough demand, there will be supply. Ultimately, there will be a simpler solution to this complicated problem.
What matter now is who can come up with the right solution first. And that solution, according to those engineers, must have cost, exceptional performance, and proven reliability to be taken into consideration.
By: Daniel Tan
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