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Topic: 4 layer PCB, homebrew (Read 1 time) previous topic - next topic

tinman13kup

I just did another Digikey order to get some parts to repair some electronics and threw in some nifty ICs, passives and discretes. I've made many single and double layered boards to make tiny boards with good success, but it would be helpful to have 4 layers for some of the more pin-happy ICs. I started thinking on how I could go about this and what I came up with is this;

  I have a double sided 1/64" board, which is of course pretty pliable. I want to sandwich it between 2 single layer boards, likely 1/32" .  Alignment between 4 layers could be an interesting challenge, as well as vias, but I have some thoughts on those already.

  What I'm drawing a blank on is the best way to bond the boards together. Another method would drop the board count down to 2 double sided 1/64", but would need something that would ensure insulating the center  layers from each other.

  Since I'm really into small smd's and relatively small circuits(< 50 parts), most of my circuits are less than 2"x2". 

  Right now my vias are basically, well, you heard of leadless components, my vias are componentless leads. I use copper wire and clip flush and solder both sides.

  I'm working up to doing some BGAs, and not wanting to just by something and send it up in smoke, I'm looking at grabbing a few of of the pile of cell phones I have that met an untimely demise. Just as soon as I find one that the mfg sees fit to publish a datasheet on. Thought I had a MAX77803, but all I can find is it's a 90 ball power chip with loads of features, and that's from Maxim. That's probably fine though. I don't think a BGA 90 is the way to start off.
Tom
It's not a hobby if you're not having fun doing it. Step back and breathe

MorganS

Bond the boards together with epoxy. 5-minute "Araldite" brand is pretty good. The 24-hour stuff is stronger and it gives you a little more working time to align the boards.

Use your vias as alignment points - put a wire in while bonding the epoxy. Just make sure you have at least 3 spaced widely apart.

I would not bother - the commercial services are so good and so cheap these days. The only thing is if you need it in 24 hours, the price per board can go to the hundreds of dollars instead of hundreds of cents.
"The problem is in the code you didn't post."

allanhurst

#2
Nov 23, 2016, 04:24 am Last Edit: Nov 23, 2016, 04:43 am by allanhurst
Building >2 layer boards is a job for specialists, particularly since you need vias to get to the inner layers.

Stick to through and stopped vias - buried vias are dubious in my view. And much more difficult to make.

For BGAs laser-punched microvias are generally used in 0.2mm layers ( pre-preg).

I've designed mobile phones with up to 8 layers.  I gather fast processor stuff these days uses rather more.

Of course with a proper process all vias are either plated or pasted and work fine.

pay your money and have experts build it!

regards

Allan.

ps and the costs of a 'spin' ( ie the build of a new prototype) were in the tens of thousands. Try and get it right!

MorganS

Yes, I forgot that BGA's tend to require Via-In-Pad microvias drilled with a laser because there isn't space next to the pads to add vias.
"The problem is in the code you didn't post."

Boardburner2

Bond the boards together with epoxy. 5-minute "Araldite" brand is pretty good. The 24-hour stuff is stronger and it gives you a little more working time to align the boards.


WOW i thought i was the only one to experiment with this.
I used prepreg glassfibre  (thermal setting.).

China does a very good price/service these days though.

tinman13kup

I was also thinking on just adding a layer of fiberglass and resin. If I can remember, I will grab and try the epoxy first.

I just need to make sure I don't extrude any out my lead holes or it could be difficult to solder them to the outer layer.

Perhaps this weekend I will give it a go. I enjoy the challenge, even if I fail at first
Tom
It's not a hobby if you're not having fun doing it. Step back and breathe

Boardburner2

The biggest problem is getting connectivity between the layers.
I only used power/ground planes for the 2 other layers.

Using through hole pins was unreliable as i could not control where the resin got to which prevents solderability
That was prepreg though  not liquid resin.

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