Project: Photographic methods of making PCBs

MCU88

Joined Mar 12, 2015
359
Arh yes graphic arts (the old way) -- is very interesting. It used to be an real skill making something like an poster on an light bench using red ruby, red tape and film from an massive camera. These days any idiot with a camera, Photoshop and QuarkXpress (or Adobe InDesign) -- can do it.

I now use the iron on method with the transfer laser printer paper to make my PCBs. It works.
 

Thread Starter

Lestraveled

Joined May 19, 2014
1,946
great work, but seems all these are 1 layers pcb, how about the 2 layers pcb ?
Two layer boards are done the same way except:
1. You apply dry film resist to both sides at the same time with a laminator, or one side at a time with an iron.

2. You have to align the top and bottom artwork in a way that the sensitized PCB stock will fit between them. I start with a 1 inch wide strip of scrap PCB stock. I scotch tape one artwork to one side and the other artwork to the other side, with the artwork aligned, of course. The strip of scrap PCB holds the artworks in alignment and creates a space for the sensitized PCB stock to fit in between. A piece of tape holds the sensitized PCB stationary between the artworks. Expose one side at a time.
 

MrAl

Joined Jun 17, 2014
7,118
Hello there,

Some good information here, especially by Les.

I just have a couple questions.

1. Can you recommend a red safe light for working with positive presensitized PC boards?
2. Did you ever try a small 5mm red LED, positioned perhaps far from the work area? It only needs to be 'on' for about 60 seconds while the board is taken out of the package and the artwork positioned. Because the alignment can be easy to see (rectangular board and artwork) it should not take more than about 30 seconds to line up before the exposure lamp it turned on.
3. How long is the exposure for a regular 60 watt bulb 2 feet from the board for example, or some way to determine the exposure without ruining boards?
 

Thread Starter

Lestraveled

Joined May 19, 2014
1,946
MrAl
1. Safe light for Positive PCBs - Not red, a yellow bug light works very well.
2. see answer #1
3. A 60 watt light bulb has very little UV output so I would not recommend you use one. Both the positive and negative resist respond to UV light. I suggest a 3 or 5 watt 365 nm UV led. You can try a UV grow lamp, but they are pretty weak. The sun works good but results vary based on the time of day.
4. You have to test to get the correct exposure time no matter which source you use. So, buy extra board for that purpose. Do it right and you will only have to do it once.
 

MrAl

Joined Jun 17, 2014
7,118
MrAl
1. Safe light for Positive PCBs - Not red, a yellow bug light works very well.
2. see answer #1
3. A 60 watt light bulb has very little UV output so I would not recommend you use one. Both the positive and negative resist respond to UV light. I suggest a 3 or 5 watt 365 nm UV led. You can try a UV grow lamp, but they are pretty weak. The sun works good but results vary based on the time of day.
4. You have to test to get the correct exposure time no matter which source you use. So, buy extra board for that purpose. Do it right and you will only have to do it once.
Hi Les,

A yellow bug light, is that what you used? Where can i get one?
So red is no good then at all, even if far from the work area? I dont need much light to work for the 30 seconds.
i have read about the 'curly' light bulbs working with positive resist. Any ideas about that? These are the kind that look like a bulb but have a curly fluorescent tube. Supposedly they emit UV light too.
Isnt that UV light dangerous to your eyes?
For a 3 watt UV LED how far from the board?
 

Thread Starter

Lestraveled

Joined May 19, 2014
1,946
- A yellow bug lamp can be purchased at any hardware or department store.
- I can't say red was no good, yellow is better. I use three, 40 watt bug lights. My work area is well illuminated. You don't have to be in near darkness.
- I have not tried the "curly" UV lights. They should do a better than incandescents.
- Read Posts # 4, 5 and some of 7 in this thread. There are advantages to using an LED.
- UVA (365nm) is the same UV wavelength used in tanning booths. Just be cautious, don't stare directly at it.
- 10 - 12 inches.
 

MrAl

Joined Jun 17, 2014
7,118
Hello again,

Hey thanks Les.
The curly bulbs i was talking about are the new standard for lighting, replacing the old incandescent bulbs. They are widely available so i thought it would be a good thing to try. Since they are fluorescent not incandescent, they emit some UV light although i cant say how much without looking it up.

When i worked in the industry we sent out for any boards that had to be made. Now that i am retired i have to make my own boards if i am to make anything of any complexity. I dont like having to pay 50 bucks for 2 small boards either and wait a month to get them. I saw the photo method as being the least complicated with at least some hope of coming out with a decent board, even if it means touching up a little before the etch. I tried the 'iron on' method but that's too tricky. Point to point wiring is ok for small stuff, but even a decent digital thermometer requires a couple chips and some other stuff which gets hairy to wire up, and then i cant make any for friends either.
Looks like initial cost is a little steep though, but i might try it anyway.
 

DerStrom8

Joined Feb 20, 2011
2,390
I'm sure there are several companies specializing in PCB manufacture where you could just send them your design
Of course there is. I'm pretty sure everyone here knows that. The point of this thread is to eliminate the need for external board houses, and to do the entire process yourself. It's far cheaper.

Altium is a good tool for designing them too!
It also costs $12,000 for a single seat. :rolleyes:
 

MrAl

Joined Jun 17, 2014
7,118
Hi Matt,

Yeah, he he. Have you ever tried the positive photo resist method? Was wondering what other people's experiences might be. I probably only want to make one board every 6 months so i dont want to get into anything too deep financially or too much complexity. Already have laser printer, gave up on ink jets long time ago due to their strong tendency to dry up quickly.
 

jpanhalt

Joined Jan 18, 2008
8,717
I have been using the positive photoresist method since the mid-90's. The brand of pre-sensitized boards I use is Injectoral from DigiKey. For the absolute very best images, I used an HP InkJet and transparencies from Pictorico that had a microcrystalline coating. In fact, they are used by artists for inkjet work. Had the same problem with InkJet cartridges drying up and the Pictorico transparencies became hard to get. So, I changed,

I currently still use the Injectoral boards (http://www.digikey.com/product-detail/en/PC56P/PC56P-ND/354356); although, it appears DigiKey may be discontinuing them. I believe Injectoral is/was a very small operation. Almost all of the pre-sensitized positive photoresist boards have the same chemistry with possibly some slight differences in the color added and concentration of photosensitizer. They can all be exposed with the same wavelength of light, which is a function of the photosensitizer. Ordinary bright fluorescent lights will work, as the required range is approximately 395 to 405 nm. I use a set of three bulbs.

The biggest change I have made is in the transparency. I use an HP4101 laserjet printer on high quality transparencies. Then, I wipe over the entire transparency with a black dry-erase marker. After that dries, I wipe with a soft paper towel, like Kleenex to remove all of the marker from clear areas. The black pigment gets stuck in the small spaces between the toner particles and gives a very dense image that is almost equivalent to the inkjet image in density and sharpness. I only use one layer of transparency with the toner side pressed against the photosensitive layer of the board. I cover with a piece of single-strength glass, but others just use a drop or two of water. Lestraveled and I compared methods awhile back and discovered something very important. NOT ALL LASER PRINTERS WILL WORK WITH THE DRY-ERASE METHOD. HP uses a different toner and fusing method/temperature than Brother. I happen to also have a Brother HL-2270DW printer. It is a wonderful printer, but under a microscope, the toner particles appear like ink splotches rather than the fine particles one sees with the HP printer mentioned above. The brother toner is too easily removed from the transparency. On the bright side, the Brother transparencies are or can be made more dense than the transparencies made with the HP. I think they would work fine as made for the photoresist method.

I have uploaded an image of a board I made last year using the HP printer and dry-erase marker method.
DSCN1376.jpg

John
 

DerStrom8

Joined Feb 20, 2011
2,390
Hi Matt,

Yeah, he he. Have you ever tried the positive photo resist method? Was wondering what other people's experiences might be. I probably only want to make one board every 6 months so i dont want to get into anything too deep financially or too much complexity. Already have laser printer, gave up on ink jets long time ago due to their strong tendency to dry up quickly.
I've never tried the photoresist method. To be honest, I've never tried making homebrew boards, though it's something I've been preparing to begin for some time now. Still need a laser printer, but I have a source or ferric chloride and boards.
 

jpanhalt

Joined Jan 18, 2008
8,717
If you have an inkjet, that is perfect for the photo method, but completely useless for the toner transfer method for obvious reasons. The coating on the best transparencies that I mentioned is ceramic. The sheets look clear, but a little duller on the coated side.

John
 

DerStrom8

Joined Feb 20, 2011
2,390
I have decided to stay away from the photo method because it requires extra steps and extra materials that up the cost. I'll wait until I get a laser printer and I'll just use the toner transfer method.
 

jpanhalt

Joined Jan 18, 2008
8,717
upload_2015-9-7_0-0-42.png


I may have left some steps out of the toner transfer method, like all the cleaning and preparation of the PCB that must be done so the toner sticks. Ordering presensitized PCB material online probably offsets all that effort.

John
 

Dr.killjoy

Joined Apr 28, 2013
1,196
I have decided to stay away from the photo method because it requires extra steps and extra materials that up the cost. I'll wait until I get a laser printer and I'll just use the toner transfer method.
Try a flea market or even you job cause I got one when my job upgraded and threw out the older models... I want to try using a printable clear sheets in another thread I posted cause it looks alot easier and less work...
 

nerdegutta

Joined Dec 15, 2009
2,676
I have decided to stay away from the photo method because it requires extra steps and extra materials that up the cost. I'll wait until I get a laser printer and I'll just use the toner transfer method.
When I make a series of PCBs, I use a homemade UV box. Most of the parts I had lying around, but the LEDs were bought on eBay. With free shipping.

Double-sided PCB UV box.

For one-off I use the toner transfer.
 
Top