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Tim 'mithro' Ansell 2025-09-08 4:49 p.m.

I just found

@Tim Edwards - Lots of discussion about padrings and such is happening here.

I designed and ordered a PCB layout to let me test COB, even though I don't have a wire bonder yet. But I'm increasingly ready to experiment!

@Tholin - Have you uploaded your PCB layout somewhere?

Not yet

Going to wait at least until the board house has reviewed the layout and declared it manufacturable

Alright, no complaints so far and its mid-production. Hold on.

4:47 p.m.

4:47 p.m.

Here's a preview

Nice!

@Tholin - Where are you getting it manufactured?

JLCPCB

6:22 p.m.

I selected ENIG so all the pads are gold-plated. Hopefully that will be enough.

6:22 p.m.

Its not actually too terribly expensive.

6:25 p.m.

JLC quotes $120 for 100 4-layer PCBs up to 100mm by 100mm with ENIG, which comes down to just $1.20 per board.

But where do you get them wire bonded ?

FWIW - I finally got a contact at JLCPCB, will see if I can get to someone who can help with getting wire bonding offered.

3

I am trying to obtain a wire bonder of my own

6:52 p.m.

https://github.com/AvalonSemiconductors/gf180mcu_cob/tree/main/COB_test_board

gf180mcu_cob/COB_test_board at main · AvalonSemiconductors/gf180mc...

Experimenting with Chip On Board setups for GF180MCU chips, most importantly gf180 Caravel. - AvalonSemiconductors/gf180mcu_cob

6:57 p.m.

Based on the RISC-V core on my multi-project die

6:57 p.m.

Outside of the COB, the rest of the PCB is as simple and bodge-able as possible.

6:57 p.m.

Just in case

Have you ever tried working with a wire bonder?

7:42 p.m.

@stuart and Matt did in the past, and it was... pretty challenging

Well, practice makes perfect, right?

can confirm they are pretty hateful machines

12:32 a.m.

fun while working, very frustrating when not

7:03 p.m.

@Andrew Wingate was playing with some castellated edge boards.

Nice! One power domain?

What's the pitch on those ? 1.27 mm ? or 1 mm ?

I think 1mm but have to wait for what @Andrew Wingate says

Yes, the pitch is 1mm as shown. I hadn't realized how large the ring for the bonding wires was so there's a lot more room than I had thought. All this is a bit of an exploration into what's the best form factor for:

ease of use
easiest for the wire bonders themselves
if you want many of them I am open to suggestions.

tbh that COB footprint I made could be scaled down. The power/ground rings can be closer to the die, I think.

Tholin

tbh that COB footprint I made could be scaled down. The power/ground rings can be closer to the die, I think.

Sounds great. Thank you for the baseline. I am just playing around a bit.

@Andrew Wingate Also see https://discord.com/channels/1361349522684510449/1418540236148838461 thread which has the pad frame and how it should be bonded out.

This whole panel is 100mm on a side. and from what I've seen should fit in the wire bonding machines I've seen.

@Tim 'mithro' Ansell What's the die thickness ? Are they going through thinning ?

tnt

@Andrew Wingate Also see https://discord.com/channels/1361349522684510449/1418540236148838461 thread which has the pad frame and how it should be bonded out.

I am seeing 64 pins? Is that what we should be shooting for. I was under the assumption there were no hard standards and was shooting for something that could cover most use cases while being easy for people to work with. There were also some suggestions for this same kind of thing but with .1" spacing and the ability to breadboard. Is there interest in that variation as well?

tnt

@Tim 'mithro' Ansell What's the die thickness ? Are they going through thinning ?

Not currently planned as it is quite expensive in very low volume.

So around 750um then ?

tnt

@Andrew Wingate Also see https://discord.com/channels/1361349522684510449/1418540236148838461 thread which has the pad frame and how it should be bonded out.

I don't think people can access that thread?

Tim 'mithro' Ansell

I don't think people can access that thread?

I can see it

Same

Maybe just my phone being weird?

@Tim 'mithro' Ansell why not ? It's in #general in this discord.

@Tholin - I would definitely like to have some DIP style templates. I believe @ReJ aka Renaldas Zioma needs that for the z80?

2

tnt

@Tim 'mithro' Ansell why not ? It's in #general in this discord.

Just seems to be some weirdness of the phone client, working now. Sorry.

The current COB footprint is too large to fit a DIP footprint

8:11 p.m.

I’ll need to make a new one

8:11 p.m.

But as it stands, I can’t even test the current one

8:11 p.m.

Still do not own a wire bonder and won’t for a few more months

But, theoretically, should be possible. After all, the dies are of the right dimension to fit inside one of those ceramic DIP carriers.

@Tim 'mithro' Ansell So you want one pad frame but different breakout options ?

Tholin

I’ll need to make a new one

Just for reference, this is what it looks like currently.

8:31 p.m.

That's definitely not bondable. Wires can't be at more than 45 deg.

8:32 p.m.

Ah wait, nm, that footprint is not the die itself, forget it.

I was more making a visual model than anything concrete, just trying to engage some conversation and see if there are opinions so I may gather a consensus of sorts.

Okay, I don’t think it needs to be scaled down much to fit routing to the pins

1

@tnt - I think there are missing traces from the bond pads to the edge pads?

correct, there are no traces on anything

tnt

@Tim 'mithro' Ansell So you want one pad frame but different breakout options ?

Eventually, multiple standard templates for everything and it being someone else's problem

8:48 p.m.

But in the short term, one or two pad frames and one or two breakouts.

For reference, this is what it looks like inside an actual DIP-40 ceramic carrier. https://www.spectrum-semi.com/sites/default/files/pdfs/CSB04079.pdf

Relevant section. I believe I can design a COB footprint based on these dimensions. I also have diagrams for DIP-48 and DIP-64 carriers to reference if more pads are needed. (edited)

1

Done!

4

Well, that works!

3

@Tholin - Cool! What size is that?

12:29 a.m.

@Tholin - What design rules does that end up being?

Its JLCPCB’s two-layer PCB rules

7:38 a.m.

Its basically just a DIP-40 carrier, but on PCB

@Tholin - Link to repo?

Tim 'mithro' Ansell

@Tholin - Link to repo?

https://github.com/AvalonSemiconductors/gf180mcu_cob

GitHub - AvalonSemiconductors/gf180mcu_cob: Experimenting with Chip...

Experimenting with Chip On Board setups for GF180MCU chips, most importantly gf180 Caravel. - AvalonSemiconductors/gf180mcu_cob

Awesome, thanks!

I wonder if you could "drop" the chip in a cut out to make the whole thing flatter, bond wires shorter.....

4-layer PCB, and a die-shaped hole milled out of the top substrate, you mean?

@algofoogle (Anton Maurovic) - yeah, something like that

How would that work with the epad?

@urish - You mean the backside silicon connection? I believe you can still have pads in the hole.

1

Is the back of the die electrically connected, though? I don’t think it was in the Efabless runs (or at least not intentionally); @Tim Edwards ?

No, it should be not. The epad refers to QFN packaging and is also wire bonded.

Btw, I think the hole I was talking about is called a “PCB Cavity”, and there are different ways to do it and different options supported. https://www.pcbway.com/blog/PCB_Basic_Information/What_is_Cavity_PCB_0882350d.html Related: die embedding https://www.pcbway.com/blog/Engineering_Technical/Use_Embedded_Components_To_Improve_PCB_Performance_And_Reduce_Size.html

Yeah PCB Cavity is proper name.

5:36 a.m.

They have an picture on that last page like this

oooh that's interesting re: image sensors, since it'd provide some protection to the bond wires without encapsulation

BTW - People here might be interested in the discussions in #die-sorter as well.

BreakingTaps

oooh that's interesting re: image sensors, since it'd provide some protection to the bond wires without encapsulation

(sorry, I was just directed here by someone chatting about garage phabs and just wanted to say I'm a fan of your videos! I'll go back to being a normal person now)

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BreakingTaps started a thread. 2025-09-26 5:15 p.m.