EEVblog #1158 - How To Create PCB Mod Boards

PCB mod boards are useful for a whole range of applications and scenarios from production to upgrades, repair, and hacks.
Dave shows you several examples and talks about creating manufacturing panels for them, along with castellations, V-Scoring, routing, and manufacturability.

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[shana_dmr]

You managed to do whole video about this topic without using the word "bodge", I'm really impressed :D

[wanderinguser]

Only five minutes in & we've got MELF on MELF action! This is going to be good!

[JWH]

Call it what it is Dave. It's a bodge, plain and simple ;)

[urdnal]

Never mind mod boards, what's coming up in the old arcade game scene is custom ICs. Well, not _really_ ICs. They're little boards that replicate the functionality of failed custom so-called hybrid chips. Usually SIP, ceramic substrate, always encapsulated. The two I've got was a video DAC/buffer and the other did audio mixing for music and sound effects.
It was once thought that once these custom components are gone, that's it. Fortunately there's guys out making replacements.

[Stuartrusty]

I know what you mean about repairs/replacements for military and defence. Also some backwards compatibility had to be part of the design of some sub-assemblies.
The company I worked for had to include (as part of the purchase agreement and contract) an assurance that we could repair, supply, maintain or replace everything down to component level for 10 years after date of installation.
Bodge wires and mod boards would be used regularly to overcome very real obselesence issues out in the field.

[pauljmccain]

I love these "how to do it" videos, Dave. One thing to note - some products such as wifi and bluetooth interfaces are designed from the start to be used like mod boards, placed down on your design from trays. Vendor gives pad layout for castellations, etc. I dont know how common it is, but we use one that way! We can use that mod board on a number of different designs, making changes to it independently of the main board.

[kostaskritsilas]

I used to work at Philips electronic in Montreal. We built PCs, and did our own board assembly. Being a high volume shop (~500K motherboards a year, and a similar quantity of VGA graphics card), the standing rule was that one mod wire would force a board re-spin. We would use up existing inventory of PCBs, and the next order would have the new artwork. Somebody internally did the math, and figured out that the manual labour to add a mod wire, and the bottlenecking of the production lines was always a higher cost than the re-spin cost.

Also, after about a year, MELF packages were banned. In our case, they were used for diodes and a few capacitors, and sue to their shape, gave the pick and place equipment (Fuji CP III and CP IV) a lot of problems, and they tended to roll off of their pads when moving down the conveyor line.

[pavlitt]

For panelised thin PCBs undergoing pick and place, it can be easiest/cheapest to break out the circuits from a number of sacrifical panels and glue the panels together until thick enough to be stiff and act as the back support for a panel being populated.

[noakeswalker]

In the UK electronics industry (HP), we used the terms 'kluge' or 'kludge' for an add-on mod like this. Wikipedia gives lots of possible sources for these words dating back even as far as WW1. If a mod is a bit 'kludgy', it generally means it's a bit of a bodge, but it works. The Scottish slang for toilet is 'cludgie' :o) OTOH, a kluge pcb can be a valid way to a nice result, as with Dave's 121GW meter mod here, imho. Thumbs up !

[morgueaunne]

"Board" - the fine line between "Bodge" and "Mod"

[GadgetUK]

Thanks Dave, this is super useful! I recently created a PCB in my last video and the problem I had was getting the PCB fab to cut the castlated edges - what I was missing was the idea of panelising it, and I had no v-scores. That would have helped I think. I will do this in the revision.

[maxheadrom]

Nice video - very important subject! When you were showing the game mod boards, I remembered a design by Koichi Nishida of a Apple II disk drive emulator for the IIc: it fits inside the case perfectly!

[UpcycleElectronics]

Hey Dave(s)
8:48
Upload referenced:

(And for good measure)
Dave's "PCB Design & Manufacture" playlist:

[picklerick]

how can one single human being have so much professional knowledge

[PilotPlater]

Never heard of this outside of a daughter board as part of the initial design for space/layout constraints. Very cool!

[eNodeTG]

These kinds of videos are the reason I still watch YouTube, and pay for it, hope I'm not an unnoticed minority from the parent company perspective.

[kbhasi]

I noticed that with the new background, you get to use those shelves for ephemera you like, while using the library layout shelves off-screen for actual Mailbag items!

[lp]

Since you have not mentioned it: Are these two transistors in a voltage-clamp configuration just like you explained in the previous video? It really seems so.
Was the previous clamp part too expensive, has it produced problems in the circuit, or why was that mod neccessary?

[alynicholls]

at a previous employer we we building 40 small detectors for a large company who has to remain nameless, anyway on a really tight deadline when we went to start assembly the supplier had sent sot23 versions of a particular part, not having a substitute part and not enough time to re order we just used those little adapter boards, in the end it worked out better since battery life improved and sensitivity increased, not mega amounts but noticeable, in fact the "bodge"board became a service replacement when refurb and service was done on older units.

[russgibson]

This what great! If you ever do a follow up, I'd love to see the actual attachment to the original board (I know its just soldering ... but I've learned the hard way about how important technique is, so I'd love to see an example from someplace I trust).

Thanks for the great content!