Each method has it's plusses and minuses listed below each section. Compare these to the last method (#6) which is our "Direct Etch" technique. It has as the greatest advantages with the least detractors to give you the best "bang-for-the-buck" with regards to speed, efficiency and cost.
Method #1... BY HAND
This is the most basic "quick" method of making simple PCB's using a "Sharpie" indellible ink pen or rub-down tapesand donuts.
WOW! Pretty scary looking, huh?
This was Ok I guess for hobbyist boards back in the '50s but there's no excuse for this in today's electronics.
BY HAND relied on using a waterproof pen like a Sharpie®. There used to be pre-printed dry-transfer images specifically marketed for making PCB's (adhesive tapes and donut pads) from "Datek" as well as others but as of late, they don't seem to be available any longer. Even with those you had to remember you're drawing it backwards being the bottom of a thru-hole board.
Both the "pen" and "tape" techniques are successful at stopping the etchant from attacking the copper beneath the images (for the most part) however, the real big concern is the level of quality. Hand drawn images with a water-proof pen are quite literally quick 'n dirty whereas the dry-transfer tapes and donut pads are clean but time consuming.
Probably the most difficult part of this very simple technique is that you draw the circuit in reverse. Instead of pin1 of an IC being in the lower left of the grid of pins when viewing it from the top of the component, because you are drawing the traces from the back ofthe board, pin1 is drawn from the top-right! It can be very confusing and is prone to lots of simple mistakes that are not easily correctable.
Sure you could create the pattern on a sheet of acetate to use as a master image but you'd then be doing the "Photographic" method... and that is an excellend "lead in" to the next METHOD.
- Fast technique
- Very inexpensive
- No negatives
- No developing chemicals
- No support equipment
- No duplication.. "1-shot" deal
- Poor reliability (with the pen)
- Easy to make a mistake
- No trace-width control
- No "fine pitch" traces
Method #2... PHOTOGRAPHIC
This has been the most common method for the serious "midnight engineer" as well as R&D labs of larger corporations who do their own designs through production.
This process requires a lot of support equipment. Darkroom, hot roll laminator to apply dry film to raw copper laminate (or buy expensive pre-sensitized PCB blanks) UV exposure box and meter, (or use the hit 'n miss approach using varying UV from the sun!) developing trays and chemicals. Then, make a film negative of your design with a photo-plotter image setter (expensive unit so most people find someone to perform this service normally found in a state other than yours so you have long mailing times.
As you can see, this can be a pretty involved procedure and this technique takes up quite a bit of time and dedicated space. It's not the fastest and it's not the cheapest method, however, results can be very good once you know what you're doing and it does allow for limited mass production capabilities.
- Excellent reproduction
- Excellent resolution
- Excellent repeatability
- Quality appearance
- Fine-line capability
- Lots of support gear
- Must have a darkroom
- Requires film negatives
- Time consuming
Method #3... SILK SCREENING
Definently not in the definition of "quick-prototyping"! This process is only practical for mass production of a large number of boards.
You have the same basic requirements as that of the photographic process described above with the only differences being instead of applying an emulsion to each and every circuit board, you only expose and develop a screen which has been coated with a photo-sensitive material and you need a transparent "positive" image.
This typical "kit" is shown here except you'd only be using one color of ink. The way it works is quite simple. The taught screen in the frame is coated with an emulsion under bug-light conditions. When dry, the "positive" artwork is laid over the screen with pressure and then exposed with a UV source. After exposure the screen is subjected to a high pressure water bath. Those areas of the coated screen that did NOT get UV (eg. the circuit image) stays soft which will wash out with the subsequent water bath. This means the screen has permanently "open" webbing to allow ink to pass through to the copper surface of the board placed underneath. It requires practice to obtain the skill to do reliably and can be very messy. Down the road if more boards are to be made, you'd start all over again since screens are expensive so they are are used for the next project down the line, otherwise, having a lot of different screen frames lying around can become an expensive proposion.
It is a kick to play with if you've never done it before and a real eye-opener into the myriad of applications that silk screening can be used for, but like the "photographic" of making PCB's silkscreening can be quite involved, time consuming and expensive.
- Fastest imaging method
- Fair to good imaging quality
- No developing chemistry
- Can be very messy
- Time consuming setup
- Bug-light "darkroom" required
- Film positive required
- No "fine-line" capability
Method #4... SEND OUT
Not much that can be said here for this option. It is however, a great way to have boards made for you if you have lots of money that's burning a hole in your pocket!
If you're not versed in Gerber file format... get familiar with it! All board houses require this standard format. Next, pay the man a lot of money and wait a week or two. This sounds great doesn't it? Eventually, you'll get back a half-dozen boards, (somebody please tell us why you get 6 prototype boards when you only need one... maybe to help you justify in your own mind why you spent so much money perhaps?)
They do a really great job, but you are paying through the nose for this great work complete with all the amenities... most offer fine-line capabiltiy, solder mask, plated-thru holes and a silk-screen layer on top. (Some board houses will not even do traces finer than .010"!)
- High quality boards
- Excellent resolution
- Thru-hole capability
- Able to do more than 2 layers
- Fine-line capability
- Most expensive method by a long shot!
- Long wait times for normal "turn-time"
- Very expensive next-day express services
- Gerber file generation required
- If you make an error, you've double your cost!
Method #5... MILLING
One of the newer techniques is to simply create outlines around where the trace is to be and ...voila! The big plus is that no chemicals are involved at all.
These milling work with your PC on a standard "X-Y-Z" geometry table much like that of the venerable "pen plotter" except instead of a pen there is a high speed drill holding a router bit for making trace outlines and a drill bit for component holes. The machine is set to just barely cut below the thickness of the copper.
All of this comes at quite a cost. LPKF is probably the worlds leader in this type of high-end type of prototype/1-up PCB fabricator with prices upwards of $50,000, however there are other companies that start at much lower prices around the $9,000 range. Is this worth it? We feel this is questionable at best when you compare cost for actual performance and whether or not simple chemicals can be used in your work environment. For some who absolutely can't have any chemicals this technique becomes quite attractive but for most, it's too expensive for what it produces. Any way you look at it, this type of machine is going to be expensive.
One more problem we just recently heard from engineers who have this type of system in their office is the problem of the slightest warp on a board! The router is cutting just a few thousandths deep to remove the thin copper laminate so any micro warp causes missed traces all together! They have told us of some real horror stories of this otherwise great piece of expensive engineering.
- Very good routing & drilling all in one shot
- No photography, negatives or chemicals
- No long wait times (except if your office has mulitple users are waiting in line to use it)
- No Undercutting of traces
- Extremely expensive! The LPKF 12" table runs about $25,000
- Trace pitch based on how small of a router bit you can use
- Mini-mass production not such a great idea
- Slow process
- Single & double-sided boards only
- The slightest bow on the board means missed routing! The most frustrating problem with routers!.
Method #6... "DIRECT ETCH" (Our process)
Toner "powder" used in all laser printers and photostatic copiers contains 55% pulverized plastic (along with 8 other basic ingredients). A printed toner image can be made sticky with heat and pressure to make it stick (fuse) to a copper surface (or any other material for "Chemical Milling". Click your "BACK" button to return here).
Toner is also waterproof by its very nature making it an ideal "etch resist" when the circuit board is submerged into conventional etchant like Ferric Chloride, Amonioum or Sodium Persulphates.
With the current relatively high resolution printers (eg. 1,200 dpi) PCB traces can be made so fine, we can now design and print images that enter the world of "fine-line" capability. To make a "system" out of this basic technique, several items are put together to accomplish this straight forward task.
- Print the image to a water-release paper
- Transfer the image to the copper surface with the applicator device
- Remove the paper by wetting the board
- Seal the toner image with a special green film to prevent pitting
- Etch the board to remove all exposed copper
- Remove the toner circuit image with acetone... done!
You have now seen all 6 basic "techniques" for making PCB's. What makes the "DirectEtch" method standout from the rest is summed up here:
- Very LOW cost system
- Make single & double-sided boards
- For both Thru-hole and SMT components
- Fabricate single-sided boards in 8 minutes
- Fine-line capable down to .005" traces
- Silkscreen PCB in pure white
- Great imaging quality equal to your laser printout
- Excellent resolution down to .005" trace pitch
- 8 minutes to make an average S/S board
- Fine-line capability to .005"
- Create white silkscreen layer
- Very low material costs
- Telephone tech support in USA
- Must etch the board using conventional etchant
- We can't think of a single other disadvantage!
NOTE: Even though we say "any printer" can be used, there are two exceptions to the rule here.
1) The "BROTHER" printer line can not be used because the unique toner they use in their engines is radically different from "conventional toner" and will not fuse properly to the copper surface).
2) The printer itself (laser or copier) must be a B&W device. Color printers will NOT work because their toner density is way too low to be able to fuse to the copper board.)
We have a page dedicated to "Printers" here if you missed it earlier.