[HH] On MicroSD Problems - Strange Tale of Middlemen, Resell Vendors that cover lower quality die chips in their own brand plastic skin

[Phil C.]

Found this article when researching what brand of microSD card to buy, the
author found some irregularities in some Kingston memory, then went to a
Chinese flea marketplace to buy up all kinds of samples and tested them
electronically  and also  chemically dissolved the plastic coating to see
what was inside:

http://www.bunniestudios.com/blog/?p=918 


Short Excerpt from the article:

Here are the most interesting “high level” results from my survey:

•  The “normal” Kingston cards (samples #2 and #3) were all direct Toshiba
OEM cards (MID = 0x000002, OEMID = 0x544D (ASCII ‘TM’, presumably for
Toshiba Memory)). 
These cards employ Toshiba controllers and Toshiba memory chips, and seem to
be of good quality, and thankfully the only ones that were sent on to chumby
customers.

•  The irregular card (sample #1) uses the same controller chip as the
outright fake (sample #4) that was bought in the SZ market. 
Both the irregular Kingston and the fake Kingston had low serial numbers and
whacky ID information. Some of these cards experience some difficulty in
normal operation. I still hesitate to call Kingston’s irregular card a fake
— that’s a very strong accusation to make — but its construction is similar
to another card of clearly questionable quality, which leads me to question
Kingston’s judgment in picking authorized manufacturing partners.

•  The irregular card is the only card in the group that does not use a
stacked CSP construction. 
Instead, it uses side-by-side bonding.

•  The only two memory chip foundries in this sample set were
Toshiba/Sandisk and Samsung. 
Note that Sandisk and Toshiba co-own the fab that makes their memory chips.

•  Samsung’s NAND die — the most expensive part of a microSD card — is about
17% larger than Toshiba/Sandisk. 
This means that Samsung microSD cards should naturally carry a slightly
higher price than Toshiba/Sandisk cards. However, Samsung does get to offset
that against the ability to diversify the same die from microSD packages
into street-packaged TSOP devices, and they also don’t have a middleman like
Kingston to eat away at margins.


Overall, the MicroSD card market is a fascinating one, a discussion perhaps
worth a blog post on its own. I’d like to point out to casual readers that
the spot price of MicroSD cards is nearly identical to the spot price of the
very same NAND FLASH chips used on the inside. In other words, the extra
controller IC inside the microSD card is sold to you “for free”. 

The economics that drive this are fascinating, but in a nutshell, my
suspicion is that incorporating the controller into the package and having
it test, manage and mark bad blocks more than offsets the cost of testing
each memory chip individually. A full bad block scan can take a long time on
a large FLASH IC, and chip testers cost millions of dollars. Therefore, the
amortized cost per chip for test alone can be comparable to the cost of
silicon itself.