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rigid pcb/flex/ wire bonding

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circuit

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wire bonding pcb

hello, i am looking at an application where in I have a chip in the silicon die form which needs to be wire bonded to the very small pcb (around 3 mm x 5 mm) and then I need to take the signals out to a different board using a flex cable.

The board hosting the chip has to be rigid and cannot be flex. the problem i am facing is, the chip has its pads ( all along one ege) with dimension 81 um x 81 um and the edge - edge pad distance is 3 um ( center to center is 84um). Now I heard that the pads on the board is preferred to be directly under the die so that wire bond can be straight wire. now this means the pads on the board will be separated by 3 um edge-to-edge which is not acceptable for any pcb manufacturer. I checked with many pcb manufacturers and they are willing to go as far as 3 mil ( track space/width). when they say 3 mil spacing everything is edge to edge ?

Now my question is, do you have any suggestions for wire bonding companies in the US. and what are the requirements on the pads on the board. can i move the pads away from the chip so that somehow i can make everything 3/4 mils spacing (the person who was supposed to do the wire bonding said he prefers the pads to be underneath the silicon). or is there a different technology that is there to work at such fine pitch devices ? thanks in advance.....
 

cjkao

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wire bonding pcb pitch

see document page 4
 

edaedaeda

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wire bonding to flex

It seems that someone is making this project harder than it should be...
Ive just completed a wire bond board with the following parameters:

Die Size: 3750 x 2500uM
Die pad pitch: 80uM
Pad distance from edge of Die: 158uM (passivation opening is 4uM)
Pad shape is Hexagonal: 72uM x, 113uM y.

I created the bond pad at 4mils x 6 mils. Placed all GND bonds to Die Flag. (copper plane under die)
And finally all signal bonds were fanned out to 100 mils (3mil trace with 3mil space)
Yes, it is always edge to edge.
The package for this part is a 104 pin QFN with .4mm pitch.

So far there have been no problems with manufacture. Ive also taken the time to have my wire bond person have a look at design to assure that it could be done.

If you have questions drop me a line.
Have a good one,

Eda
 

    circuit

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circuit

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wire bonding on pcb

thanks for your reply. I have met with the wire bonding guy and the arrangement of pads I have on my board, he said it could be done. But I have a question, I want the die to be wire bonded to a rigid board and then use a flex interconnect/cable to transfer the signals to another FR4 board. The issue here is the board hosting the die has to be max size 3 mm x 10 mm. Now this is really miniature and causing problems as far as the pitch of the flex cable which is going to take teh signals out. There are going to 18 signals and I dont see any flex cable manufacturer going to pitch less than 0.5 mm ... and this means i cant accomodate 18 signals in the 10 mm.

> Placed all GND bonds to Die Flag. (copper plane under die)

is this a two layer board ?

Other question is, how good/bad it is to wire bond the die to a flexible printed circuit and use a stiffner at the chip location. And i guess i can just take the FPC to the other FR4 board and use a ZIF connector over there...thanks much
 

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