|
persiangulf
Guest
|
 |
« Reply #55 on: April 19, 2008, 04:12:52 04:12 » |
|
Using laminators will give people mixed results and most laminators are not designed to feed a typical PCB due to thickness, this results in your lamintor loosing its pressing pressure overtime in the centre depending on how you insert your board. Also, the temperature is low on most laminators, but since you guys are into electronics, its easy to mod a laminator to operate at higher temperatures, but beware you do not melt the housing.
Laminators are not reliable in the sense that you might have to buy a few to find the right one, and even then, you risk damaging it by continuously feeding over-thick material through.
Using the Iron is the riskiest and most unreliable method regardless of which paper and how you use it, unless your end board is small and single sided.
The most common problems with toner transfer is the printer. Today, most new printers are designed to deposit as little as possible toner on paper, and most toners today are designed to provide the same amount of colour saturation with far less toner present on paper, meaning, its good if you want more pages per cartridge, but bad news if you want more toner on each page for transfer purposes. I have not come across any printer allowing you to choose how much toner you want used, although all have the typical economy, normal and best modes. The problem is, the best modes today give out as much toner as the economy mode 10 years ago.
This is due to better toners being produced and newer laser technology allowing the same print with less toner. You guys also have to note, there are different types of toners and some melt at different temperatures, although not wide on a spectrum, but enough to make some toner transfers successful whilst others fail.
I remember once, the office printer/copier was ordered by the boss to have its cartridges refilled with non-brand toner rather than replacing the cartridge with the same brand toner to save money, which resulted in disaster. The refill toner was melting far too easy and resulted in the pages full of smudges (i say smudge, but its different to that of inkjet...... imagine a stamp being pressed onto a piece of paper extra hard, everything gets bolder) where one letter was joined to the next, a's looked like fat b's etc. Anyway, the printer/copier was also ruined and needed a service.
Also, what happens, is some people find, this paper works for them, or that laminator works for them, then they tell others, forgetting that that particular laminator, and paper only works with a sufficient amount of toner present on the paper to begin with.
Laminator/Iron Method:
For newer models of laser printers, the thinnest possible paper should be used that has a glossy feel, however, you have to watch out you don't use too a thin of a paper otherwise it will jam in your printer as it tears during feed in. For single sided, cut out the circuit from the paper using scissor or others, and place on the ccb (copper clad board/pcb) and feed through your laminator. You can use normal photo/glossy paper, but will not work on most 2005> printers.
If your laminator has a habit to disposition your paper circuit during feed in, then simply use a small strip of masking tape attached on two opposite sides of the board fixing the paper circuit on the ccb. Some laminators require you to feed it in a number of times before the toner sticks to the board, some less and some more, but I have not come across any that does it in 1 or 2 goes. Once you feel the toner has stuck to the ccb, put it in warm or normal temp. water until the paper used tears away without effort. This is where many people go wrong, they try to scrub off, or use slight force to take away the paper which results in cut tracks or other errors.
Anyway, if you leave it long enough, it should come off easier than a wet tissue, slowly start from areas with less tracks/pads then when entering areas of detail, try to rub your finger across the same way of the majority of the tracks, in other words, rub along the detail, if you have tracks going from right to left, rub from right to left.
If done right you will have a nice toner transfer. Back to the feed in step, to ensure you're laminators springs and pressure quality remains constant over continuous use, feed in the board+paper orientated to allow the widest entry, this may result in you having to feed in a few more times, but allows your laminator to work for such usage longer. On the other hand, if you feed in orientated so the width is the least, you may have a better transfer but you also risk ruining the laminator quicker. This also depends on your laminator, and how it applies pressure,whether by springs etc.
Some of you may find that your printer uses toner that is hard to melt or that there is not enough toner even at best quality, this will normally result in the laminator only sticking the paper circuit on to the ccb, but not transfering the toner, and it will peel off without leaving any trace of toners. 1. this could be due to an improper cleaned ccb, but normally, if it was not cleaned properly, then there should be atleast some sign of transfer. If there is no sign of transfer, then run the thing through the laminator a few times again until it sticks again... whilst its still warm/hot from the laminator, grab the iron and finish it off there.
Iron:
If your laminator does not do the job, it still is a good tool to fix on the paper circuit on to the ccb before ironing. If you are ironing, you have 2 options, either have it on a very hot setting, but be very brief and confident that you are applying even pressure. The second option is to use a medium heat setting, and then taking your time applying pressure.
Make sure the bottom of your iron is cleaning so the paper circuit does not come off or move off the ccb whilst your moving the iron. Don't use steam or any steaming that your iron provides, it does not make much difference and may also ruin the process. One thing you can do, which works well if done right, is straight/immediately after you lift the iron the final time confident the toner is stuck and transferred (I am saying Transferred, but the truth is, the toner will always be sandwiched stuck on both the ccb, and paper, unless the paper you use is special like PnP) then add a few ice cube on the back of the paper.. if done right, the toner due to sudden change in temp. will repel from the cold side (paper side) and stick to the ccb. Then proceed to drop the whole thing in warm - normal temp. water. Boiling or Hot water is not recommended, UNLESS you have bad bond or a different type of toner that works well repelling from paper under such conditions.
Etching:
The etching process is simple, dependent on the etching solution and environment, it shouldn't take more than 5-40 minutes. I recommend everyone to buy a etching bath, it makes the whole process faster, and also allows you to roughly estimate when the etching is done. For ferric chloride solution, add 5-10 seconds on top after you etch each board as its corrosiveness degrades according to usage. Add 20 seconds or more if you are etching larger boards. These times will vary dependent on the ratio of the solution and water as well as how much solution there is for the size of board you use.
UV Exposure Method
The BEST way, and beleive me, I have tried all the previous methods, is to use photosensitve copper clad boards. If you are thinking of spraying your own boards for them to become photosensitive, its not really worth it, unless you have switched to using photosensitive boards and you just want to convert some of your old normal copper clad boards. Buy photosensitive copper clad boards to begin with, and the price difference is not much these days, probably around 0.5 x more than the normal copper clad boards.
The best light source is UV-B tan tubes. You can buy a facial tanning machine for around $50 on ebay that has 4x15watt tubes that is housed with a timer. All you have to do is tilt it so it shines upwards, place a clear piece of glass or open up an empty scanner and take off of the top glass/clear plastic unit with the lid attached an place it on the tan unit. If you want, you can make a custom case using a scanner, and disassemble the tanning unit and place the tubes, starters, ballast and circuitry inside, but personally, I wouldn't bother, because you never know when the winter blues might hit you, which is when the tanning machine will become usefull ;-) You can use UV-A or UV-C but is not as fast as the UV-B tubes.
Use a frosted tracing paper to print on and place over the photosensitve copper clad board, and leave under then the uvb light. You need to use a frosted tracing paper so the uv rays are spread evenly, otherwise you will get areas of overexposure and areas of underexposure. You will also loose the ability to do fine tracks if you don't use froster tracing paper. If you can't get frosted tracing paper, DON'T WORRY, all you need to do, is just frost the glass/clear plastic which you will be placing the boards on and use acetate printing paper instead. There is not much difference on whether the clear plastic/glass panel is frosted or whether you use frosted paper instead.
All you need is something to diffuse the light evenly, and if you find other methods then thats fine too. The only thing is, there shouldn't be too much distance between the diffuser and the printed tracks. The distance between the UVB tubes and the board should be around 5-7 cm. The further away, the longer it takes, the closer, the more chance of uneven exposure. With a diffusor, 7 cm is the optimum for 4x15w spaced the same way as the facial tanning machines.
Anyway, when I started using these 4x15w uv-b tanning light i used to leave my pccb's for around 5-7 minutes, thinking I needed to see atleast abit of the tracks on the photosensitive side before I dip them into the developing solution. Everytime I dipped the board in the developing solution, the circuit got dark quickly on the board and then melted away in a matter of 10 seconds. This was odd, I thought the solution was too concentrated etc. I blamed everything except my exposure time. I then realized 5-7 minutes exposure is toooo much, I now expose my boards for 30 seconds under the uv light, and then dip them into the developer for 20 seconds, then give them a rinse and then off to the etchant.
It is easy to do double sided too, there are numerous way, I will tell you the way I think is the most reliable:
Double Sided:
1. Print-to-file both sides of your circuit board, use photoshop or another photoediting program and align both of your circuits end to end, but with one of the mirrored and the other flipped in a way so when you print, you can simply fold the paper and the circuits will align with each when you look through the paper under light. The gap between the fold should not be much, however, draw a center line in the photo editing suite you are using so you know where to fold.
Once you have printed on paper your circuit design, before folding, trim off excess paper, leaving only 0.5cm / 5mm gap between the edges of the circuit and the trim. Now fold precisely where your center line was, further sharped the fold by going over it with a ruler or something hard, watch out the design does not come off alignment when doing this, keep checking under light and use masking tape etc. if needed to help you.
Remove anything you may have used such as masking tap and place your pccp/ccp in between the paper so its like a pita sandwich. Use masking tape to hold the paper onto the board on both sides so it does not move when you flip it over under the UV light or when passing through the laminator. In the case of UV you should use a tracing paper because acetate is hard to fold etc.
Once you paper is secured to the board, drill 2 holes precisely through to the mounting pads (you need to add some during the design, or add some non-usable pads so you can check your alignment, make sure the pads you add are opposite of each other on both axis's such as ona hypotenuse of a triangle). Now check carefully to see if he holes align with the paper marks. If so, then proceed with lamination/ironing/uv exposure.
In my opinion, the best method for circuit development is the photosensitive method. I have never ever been able to get such detail, clarity and track width as I do with the photosensitive method. It is by far the best method for 3 reasons, 1. It is consistent, you can rely on getting the exact same results each time 2. You can achieve far more detail, surface mount, tqfp, no problem. 3. it is quick
You may have tried it and not been able to get good results, but i strongly suggest to use my method, and also ensure you buy ready photosensitive copper clad boards, and also ensure you use UVB with a diffusor. tw8
|
