During my searches on eBay for cheap 512MB PC133 SODIMM modules for my T23 collection, I kept seeing this interesting looking module pop up every so often:
Each seller would claim it to be a PC133 module and a size of 512MB. There's obviously nothing on the module except for the "SMM13375-24299" part number (?) and a label indicating that it's supposed to be from "Silicon Mountain Memory Inc.". Well, if you Google that part number you end up with nothing. Same for Yahoo! and eBay. If you look for "Silicon Mountain" you will find them at http://www.smmdirect.com/. However, if you plug in that part number into their product search, you come up with... nothing. You'd think that somebody, somewhere would have documented this module. Well, here's the scoop...
I finally saw an eBay seller that offered one little bit of information which seemed to prove (to me anyway) that this was indeed what he said it was: a 512MB module that ran at PC133 timings. He said he was selling a module which was removed from a working Apple G3 iBook. Now I know that those systems used PC133 modules AND could accept 512MB modules. So armed with this tiny bit of "proof" I sniped the auction and ended up paying $29 for one. In four days I had my answer. Plugged it into a T23, booted it and BIOS reported 512MB. Ran memtest86+ on it for two complete passes by itself without any errors. Also plugged in a Micron-branded 512MB module and ran both together for another two passes without fails. So I was convinced that it was as advertised. Still, there was something familiar about this module design. After I had a chance to look at it, I realized that I had seen it before on eBay as being from another company; I'll get back to this point in a little bit.
Some of you may have already noticed that this does not look like a regular module. Only four "chips" apperar to be on this board; the big black plastic rectangles. And they do not appear to look like most of the other memory modules that are floating around eBay, Newegg, etc. A few of you will know exactly what this is (Hi, fellow geeks!). This design is called "chip on board" or COB packaging. The usual memory module consists of DRAM memories which have already been placed into standard packages. Some of these package types are noted on this page from Kingston, a well-known memory module manufacturer. Inside these packages are the integrated circuits ("chips") which hold the computer's data. Module makers buy (or make) the individual memory chips and solder them on these small printed circuit board and turn them into completed modules. Since the memory business is a very low profit margin business, and here I'm referring to memories which are currently in high volume production, every effort is taken to avoid extra costs which eats into the bottom line. One such cost is the amount of money that is spent on putting the silicon chips into their individual packages. I don't have an exact cost of what companies are paying now days but even if I guess and say that it cost the manufacturer $0.50 per part, then for the sixteen memory chips that are normally on a 512MB PC133 module, that's $8.00 in packaging costs alone. Some module makers are/were trying to cut these costs and that is what leads us up to what COB is.
COB assembly does away with the individual chip packages and simply places all of the integrated circuits directly on the module's printed circuit board. They are essentially glued into position and the same type of connections are made from the integrated circuit to the "outside world". In industry jargon, "bond wires" are attached between tiny pads on the integrated circuit and to the printed circuit board they are glued to. The same technique is used inside a normal chip package so there's really nothing new going on here. After all of the bond wires are attached then the integrated circuits are covered with the same type of plastic resin which is used in the standard chip packages. Here's an example from the Swissbit Japan web site.
Why Swissbit? Well, that's actually what I received. Even though there's a Silicon Mountain label on the module, the information that I can read from the Serial Presense Detect (SPD) bytes says that the part number is SSN06464P3B42MT-75. Here's a screen capture from the Darkhorse memory tester I used at work:
If you look in the fields marked "Bytes 72-79" to "Bytes 88-95", you will see a string of characters; a part number.
THAT part number, when Googled, traces back to Swissbit. This is the name of the company that I have seen attributed
to these COB modules before on eBay. Looking at the company history in their web site, they started from a couple
of people who were at Seimens. Swissbit was eventually spun off as a separate company. During the time that they made
these PC133 modules, Swissbit used several different sources for the memory. Among them were Samsung, Nanya, Infineon
and Micron. In fact, the "MT" in the part number refers to the fact that Micron integrated circuits are being used.
So what I have here is a Silicon Mountain labeled module, which was made by Swissbit, who used Micron memories!
A Swissbit 256MB SODIMM datasheet