PCB Manufacture

[Coyoteboy]

I know its not 'axe specific but since I was considering using a pic for this, I thought I'd ask peoples opinions...

I'm looking at making a UV exposure box, i have an old scanner and I was planning to make a scanning UV LED head that cruises slowly across the artwork - had a lovely 15mm/min min cruise rate from it with the 08M at 4MHz, and cranked it back at ~1000mm/min while on 8MHz. All was good until I blew the 'axe somehow (cant figure out why, but thats not important anymore). But the postage costs thread I posted got me thinking...

I can buy 4 9w UV bulbs and wire them up to a standard ballast from a fluorescent tube setup (£6 sent from china), or I can purchase 100 UV LEDs and have them sent for the same cost, but then buy the new picaxe etc.

Who would do what? Reasons for and against each are welcomed to help me justify the extra cost

 

[BeanieBots]

Are the LEDs the right wavelength?
Beam angle?

I'd go with tubes because you know (assuming you get the correct "UV" type) that they will do the job. LEDs might give "hot" spots and/or be of wrong intensity/wavelength.

The choice has to be yours.

 

[Coyoteboy]

I'm told that the wavelength is not as important as people think, and that almost any UV source will work, but with varying exposure times. The problem with hotspots I was going to target with ~100 3mm LEDs in close proximity, beam patterns overlapping slightly but its not ideal of course. Lamps will also produce hotspots, but I hear its limited.

Another method I've seen is to use direct inkjet printing and then bake the ink - sounds interesting.

 

[picaxester]

Check this out

 

[Coyoteboy]

Thats impressive! The size of those SMT traces!

I've decided to go with the UV tubes, easier for me to set up in the end.

 

[Mycroft2152]

Direct inkjet printing of pcbs CAN be done. It is a relatively new technique about a year old and has only seen llimited success There is a lot or work, trial and error to get it to work correctly.

Another method is "Toner Transfer". .

TT is probably the least expensive pcb process to start. TT can be done with a copier and a household iron. But it takes a bit of fine tuning to get it right. One hint, make the traces and pads oversized. You'll have fewer problems later.

There is a Yahoo Group - Homebrew PCBs that has excellent info on the different methods.

http://tech.groups.yahoo.com/group/Homebrew_PCBs/

Note: yopu will have to have a Yahoo ID to access the messges and files.

Mycroft2152

 

[Coyoteboy]

I tried TT methods and found it a bloody nightmare, I used the peel n whatsit blue paper which works 50-75% of the time but I have to have access to either a good quality photocopier or a laser printer- neither of which I have at home which is when i need it. If I worked in an office more regularly I might stick with it, but even so it wastes large amounts of the paper as you have to align the printout with whats left of your blue stuff, and make damn sure you dont get fingerprints on the paper between trips to work. Oh and you have to stop everyones access to the printer while you pop your blue stuff thru. I havent tried on "normal" paper but I cant see it being easier than UV/acetate with an inkjet?

 

[Mycroft2152]

Any of the pcb techniques has a learning curve, plan on screwing up a few boards. Yes even the photo methods.

Which process you use depends on the equipment you have available and how deep your wallet is.

TT is being done on many types of paper, from photo paper to slick magazine pages. The 'blue stuff' tends to be very expensive.

According the the 'experts' on Homebrew PCBs, yellow inkjet ink on vellum works much better than black on acetate sheets. The yellow ink aborbs UV better than the black ink, and the vellum prevents pinholes. Don't forget to run an exposure test before running your first board. Pre-sensitized boards can be expensive.

Good Luck

Mycroft2152

 

[BrendanP]

I've made a lot of boards with the blue film and a el cheapo HP 1010 laser printer and have had no problems. The boards came out fine even the first ones I did.

Make sure the blank board is pefectly clean.
Scrub it with NEW steel wool and detergent under running water before you use it.
Make sure its nice and dry.
Make sure the iron is hot enough when you iron the film on.
Put a sheet of blank paper on top of the blue film before you run the iron over it.
Press down on the iron very hard as you move the iron around.
Wear some cheap rubber throw away gloves if your getting oil off you hands on the job.

 

[Coyoteboy]

One tip I have found for the blue film - dont forget to turn off the steam feature of your iron. That really doesn't help