Homebrew PCBs

it is nice to see this here.
i have also seen this effect of stronger exposure in the center.
i have used a setup with distance about the same as pcb with.
i used a nitraphot 200W photo exposure lamp.

i think this gets only visible if you have the exposure time on the too short edge.
i never again have seen this error (but i increased distance, made smaller pcb, and had to increase 
exposure time).

the nitraphot is also no good lamp for exposure.

but there is a reason for using a point light source:
if you use some fluorescent tubes you have a wide area of light emitting surface.
if you look at one point at the film/pcb you can see different lightbeams fall on it, from different 
angles. if your film does not perfectly lie down on the pcb it will make a "washed out" edge there. this 
would make the tracks smaller. each pcb has some sort of uneven surface. i think this also depends on 
your overall setup how strong this effect is (and on pcb quality).

a friend of mine uses because of this effect a setup with a daylight halogene bulb.
this bulb is relatively cheap (75eur) and works directly from mains.
but you would need a fan with this, it gets very hot.

this i think is the only reason for using a point source is better.


i have seen some description for making the light of the fluorescent tubes more parallel at think and 
tinker i believe (not sure).


it is fine this setup works fine for you, i only wanted to say that i have also seen the problem with 
stronger exposed center (you also can calculate this) but i found it only happening in "borderline" 
cases.


regards
stefan







18.05.2003 20:52:25, Hans Wedemeyer <hans@...> wrote:

>Mike,
>H'mm as I have pretty good looking boards and can do 5 mil all day long
>!
>
>Here's an example  http://hans-w.com/pcb_harwin_rivets.jpg
>
>I've only been using Round Bulbs of various types for about 27
>years......
>I like the short exposure time and never have noticed the effect you
>menitoned, my largest board size
>is about 6"X7" and it exposed uniformly.
>
>Just what is it about my boards that you think would make them any
>better ? Please explain !
>
>Hans Wedemeyer
>
>
>Mike Putnam wrote:
>
>>  Hans,
>> I looked at the picture of your UV exposure setup. I just wanted to
>> comment
>> that I would never use the round bulb. Use the florescent tubes and
>> your
>> results will be better. I have found that the round bulb tends to give
>> more
>> exposure in the center than at the outer edges. Even more apparent
>> with
>> larger boards.  This is the reason all exposure units sold on the
>> market use
>> the florescent tube. You can compensate somewhat by having the bulb
>> not so
>> close, but this just increases your exposure time. The other bad thing
>> about
>> the round bulb is the heat. This will actually get in the way of your
>> process, depending upon what type of photo etch you are using. I am
>> trying
>> to recall if it was a problem caused to the developer or if it was a
>> consistency problem in the exposure. Nevertheless, I found it to be a
>> problem several years back. If you modify your design to use the
>> florescent
>> bulbs, you will notice a marked difference in detail as well as less
>> exposure time needed.
>> -Mike
>>
>> ----- Original Message -----
>> From: "Hans Wedemeyer" <hans@...>
>> To: <Homebrew_PCBs@yahoogroups.com>
>> Sent: Sunday, May 18, 2003 7:41 AM
>> Subject: Re: [Homebrew_PCBs] How I make my PCBs
>>
>>
>> > Leon,
>> > good advice except for Easy-PC....
>> > I spent full price on that program and found I wasted my money.
>> > Here's what I think of Easy-PC
>> > http://hans-w.com/ezpcbugs.html
>> >
>> > I moved on to EAGLE and have been happy with it. It's STABLE does
>> not
>> > blow up cause me to lose work=time=money.
>> >
>> > A limited version of EAGLE is available for Free, it is limited to
>> two
>> > sided board and size check it out at
>> > http://www.cadsoftusa.com
>> > EAGLE has a VAST library of part and users add parts all the time.
>> > Compared EAGLE parts Library to to Easy-PC  several 1000 to 1
>> >
>> > I put Easy-PC up for sale on eBay but none wanted it. In fact I put
>> my
>> > entire collection of Numberone product in the same auction
>> > Filter program, Easy-PC for DOS and for Windows and the digital
>> > simulator Pulsar. INo one reached my minimum Price of $200 ! It's
>> still
>> > here in a box onthe floor, I think I'll use the disks and CD's for
>> > target practice sometime...
>> >
>> > Here's one thing that is not (was not)( they may have fixed it  by
>> now)
>> > possible to do with Easy-PC for Wndows, in a situation where top and
>>
>> > bottom layers have parallel tracks sections that  overlap, and a
>> whole
>> > bunch of closely spaced via's or other pads, it is not possible to
>> put
>> > the cursor on the trace/pad that I want for move/edit. It just snaps
>> to
>> > the nearest and of course that is not handy at all ! I can turn snap
>> off
>> > but that is not what it's all about.
>> > EAGLE allows ANY pad/trace on any layer to be individually selected
>> even
>> > if they are overlapping.
>> >
>> > Pulsonix used to look like Easy-PC, I think they are the same
>> bunch...
>> > Although Pulsonix used to give the schematic editor away for free,
>> the
>> > PCB layout part is high $$$$ !  That's much like saying "this car is
>>
>> > free, but the special wheel cost $20,000 each "
>> >
>> > I'll get off my soap boix now...
>> >
>> > I make double side board all the time. I used to do it the way you
>> > mentioned, and even wrote a program  for my CNC mill to compensate
>> for
>> > alignment problems.
>> > I found a better way by printing on transparencies and then aligning
>>
>> > them visually, then stapling them together. Then slide the board in
>> > between the transparencies and sandwich the whole lot between two
>> plates
>> > of glass, and place the sandwich between two lamps
>> > http://hans-w.com/setupforexposure.jpg
>> > and
>> > http://hans-w.com/twolampexposure.jpg
>> > Credit for this sandwich idea goes to
>> > http://www.electricstuff.co.uk/pcbs.html
>> >
>> > Alignment between top and bottom is good. Perhaps the greatest
>> problem
>> > I've run into is the HP LaserJet making different print sizes when I
>>
>> > mirror the one side.
>> > I used to worry about getting the printed side of the transparency
>> close
>> > to the PCB, after testing with 5 mil lines I decided there is NO
>> need to
>> > mirror. Using the exposure as I how in my photo it allows me to do 5
>> mil
>> > lines all day everyday.
>> >
>> > Thanks for all the tips.
>> > Best Regards
>> > Hans Wedemeyer
>> >
>> >
>> > Leon Heller wrote:
>> >
>> > >  I've been making my own PCBs at home for about 40 years, starting
>> by
>> > > painting the pattern onto single-sided PCB material using a fine
>> > > paintbrush and cellulose paint, with ferric chloride or ammonium
>> > > persulphate etchant. I used 0.1" graph paper for designing the
>> layout
>> > > then marked the holes with a centre punch through the paper onto
>> the
>> > > copper surface. I even made a couple of double-sided PCBs using
>> this
>> > > technique, by masking off one side, etching the other side,
>> drilling
>> > > it,
>> > > and using the drill holes as a guide when painting on the resist
>> on
>> > > the
>> > > second side. I then masked off the first side with tape to etch
>> the
>> > > second side.
>> > >
>> > > When low-cost CAD software became available (I used Easy-PC from
>> > > Number
>> > > One Systems for years) I progressed to printing 2:1 artwork on a
>> dot
>> > > matrix printer. I then got a local litho platemaking company to
>> > > produce
>> > > a 1:1 positive transparency that I used with a home-made UV
>> exposure
>> > > unit and resist-coated PCB material. When I got an ink jet printer
>> I
>> > > found that I could get reasonable results by printing 1:1 artwork
>> onto
>> > >
>> > > tracing paper.
>> > >
>> > > I now use an old LaserJet IIIp I picked up very cheaply to print
>> 1:1
>> > > onto LaserStar film and expose the PCBs in a home-made UV exposure
>>
>> > > unit.
>> > > I sometimes use tracing paper (nice and cheap), but find that I
>> get
>> > > better results from the LaserStar film. The CAD software I use is
>> > > Pulsonix, a professional package out of the same stable as
>> Easy-PC. I
>> > > regularly use 12/12 design rules, occasionally going down to 10
>> mils
>> > > if
>> > > I need to route tracks between IC pads. Rather than conventional
>> > > positive-resist FR4 PCB material, I usually use something called
>> > > FPC-16
>> > > which consists of a sandwich of compressed paper between thin
>> layers
>> > > of
>> > > fibreglass. It's cheaper than FR4 and much easier to cut and
>> drill.
>> > > It's
>> > > available from Mega Electronics, as is the LaserStar film.
>> > >
>> > > Etching is in ferric chloride. I place the etchant in a small
>> plastic
>> > > food container inside a larger container half-filled with hot
>> water
>> > > and
>> > > continuously agitate the etchant manually by rocking the
>> container.
>> > > Etching typically takes 5-10 minutes.
>> > >
>> > > I'm quite pleased with the results. I intend to experiment with
>> > > double-sided boards by making a UV exposure unit that can expose
>> both
>> > > sides of the PCB simultaneously. With a better printer and vacuum
>> on
>> > > the
>> > > UV exposure unit I think I could get 8 mil tracks quite reliably.
>> I've
>> > >
>> > > heard of other people managing it at home.
>> > >
>> > > Here is an example of one of my PCBs:
>> > >
>> > > http://www.geocities.com/leon_heller/pcb.html
>> > >
>> > > I often use the Pulsonix copper pour facility for this type of
>> board,
>> > > as
>> > > it makes the routing easier. Cross-hatching is better with a laser
>>
>> > > printer, as they don't tend to print large black areas very well.
>> > >
>> > > Links:
>> > >
>> > > Mega Electronics:  http://www.megaelect.demon.co.uk/
>> > > Number One Systems:  http://www.numberone.com/
>> > > Pulsonix:   http://www.pulsonix.com/
>> > >
>> > > Leon
>> > > --
>> > > Leon Heller, G1HSM
>> > > leon_heller@...
>> > > http://www.geocities.com/leon_heller
>> > >
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