I was an EE for over 40 years. And I remember the brass eyelet problem well.
But I think trying to simulate plated through holes on home made PCB is going way too far.
I have been using wirewrap wire to fake the vias. I know you cannot put them under components.
On real PCBs the plated though holds are made on each layer before etching. Then the boards are sandwiched together.
This is just too much to try on homemade PCBs.
The sensitizing solution can be purchased and you can make real plated through holes if you really need them.
But that's too much trouble for me. I only use the TT process to make small quantities of boards for ham radio projects.
Bob Macklin
K5MYJ
Seattle, Wa.
"Real Radios Glow In The Dark"
----- Original Message -----
From: Charles R. Patton
To: Homebrew_PCBs@yahoogroups.com
Sent: Wednesday, January 02, 2013 3:29 PM
Subject: Re: [Homebrew_PCBs] Re: plating holes with an exploding wire
My take is that is for both.
A bit of history that weighs on my opinion. Some 40 or 50 years ago,
one method of doing two layer boards was the use of brass rivets that
were then solder re-flowed. Sounds great and reliable --right? As
happens, this turned out to be an incredibly bad technique. The thermal
expansion/contraction of the board fractured the rivet/solder bond to
the traces and the boards would go intermittent. I was in the two-way
business then and remember resoldering all the connections on boards
done with this technique. I read of other similar stories. Furthermore
the technique really didn't work on more than two layers. The cure was
the move to plated through holes. Both problems were solved.
I have used the method previously mentioned on this list of inserting a
wire through the via and soldering to both sides. I feel this deviates
considerably from the brass rivet problem. The wire is copper and
consequently can stretch with thermal expansion, not breaking the solder
bond, but it adds severe constraints on the layout as vias really need
to be extra to the through-hole parts with enough pad to solder the wire
to, and mandatory for SMT parts as it's generally considered bad
practice to put the via in an SMT pad, anyway.
So my take on this is the use of copper metallurgically bonded to the
foil traces by use of plating yields robust connections that can stand
the thermal cycling. The concept of exploding wire is appealing as the
idea of hot copper vapor moving at supersonic speeds will surely bond to
the foil edges it encounters (two or more) and thereby yield a reliable
"plated" through hole. But I've been a electronics designer long enough
to be skeptical of simple statements. Simple designs could have amazing
ways of failing. So one wire explodes OK, but will the next 1000 wires
do so? I know how to find 1 via that's poor in a sea of a 1000, but how
many people know the techniques? Bad vias will lead to incredible
frustrations. The method developed must be very reliable and repeatable.
Regards,
Charles R. Patton
On 1/2/2013 2:38 PM, Bob Macklin wrote:
>
> What is the purpose of this discussion? Is this for two layer boards
> or boards with more than two layers?
>
> Bob Macklin
> K5MYJ
> Seattle, Wa.
> "Real Radios Glow In The Dark"
>
[Non-text portions of this message have been removed]
[Non-text portions of this message have been removed]