Well, the proof is in the pudding as the saying goes. If you
have had no problems with delamination or inner layer
connectivity then it shows your method is ok.
I do recall somewhere that drilling at high speed is more
likely to cause drill smear. It may be that relatively slow
manual drilling inadvertedly avoids most of this problem.
Something to do with heat generated at the drill tip. Higher
RPM means hotter. I think in production 100k RPM is typical.
After reading all the necessary storage and handing of
prepreg I knew this stuff was definitely not suitable for
home use. So yes, liquid epoxy is the obvious answer.
The heating and pressure they use must cause some fusing of
the epoxy layers. They also talk about oxidizing the copper
to black oxide to help epoxy bond to the copper. well
according
http://207.207.205.214/bmr/oxide.htmThey use NaOH/NaCl0 or bleach. Damn, now that's adding yet
more tanks to the PCB station.
Thanks for sharing your methods. Multilayer sounds exciting,
but I've got too many other things to finish first.
Adam
Markus Zingg wrote:
> Hi Adam
>
>
>>Markus Zingg wrote:
>>
>>Drill those two holes so
>>
>>>as you later can insert a shaft? (hope this is the right word for it)
>>>into them.
>>
>>Actually the english word for what you describe is called a dowel.
>
>
> Thanks for letting me know :-)
>
>
>>>6) put a very thin layer of 2 minute epoxy (devcon or araldit is fine)
>>>on both sides of the inner layer. Apply it to the INNER layer and do
>>>it all in one step. The reason to apply it to the inner layer is to
>>>make sure there is glue in the etched away parts. Then put the stack
>>>together again using the two center shafts. Put as much pressure on
>>>the stack from both endes as you can. I use two wooden blocks on both
>>>endes and built a wooden construction that holds two vises which
>>>actually press the stack togeter. I used two vises to have more
>>>pressing area and power. Of course if you have a press available
>>>that's better. Let it dry for 5 minutes.
>>>
>>
>>I have tried 5 minute epoxy on PCB material and it doesn't bond
>>anywhere near as well as professional multilayer panels.
>
>
> Well, I get reasonably well results. Let me put it this way, by doing
> the boards with this method, so far all boards came out well, all of
> them are still working today and perfectly served the purpose of
> prototypes. So, why should I bother?
>
>
>>Professionals bond layers with a special purpose partly cured
>>epoxy sheet called "prepreg". I think they insert the prepreg
>>between layers. Then they press at something like 20kg/cm.sq
>>pressure and heat to 175°C for several hours. The heat completes
>>the cure of the prepreg layers and it develops a super strong
>>bond. Here is a data sheet of found on the web of some prepreg;
>>http://www.rogers-corp.com/mwu/pdf/RO4400dsandfab.pdf
>
>
> I do have prepregs here, but I did not had a press. I first thought
> that I have to build/buy/organize such a press, but then thought to
> give the glueing technology a try. Again, this works fairly well. The
> key point probably is to really only apply a thin layer of glue, and
> to do both sides of the inner layer in one step also applying high
> pressure.
>
>
>>Can you wedge the PCB layers apart by forcing a screwdriver in
>>the edge ?
>
>
> I'm sure that the bonding you get from using prepregs is better, but
> what the heck. It works just fine. I NEVER had a single problem with
> false contacts of the inner layer nor did I had a single non working
> board as of now. The resulting boards are also stiff etc. I don't have
> a reason to improve the process for the purpose I use the boards.
> Since the boards were all useable and are in use I honestly must
> admitt that I did not had the ocasion yet to destroy one of them. I
> think with enough brute force applied a screwdriver could be hammered
> between the layers but again, I don't have a reason as of now to do
> this.
>
> Btw, the tip to use glue came from Mr. Bungard. He told me that this
> "technology" was sucessfully used in a german school so I thought that
> if it works there, I should manage the same. :-)
>
>
>>The only other step you are missing from professional multilayer
>>process is the "epoxy etch back" or "hole desemaer" where after
>>drilling there is epoxy smeared on the innerlayers and can
>>interfere with the through hole plating, so they put the board in
>>a hot solution of potassium permanginate/NaOH which removes a
>>small amount of epoxy. I have no idea if this step is necessary
>>for your application.
>
>
> I heard of this. I think due to the manually monitored and carefull
> handled process of mine - remember, I transport the boards myself from
> one bath to the next etc. and due to the fact that I also take the
> time needed to carefully drill the holes this is probably not such a
> big issue. Might be that the chemistry I use is so good that it still
> works. I simply don't know. All I can say is that so far I never had a
> single board that did not ended up just fine.
>
> Markus
>
>
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