sorry if i came off unfriendly, i know you only posted your experience, i just added my experienceOriginally Posted by mad_skills
Maybe you're right, i was just saying based on what i've experienced...i used a lot of different chips from different batches and i was surprised as well, that the batches differ so much from each other.
your fried 6 sticks by using high vdimm and voiding your warranty and NOW your thinking about what the problem could be?
man, im sorry for crucial to have you as a customer :P
i dont know what chips they are using, but i can guarantee you that some batches from micron are way more sensitive to vdimm than others.
there was a cellshock customer arguing with me about using high vdimm, he wouldnt accept that high vdimm simply kills the chips after some time...
he was using his cellshock kit together with a crucial kit at high vdimm, and wouldnt believe its the fault of the chips that his crucial kit worked at high vdimm for months, while his cellshock kit didnt. well, gmh isnt gmh, and gkx isnt gkx... there are some batches of chips that seem to be able to run with really high vdimm for a long time, while other batches seem to have a relatively high failure rate already at 2.2v...
i talked to an engineer whos in dram for ages, and he told me there used to be bonding problems. basically take a chip that fails and put it in the oven or heat it up with a heatgun, and voila, itll suddenly work fine again.
there are 2 common ways to bond memory or any chips nowadays that i know off.
youd laugh, i actually didnt know this until i started working at cellshock, but memory chips have their own small pcb too
the package has the solder balls on one side to contact with the memory module, and contact pads on the other side to be connected to the actual silicon chip.
everything i wrote below might be entirely wrong, dont take it for granted
im just sharing what i know, or think to know...
if im wrong with anything i write, please let me know
1. the silicon is placed in the center of the package, belly up
so the contact pads are facing upwards. a machine then solders a very thin gold, silver or copper wire to the contact pad of the silicon, or a small drop which is then pulled quickly and forms a wire. the machine then draws the wire to the side of the package where the contact pads of the package are, and connects it there. there are different variations to this, you can solder the wire on both sides, or you solder it on one side and actually just stomp it onto the other pad and rip the wire off., or weld it with ultra sonic sound etc. in the stomp/wedge case the wire isnt actually soldered, but its deformed and pressed against the pad so it makes good contact. i dont know why, but this method of basically stomping the wire to the contact pad seems to be easier/cheaper in some way. it has slightly worse contact though and is prone to come off or have a working but bad quality contact. this happens really really fast, i think we all saw a clip of a chip getting bonded that way one day, looks a bit like a sewing machine
2. the silicon chip has contact pads that can take solder balls directly.
the chip is then soldered to the package directly... in theory you could even solder the silicon chip directly to the module pcb.
this isnt done on a chip by chip basis btw, you have one huge chunk of pcb, the package, where loads of chips get placed on, they all get soldered to the package or bonded. then the whole thing is submerged in the black plastic/ceramique stuff we all know, after it hardened the whole thing is then cut into small pieces, thats when it finally looks like the chip we all know from memory modules
the black stuff is used to protect the silicon, and, to make sure the heat can be transfaired properly.
blue= actual logic inside the silicon chip = heatsource
noooow, the problem that happened back then was that some of the bond, james bond, wires made bad contact or had come off.
well, the black cermaique stuff keeps the bond wires in place, so they cant really come off... but they arent making 100% contact either.
if you look at it its obvious that a bond wire has a smaller contact surface than a solder ball. smaller surface the current flows through... so... electromigration problems... im seriously starting to think that this is the achilles heel of micron chips or memory chips in general.
another thing about the bond wires is, once they are off, they are off.
theres no way to really fix this... solder has a really neat feature, its still kinda liquid, even in solid state. so even if youd have electromigration on it, its a massive chunk of metal that wont degrade that much that quickly, and, it will rebuild its shape to acertain degree.
its like a water drop, if some of it evaporates or is absorbed by the surface its on, itll still keep the same shape more or less. at room temperatures solder flows very slow, but we are talking about electromigration here which happens very slowly too... so i think solder might actually compensate for electromigration to some degree.
meh, i shouldve checked wikipedia before making my paint drawing, ah well
http://en.wikipedia.org/wiki/Flip_chip
http://en.wikipedia.org/wiki/Wire_bonding
disadvantages of direct silicon solder ball contact is that you need to reroute the traces more in the package/carrier... but if you do that i think you can get shorter traces than by using the bond wire technique...
but the problem seems to be cost, bond wires seem to be notably cheaper...
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