Homebrew PCBs

Brad,

You are correct, this is quite a challenging project.

Plated through holes:

If you look at the board artwork in the article, you will find a view 
where they show the overlap between top and bottom patterns. At every 
location where the pads on the top and bottom have traces attached, 
there needs to be a connection between the top layer and the bottom 
layer.  A board with plated through holes has a lining of copper plated 
into the holes to make those connections.  Where there are no plated 
holes, the connection can be made by one of several methods.  The 
easiest is to use the wires that go through the holes. For example, 
where a resistor or IC lead is in the hole, it would need to be soldered 
both top and bottom.  For holes that just make a connection from the top 
to the bottom, a wire can be placed in the hole and soldered top and 
bottom.  I usually make a small stub that is bent over at the end of the 
wire.  I drop it into the hole and solder.  Then I bend the wire the 
opposite way on the other side, and solder.   This is called a "z" 
wire.  Plated through holes are the best way to go, but are difficult to 
do in the home lab.

There are several complications associated with making two sided boards. 
The first, and most obvious, is that the two patterns have to be very 
closely aligned.  This is  required because of the connections between 
the two sizes. The holes must be drilled such that they pass through the 
pads on both sides.  The actual etching process is also fraught with 
problems.  You can choose to etch both sides at the same time, or 
protect one side from the etchant while etching the first side. Then 
reverse the procedure by protecting the first side and etching the 
second.  The second process is tedious, but may result in better 
boards.  It is hard to get both sides to etch evenly, and I frequently 
would wind up with over etching on one side when I tried to etch both at 
the same time.  This is especially true with large boards such as the 
ones in this project.

(Another Harvey)


On 3/18/2016 7:36 PM, 'Brad' unclefalter@... [Homebrew_PCBs] wrote:
>
> Separate discussion.
>
> I\u2019m not planning to tackle this anytime soon, but I have been slowly 
> acquiring parts and am hoping after I\u2019ve gained lots of experience to 
> one day build a Mark-8 replica.
>
> I expect this would be a very challenging project, which is why it\u2019s 
> long in the future.  But I\u2019m always interested, always reading and 
> learning.
>
> Jon Titus, the creator, arranged with a New Jersey company to produce 
> board sets hobbyists could order, similar to the TVT.  Those obviously 
> are ultra rare unobtanium now, however, I\u2019m guessing the presence of 
> circuit board patterns in the construction details 
> (http://bytecollector.com/archive/mark_8/My_Mark-8_Info/Mark-8_Construction/RE_Mark-8_Const-NEW.pdf 
> -- page 25 or so) indicates it was at least possible some hobbyists 
> went and made their own, correct?
>
> I\u2019m wondering \u2013 what differs in etching with double sided projects?  
> And when they say the holes weren\u2019t plated through, does it mean what 
> I think it means (there would be a copper connection between a trace 
> on one side through a hole the component is soldered into through to 
> the other side?).  Not sure I\u2019m understanding how the connections 
> would be made from one side to the other.
>
>