Tuesday, February 15, 2000
Low cost bench top memory module test handlers has been around since 1990. As of today, module handlers are mostly using the conventional contactor fingers at the test site. These 1.5 inches long contactor fingers (gold plated beryllium copper) together with the tester transition board causes impedance distortion and signal degradation during high frequency testing.
The next generation memory modules like PC133 DIMM, Rambus RIMM, and DDR DIMM will all be running at higher frequency. The high frequencies render the existing memory module handlers unusable. There is an urgent need for a low cost and reliable memory module handler that will handle high frequency testing at 133Mhz, at 266Mhz and even at 800Mhz.
Back in early 1999, CST did a survey with the memory module manufacturing industry. Memory module manufacturing managers were asked to rank the importance of features on their handlers. The information opened our eyes.
* “Simple-to-use” ranked at the top of the list. Manufacturers have hard time hiring qualify technicians. As a result, most of the setup and usage of the memory module handler falls onto the line operator who has only a high school diploma. They basically wanted no button, no learning curve, no setup and no adjustment when they change between the many types of module everyday.
* They want Reliability and no maintenance. Their major concern is downtime that causes them to miss schedule and lose money. They want the machine to be a workhorse with durable and reliable parts.
* They want us to take away the conventional test contactor (beryllium copper fingers) not only because it causes high frequency measurement degradation, but also for the high cost of replacement.
* Manufacturers also want the fastest handler for efficiency. They just want most “bang for the buck” to justify their investment.
* Static charge, scratch, and stress on the module under test are also high concerns on their list.
* Surprisingly, cost of the handler is not of major issue in comparison to throughput and reliability. Manufacturers seem to be looking for productivity as the number one factor.
MEMORY MODULE HANDLER COMPETITIONS
Currently, there are several memory module handlers on the market. Survey of users unveiled several unfilled areas:
* Users are tired of the difficult procedures in changing over from single side to double sided memory module and vice versa. They want a fast and easy way of changing over.
* Most handlers on the market cannot test module that has capacitors or resistors on the reserve side. Problems also arise when testing module with uneven bottom side.
* Handlers have problem when testing thin profile modules, it causes it to drop unevenly and fool the platform sensor.
* When the output-drop is too high, it damages the other modules already in the bin.
* Users found that sometimes contactor misalignment or mismatch with tester adapter causes intermitting and fall out in the testing. Besides, contactor pins are too easy to break and too expensive to replace.
* Due to the tight pin-to-pin pitch on the Small Outline DIMM module (SODIMM), there has been no sure handling solution for them.
Apparently, there is still a wide open replacement market for an automatic module handler that can overcome all these problems.
The second problem is Intellectual Properties. Since memory module handler has been around for the last 10 years, one has to wonder if any patent was filed on some of the technologies. A careful study uncovered a US patent specifically on memory module handler. After detail study of the documents, our legal counsel had given his advice and the green lights to go ahead.
RESEARCHING AND TESTING OF NEW IDEAS
In order to overcome the conventional contactor, our engineers looked at using a direct test socket plug-in at the horizontal position. It does not only solve the contactor problem, it also clears the test ambiguity between manual test and automatic handler test since the same socket is being used. However, the anticipated question is “how often do I have to change socket?” The engineers knew that they had to proof it.
The commonly available Yamaichi 168pin heavy-duty DIMM socket is used. The manufacturer specification allows 10,000 manual insertion cycles. A special fixture was built to horizontally punch the memory module into the socket and then withdrew it gently. The insertion continued until the module failed the test. The result was a surprised 200,000 cycles. Similar result was also obtained with the 144pin SODIMM sockets. The engineers repeated these tests and the result was consistent. Their explanation was that the Yamaichi socket would last a whole lot longer when the insertion force is regulated and no jerking was applied like the case of hand insertion. With the result on record, the engineers concluded that the socket would work for more than 100 days in the normal production environment. Together with the socket receptacle to allow quick replacement, it would be a much more cost-effective method when compared to the conventional contactor.
In order to fulfill the reliability requirement of the new handler, the engineers were also told to “over design” all the critical parts. All parts in contact with the fiberglass PCB were constructed with hardened material such as stainless steel, plated brass and nylon. All moving joints were on bearings for long lasting. Vigorous tests were also applied to gauge wear and tear of the parts.
Module Manufacturers also had their question on difference between a conveyor belt system and a direct drop output system. A complex analysis based on engineering data was performed. The conclusion was that a properly designed conveyor system out performs a direct drop system by the margin of 3 to 2. While the direct drop system required seconds of mechanical settling time, the conveyor system can output modules faster and safer.
The size of future modules was also a major design criteria. A thorough discussion with the JEDEC memory module committee (the standard setting body) and the socket manufacturers concluded that modules will not likely be more than 5.25 inches long and 1.7 inches height in the next 5 years.
The ROBOFLEX AUTOMATIC DIMM HANDLER
With all the considerations settled, the result was the birth of the new RoboFlex Handler.
The RoboFlex Handler has a vertical input tray hosting the modules to be tested. The modules are then dropped one by one onto holding rails. A pusher-system grabbed hold of the memory module by the notches on its two sides