How are the layers of a multilayer PCB "glued" together?

[noptical]

Is it that "prepreg" thing I hear about that does this job? Where can one find this stuff?


Thanks! (hope I posted in the right subforum)

 

[Hero999]

Let be be the first to admit I'm no expert here.

As far as I'm aware, it's a resin compound which is very sticky, the boards are sandwiched together and baked at a high temperature to cure the resin.

 

[PCBWING]

Resin layer (prepreg) heat and pressure

 

[Sceadwian]

Google is wonderful.
**broken link removed**
Pre-preg is nothing more than resin impregnated board that's stored cool then laminated under high temperature and pressure, do you really need to do a multi layer board? Something like that might be better to outsource to a job shop that can do it professionally, unless you really want to do it yourself. I've not really seen any hobby level project that can't be done on single or dual layer boards with an occasional wire jumper here or there for trace efficiency. If this is a bulk production thing, outsource it, the time spent finding companies that can do what you want and getting quotes to find one that will do it well at a reasonable price is FAR better spent than the research to do it yourself.

 

[noptical]

Thanks everyone for your responses.

Google is wonderful.
**broken link removed**
Pre-preg is nothing more than resin impregnated board that's stored cool then laminated under high temperature and pressure, do you really need to do a multi layer board? Something like that might be better to outsource to a job shop that can do it professionally, unless you really want to do it yourself. I've not really seen any hobby level project that can't be done on single or dual layer boards with an occasional wire jumper here or there for trace efficiency. If this is a bulk production thing, outsource it, the time spent finding companies that can do what you want and getting quotes to find one that will do it well at a reasonable price is FAR better spent than the research to do it yourself.

I don't care as much for the result as I do for the process. That's what makes a hobbyist right?
As far as I understand, prepregs have low shelf life since they have to be constantly refrigerated until use. What kind of resin do is this? Is it some special resin used only by the manufacturers?

 

[Sceadwian]

As a hobbyist you should know there is no such thing as 'special' It's just resin, it's kept cold to keep it inactive, it has to be used soon because even cooled it will still eventually cure. On a hobbyist scale it would have to be made with a resin that had a LOT of inhibitors in it to prevent premature curing. In a real manufacturing process the inhibitors wouldn't be a problem because even given it's short shelf life it would be used very quickly. The way 'we' can do things is ALWAYS different than the way 'they' can do things simply because the scales are so dramatically different between the two.

As an example, an engineer will take VERY different viewpoints on boiling a gallon of water vs boiling ten million gallons of water.

 

[noptical]

No such thing as "special" however there are things that aren't available to the mortals like us unless bought in huge quantities

Anyway, what methods do they use to impregnate the boards? Do they dip it in resin or what?

 

[Hero999]

Come to think of it, I've used prepreg before but not for PCBs. It was a secret project so I can't say exactly what it did.

The prepreg I used at work was a carbon fibre woven into a textile which was pre soaked in resin and consisted of many layers stacked on top of each other. The prepreg was stored at a very low temperature and had a limited shelf life. We put it in a former consisting of two sheets of shaped metal sandwiched together and cooked it for several hours in a huge autoclave. When cured it's extremely strong and light.

I've never seen the kind of prepreg used to make PCBs, I imagine it's similar except fibreglass is used, rather than carbon fibre.

 

[Sceadwian]

If you're doing this at home, you don't even really need prepreg, it's messy but just epoxy the boards together yourself, you just have to find really thin board material I'm not sure how you'd go about making vias between the boards though it'd probably be pretty messy, which is I gather why they use prepreg in the first place. Just doing a Google search for prepreg I found plenty of companies that make the stuff, send an e-mail out to a few of them and see if they do samples or smaller orders.

 

[noptical]

If you're doing this at home, you don't even really need prepreg, it's messy but just epoxy the boards together yourself

thats what i'm planning to do, now i'm in the process of searching for the proper resin that will also withstand a short reflow process later when the board is done, I don't want the layers to come apart from the heat, that would suck. Also looking for some steel (or other metal) plates to make an ~A4 sized press of a few kg (preferably heated). The through hole plating problem is already solved. I have FR4 laminates with ~0,1mm to ~0,5mm thickness lying around so I'm going to use these.

 

[Sceadwian]

I'd think any general purpose Industrial epoxy would do, they're all relatively heat resistant. A few kg per what? Square centimeter or meter?

 

[noptical]

I'd think any general purpose Industrial epoxy would do, they're all relatively heat resistant. A few kg per what? Square centimeter or meter?

A few kg/m^2, sq^2 would be too much