Homebrew PCBs

The ability of a board to withstand the stress of repair depends upon the back side treatment of the original copper foil.  FirCopper foil can be made by electroplating it on large stainless steel drums or rolling.  The best technique for developing  adhesion to an epoxy board was a nodulated copper that was overcoated with a brass alloy as produced by Gould Electronics.  My understanding is that the bulk of the foil was plated with a fine grain structure on a large drum, peeled off, and passed into a second copper bath with different plating conditions which produced copper nodules.  A third bath plated a very  thin brass layer on top of the nodules.  Cross sections and some electron microscope work seemed to support this, but no one has to my knowledge ever released the details of their process.  The copper nodules provided a mechanical interlocking as well as increased surface area for a chemical bond.  Go to 

http://www.gould.com/pr.htm

where you will see a nice electron micrograph of the bottom side of their foil.  

This is obviously an expensive process so other foil manufacturers in an attempt to get some of the business began looking for less expensive methods.  Some just plated the brass alloy, others just put on a black oxide, none of which provided the peel strength of the nodulated copper.  From just looking at the finished board it is very difficult to tell one foil from the other.  If you look at the bare epoxy and know what to look for you can see the print of the copper nodules on a board made with Gould foil.  Boards made with other foils have a much smoother epoxy surface. 

As for the overly crimped leads, this is probably a fix for a portion of the assembly process that was giving them trouble.  Components can be nocked out of position by a number of things, insertion of other components, handling, and the solder wave itself.  If you have the clearance around the pads as on low density and some medium density boards, the easiest way to keep things where you want them is to really bend the leads over.  A production shop really hates rework.

----- Original Message ----- 
  From: Roy J. Tellason 
  To: Homebrew_PCBs@yahoogroups.com 
  Sent: Thursday, July 07, 2005 5:08 PM
  Subject: Re: [Homebrew_PCBs] Newbies vs Oldies


  ...can you give me some idea as to why it is that some boards seem 
  to be so easy to work on (in terms of repairs etc.) where you can unsolder 
  parts,  install new ones and solder them just fine,  while at the same time 
  with some of the same kind of parts it seems that no matter how careful you 
  are you end up yanking the plating out of the hole,  perhaps lifting the 
  trace on one side,  etc. -- using the same tools and methods?

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