Tube Amps / Music Electronics
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|5/27/2000 2:45 PM|
Having spent a few years modifying existing effects, and making occasional stripboard circuits, I'd like to have a go at making some PCBs. What methods would anyone recommend for a beginner?
I like the idea of press'n'peel, but it looks quite costly if I do quite a few. I've got access to a light box for doing exposures, but having looked at the systems available I've really got to commit to a system before I buy any chemicals, etc.
Also, is it worth gearing up to do double sided boards from the start. It does seem to make bigger circuits a lot easier to route.
Thanks for your advice
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|5/27/2000 3:04 PM|
Everyone has their own idea what is 'easy', what is 'cheap'. There aren't many (if any) guitar fx boards that need double sides. It's a lot easier having a few links rather than having to match up the sides & try to do plated thru holes at home (expensive and tedious). Our kind of ckts dont get more complex than the Boscorelli ones in "The Stompbox Cookbook" and his routed OK on one side.
Having said that, the gear I produce commercially is on double sided boards, because it costs very little more and you can put in ground planes for noise control.
|5/27/2000 3:09 PM|
I would think that imaging the circuit pattern is the most difficult part. If double sided, how would connect the circuit through the board? I guess you could insert an eyelet through the copper trace but they would have to be lined up perfectly on both sides. Then, solder the trace to the eyelet when soldering in the component. Never done this, just guessing here. In PCB production, the hole drilled through the board is made conductive and copper plated. Then, the image is etched into the copper surface. If you have a few one offs I could help you and make the hole conductive and copper plate, too. Can't help in the imaging dept though. But I do have access to etching chemistries. If you have a few to do maybe I can help. Can't do production volume. E-mail me if you want.
|6/3/2000 1:03 PM|
|Daniel R. Haney
Jim Martin wrote:
> I would think that imaging the circuit pattern
> is the most difficult part. If double sided,
> how would connect the circuit through the board?
Sorry for the late reply.
Two-layer boards are an ambitious undertaking
You have faith that the layers line up because to
put registration marks on the top and bottom side
resist patterns and lined them up as best you could.
As you said, commercially-bought eyelets are pressed
into pads to connect the layers.
Commercial PCB fabricators plate the copper through
the holes. This anchors a solder pad to the board
and permits reworking the board with minimal damage.
Two-sided boards with plate-through holes don't sound any better than single-sided ones, but
they are a lot more rugged.
|6/3/2000 7:53 PM|
reworking double-sided boards can be a real challenge. the plated-thru holes are very difficult to clear on a multi-pin component and you do more damage with the excess heat from multiple tries than you would on a single-sided board. i have to say from personal experience, if i had to change a transistor on a double-sided commercially-made board i would ask my assistant to pull the piece out with a needle-nose while i heated all three leads at once, and then clear the holes later with a sucker. on the other hand, i could work alone on a single-sided board repair.
|6/3/2000 11:20 PM|
||Pulling parts on double sided boards|
The only real trick to pulling parts from double sided board is to pull gently from the part side while heating the solder side with a hot gas setup.
When I was desperate at odd times in the past, I have managed to use a propane torch *very, very, very, very* gently to melt the solder. It's a clumsy tool for this, and will actually burn the glass-epoxy if you don't have a good touch with it. The gasses are just too hot, maybe 1500F. A hot air gun with some kind of speed control to keep from scorching the whole board works pretty well. If the air temp is about 600F, it's pretty forgiving.
A propane torch is GREAT for removing parts from junker PCB's though, where you don't mind losing the board itself. I've removed semiconductor memory chips this way, and got about an 85% yield after the abuse.
|6/4/2000 9:20 AM|
i suppose that would make it possible for one person to do the work, if the hot air/gas source was fixed to the bench and you have one hand to pull parts and one to hold the board. i bet it won't be too long before there is a shortage of so many leaded parts that we'll all need a bunch of specialty gear to assemble and rework surface mount stuff.
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