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I was wondering how I could remove the silver (chip?) from the center of this PCB. It appears to be held down by that clear substance (epoxy?). The PCB is small, 2 cm sides (Not sure if relevant but thought I would add).

I've never done this before and was wondering if anyone else had experience with this.

PCB In Question

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    \$\begingroup\$ What is on the opposite side of this object? Pad array? Pin array? \$\endgroup\$ Commented Aug 16, 2017 at 18:51
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    \$\begingroup\$ What does it say on the chip etch? \$\endgroup\$ Commented Aug 16, 2017 at 18:58
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    \$\begingroup\$ Why on earth would you want to do that? The bonding wires/pads are too fine to work with yourself. \$\endgroup\$
    – DerStrom8
    Commented Aug 16, 2017 at 19:09
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    \$\begingroup\$ If you don't know what the goal is of having the micrographs, you should ask the faculty member what exactly they want. The procedure and care needed may depend significantly on what they are hoping to achieve. \$\endgroup\$
    – Makyen
    Commented Aug 16, 2017 at 20:06
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    \$\begingroup\$ @ArmandoPinales Do you have any prior experience in IC die imaging? Even after you've removed the die from the substrate, there are some pretty specific techniques needed to prepare it. \$\endgroup\$
    – user39382
    Commented Aug 16, 2017 at 20:56

1 Answer 1

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What you are looking at it the bottom of a silicon die - the silver is actually pure crystalline silicon (the un-patterned side of the original wafer) which has then been etched to add part identification markings.

Flip Chip Bonding Image Source

On the other side of the die from what you have photographed (actually the top of it), will be the transistors and interconnects. The very top layer of the die will have a series of bond pads. The whole thing is flip-chip bonded to the substrate/interposer either chemically or with a solder-like substance - hence the bottom of the die is on the top after mounting.

The epoxy around the edge is there simply to stop the ingress of dirt and fluids (e.g. water) that may otherwise damage the die. It may also provide some mechanical strain relief to avoid stresses on the die from vibration, etc.

Any attempt to remove it will almost certainly destroy the chip and possibly the interposer, especially as there is no way of knowing how many bond pads are underneath, and how they are bonded to the interposer.

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  • \$\begingroup\$ Are you sure it is the bottom, and not the top? \$\endgroup\$ Commented Aug 16, 2017 at 18:57
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    \$\begingroup\$ You are confusing "IC" with "chip" and "die". You need to polish your terminology, otherwise it can confuse people. \$\endgroup\$ Commented Aug 16, 2017 at 19:11
  • \$\begingroup\$ @AliChen wrote in a hurry. Cleaned it up a bit. I admit it was a tad confusing, but then the top being the underside in the photo is tricky to word. \$\endgroup\$ Commented Aug 16, 2017 at 19:15
  • \$\begingroup\$ No they are not. The usual meaning of "IC" (Integrated Circuit) is an electronic part usable via conventional soldering technology. An IC is a packaged silicon die (or chip), with various bonding to copper user-exposed pads. Bonding methods vary. The package could be a wire frame with bond wires, or could be "flip-chip" with bumps/bonds that go to a SUBSTRATE (PO called it as "PCB"). And of course there are ICs that are just bare die, but with solder bonds that a user can solder directly to a PCB. \$\endgroup\$ Commented Aug 16, 2017 at 19:30
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    \$\begingroup\$ @HotLicks, fine, and sometime ago people were working with phlogiston and aether. In this case the dissonance comes from the fact that the picture shows the TOP of an IC in (likely) BGA package, while the "silver" part is the BOTTOM of a silicon DIE. That's why some terminological distinction should be maintained. \$\endgroup\$ Commented Aug 17, 2017 at 0:01

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