HDD GURU FORUMS

I'm just throwing this out there to see what you guys think..
Lately i've been getting a lot of shorted out monolithics. The 5v fuse is blown, 3.3v rail is shorted or the controller is fried, strange NAND voltages, high amperage, etc which prevents me from reading the NAND chip. I've had some luck swapping or removing components (eg: fuses, controller, etc) however I still get the odd case where every component sans NAND is removed but the NAND chip's output voltages are wrong. My first instinct is to say the NAND chip is bad but I never see this in TSOP48 NAND.

Ideas????

could be the initial ramp up of power as soon as the device is inserted. crappier power supplies could be the cause, or tighter specs on the discretes in the monolithic not handling variances in voltage very well.

The weirdness in the NAND is .. weird as really it is the same part as TSOP with different clothes. I also wonder how well monoliths handle flexing as some of the traces and bonds are extremely small and some monoliths have quite a bit of flex. Not a stretch to think some bonds are being held together by the package alone.

Interesting stuff, wish I had equipment to delve into it

I'm not really debating the cause of +5v overvoltage, its more 1.8v and 3.3v. I think it would be difficult to kill the memory chip with overvoltage. The fuse and controller are designed to absorb shocks on the 5v rail and fail. The 1.8v and 3.3v rails are handled by the controller so it should be isolated so how are these memory chips failing.

The NAND IC is usually wirebonded @ the back of the drive so I don't think flexing wirebonds would be the cause. Perhaps the front of the NAND chip starting at the end of the USB connector is susceptible to flexing.

To rephrase, how many 100% dead TSOP48 chips do you run into? There seems to be disproportionately high number of monolithic drives with dead NAND chips. The only real observation I can make is the wirebonds on TSOP48 look thicker than monolithic so perhaps they can't handle higher amperage as well? I don't know, if I could work on the NAND IC out of circuit I wonder if it would work.

I cant recall having a dead TSOP48 ever, in hundreds of chips.

I have some TSOP48 dead chip, but it is really rare cases. If you have shorted inside monolith, sometimes can help X-ray photo, you can correlate it with traces on surface and sometimes it is possible cut off traces to isolate some parts of device to remove shorts. But of course it is many work, and client usually do not want pay for it.

I can count the number of dead TSOP48 chips I've had on one hand, easily

I wonder how 3D-VNAND will compare to TSOP48 in this type of reliability?

back on topic, what sort of equipment do you guys use to work on a circuit level with monoliths?

I am thinking some type of milling/decapping might be required, along with.. Infra red? of course decent microscope, probably with video.

Measuring the discreets for in/out spec.. is this hard or standard tools with smaller probes?

For me the problem is not damaging the IC and resistors, everything else is simple.. Its very easy to get inside a monolithic

Very often short mean chip cracked.
Monolithic case is very easy damage with pressure.

jeremyb wrote:.. NAND chip's output voltages are wrong.

What exactly do you mean with output voltages are wrong ?

Arthur wrote:

jeremyb wrote:.. NAND chip's output voltages are wrong.

What exactly do you mean with output voltages are wrong ?

When Vcc or VccQ 3.3v is applied some of the logic goes high to 3.3v
I see bad cases where the logic goes high to 0.7v, 2.4v, etc.