Homebrew PCBs

I did a little experiment with shrink film. In case you do not know
what that is, it is the clear wrapping that you see see on boxes like
software or in grocery stores wrapping small boxes of soap or shampoo.

I was thinking about different ways of securing the mask for
photoresist experimentation. The usual ways are a sheet of glass or
using a vacuum frame of some kind. Neither of those I have immediately
handy. However I got to thinking about shrink film and I wondered if
that would work.

Last night I scavenged the shrink wrap off a box that I had to do some
experimentation. You do need some kind of a heat sealer to be able to
form a pouch. Initially I folded over the wrap and sealed one side. I
tried a heat gun I had, but that did not work too well. The wrap did
not shrink evenly and usually tore. I ran out of scrap shrink wrap,
before I could continue experimenting.

Fortunately where I work has a warehouse and I was able to get several
feet of fresh heat shrink.

This time I tried my laminator. My laminator has two settings and I
set it to low.  Initially I was hoping I could just fold the wrap
over, run it through and have the edges sealed automatically. However
this did not work. The seal just shrunk up over the board.

On the second attempt I heat sealed all the sides  and made the seal
very close to the edge of the board.. This worked too well. The wrap
did not have a way for the air to bleed of, so there was a nice bubble
of air trapped over the board.

On the third attempt, I poked a small hole in the wrap with a needle.
This worked much better. The air could escape, the wrap shrunk up to
the edges of the board and pulled the wrap very tight over the board.
A piece of paper I put on the pcb to act as a dummy mask was pulled up
tight against the board.

It is not perfect at this point. I still see a little bit of ripple in
the plastic, so I am not sure if I can get it flat enough to be usable
for securing a mask. I just used a piece of paper as a test mask, but
I will be trying  a real mask later.

Still I thought I would share this, so others could try it out. While
not as good, you can get some stretch out shrink wrap on containers
you already have.