Professional aluminum metallized film manufacturer for over 13 years experience.

printed circut boards - complete process - transparency film

by:Cailong     2019-07-15
printed circut boards - complete process  -  transparency film
Below describes my process of creating a PC board for one-
And prototype use.
It was written for people who have created their own boards in the past and are familiar with the general process.
All my steps may not be optimal for your situation.
I developed this process through trial and error, including technology from various sources.
Please take anything that is useful to you and discard something that is not.
A production note: I am an old school and learn the best from written teaching and pictures, they make up most of this teaching sheet and I have included for some more complex steps
The list below is long, however, you may have some of these items if you are already making your own PC board.
Except for the UV exposure box, most of the rest can be in-line.
You need: I use the Eagle free software version because the board size is fairly moderate and is limited to two sides only.
I am generous with the size of my marks and the distance between them (
Minimum tracking size between 24 mil and 15 mil).
Most of my components are through holes, but I use SMD or combinations occasionally.
I am trying to route the track to any pin header at the bottom of the board.
I don't use the plated holes so I added extra holes to connect the top track to the bottom and at the bottom the Assembly can't be welded on both sides.
These will be filled with fine threads welded in place.
When I finished the layout and wiring, I added a few large holes near the corners of the board as mounting holes and registration indicators for the dual panels.
When you are done, I suggest you print a large copy of the board for your reference when placing components and marking holes.
I use the CAM processor of eag to create a plate image that will be printed on copper paper and printed on the laser transparent film of the welding mask.
I like to create a ground plane at the bottom using a fill polygon and a V plane at the top, so I don't print the Board Image (s)
Use the CAM output of Eagle directly.
I haven't used solder paste templates since I started
Weld several SMD components I use to my motherboard.
To facilitate the creation of CAM images, I created a custom template for single and double sided CAM outputs that contain the output files I need.
I always add a plate shape to the copper sheet, but don't add a plate shape to the mask.
When working on jobs, I usually put the Gerber files in the project folder so that they can be accessed later when needed.
Creating output using Eagle's CAM processor creates several obstacles to the creation of copper and welding masks.
The first step is to convert the Gerber file to some sort of image file, and then I can edit and print.
I used a utility called Gerber2PDF Gerber2PDF link.
Exe is placed in the Eagle CAM directory.
Then, before running Gerber2PDF from the Windows command line, I will transfer the Gerber file that I want to convert from the project directory to the CAM directory.
For syntax for selecting and converting a specific file, see the Gerber2pdf documentation.
I have included the text file I used to run the gerber2pdf process you should download.
Please feel free to edit this file to suit your needs.
Cut the command and paste it into the DOS command line utility to convert Gerbers.
Once I have prepared a separate PDFs for each copper and welding mask I need, I solve the problem of missing holes in the circuit board assembly, vias and registered holes.
I use PhotoShop to import PDFs and edit the copper file to add the desired hole as a small white circle filled.
I use PhotoShop to import PDFs and edit the copper file to add the desired hole as a small white circle filled.
You can use your own graphics conversion and editing software as described below.
Edit the PDFs to add the registration hole mark (see Arrows)
2-on both sidessided boards.
Keep the extra small registration holes to make the registration more accurate, but large enough to be seen when you print the copper image.
I only add Assembly holes to the top because I will drill holes mainly from this side.
Note that the top copper image must be flipped horizontally (mirror)
At this point, the pads match after etching.
At this point, you can also add print text.
Make sure that any text you add is displayed on the copper at the top and bottom so that they can be transferred correctly to your board (
See example above).
Copy and paste each copper and mask image into a blank full page master page (
Same resolution as PDFs)
This will be printed on your laser printer.
You may also want to add the board identification text to the master page.
Placing multiple copies of the copper image on the main paper saves paper and allows errors during toner transfer.
Do the same for adding at least 2 welding shield files for each shield, and they will be combined later.
Using toner heat transfer, the printed main copper sheet image will be transmitted to the prepared pcb.
I use from Staples (633215)
For the transfer process.
Reliable, low cost, clearly visible (
Not like a magazine page).
It accepts laser toner, with almost no errors, quickly transfers toner to copper and can be released cleanly by simply soaking it in warm water for a few minutes.
If you want to generate a welding mask, print at least two copies of each mask on the laser printer transparent film (C-Line no60837).
Please print a copy of the image on normal paper before printing it on paper or transparent film.
This copy will be used for plate size and double sided copper alignment.
It is a good idea to check the correct distance between the pads of SMD and other components (See above).
Do this for both copper and mask images.
I made more than one mistake in copying and pasting, and after etching, masking, and drilling the PCB, I was unable to fill the copper plate on the finished Board (
Single or double sided)
Cut into a rough shape (
~ Full arround half inch)
Use the image in the print output of plain paper as a guide (
I use the Dremel tool with cuttingoff wheel).
The edges are smooth, making them flat, and the corners are round.
I then archive the top and bottom edges at a 45 degree angle to eliminate any burrs or sharpness (
Check with your finger after filing).
The next step is to clean the circuit board to remove any oil or grease.
Just wash the detergent and warm water.
Finally, in order to remove oxidation and create a surface that can accept transfer and is easy to weld, I sprinkle it on copper with a little "bar administrator friend" compound and gently scrub it with a damp sponge, then rinse clean before drying with a paper towel.
If the plate is 2-
Sided, images need to be registered accurately.
I find that the best way for me is to gently stick a copy of the plain paper of the bottom copper image to one side of the board (
Paradoxically, this will be the top)
And carefully drill through 70 drills to register the center of vias.
The bit with the bit pair works well.
The process is quite simple for a single panel.
Just cut off a copper image from a smooth sheet of paper, then gently stick it next to the board image with painter tape (blue tape).
I then put the board on a piece of plywood covered with two layers of paper and covered the board with another two layers of paper.
This process is more complex for dual panels.
I first use a straight pin to clear the registered hole on the board.
The next step is to cut a copper top and a bottom image from a smooth sheet and accurately pierce the center of all registered holes with a straight needle.
Next, I cut thin pieces (~ 26 gage)
A small enough flower shop or craft line through a registered hole (
About 3/4 in length).
I first go through the back of a registered hole on the top sheet and then through the board.
At this point, I bend the wire and use a small piece of painter tape to prevent the wire from falling when I flip the board.
Finally pass it through the front of the bottom paper hole so that the image can face copper.
Then, bend each wire and fix the paper and board together.
When all the holes are completed, follow the procedure of the single panel above.
Now the board is ready for the toner transfer.
This video of the transmission process may make the following instructions clearer.
I applied a dry iron at the highest temperature and glued the paper to the cardboard with the iron tip.
Carefully place the tip between the two wires
Side plates and fix both sides so that the paper is not separated from the plate when treated.
The warning board is hot.
On both sides of the board, I cut off the flush wire on one side and then cross the other side through the paper and cardboard before the next step.
Remove any tape before applying an iron with a pressure of about 1 minute on each side, unless the circuit board is large and can completely cover the iron.
This will heat the dip plate and stick it to the toner.
To ensure toner transfer, I remove the paper towel at the top, keep the iron edge at a 45 degree angle to the board, and then apply pressure when moving across the board.
I have done this at least a few times on both sides.
At this point, you should see a slight image of the toner on the back of the paper.
The next step is to soak the cardboard and paper in the water until the paper comes off.
I usually rub the back of the paper gently to remove the clay coating for easy handling, gently peel the paper after a few minutes, and gently brush it underwater with a soft brush or finger, it is possible to ensure that the clay coating of the toilet paper is removed from the copper before etching.
Water cloud-
Microscopic clay particles.
Dry, check and touch
Mark and knife with shark if needed.
If extensive repair is required at this stage, you may want to remove toner and re-apply it before etching (
Be sure to clean the board again).
My etching process is perhaps the most unusual.
It needs a can filled with a tank of 1/2 road, holding water High and heating (at least 1 Hr)until hot.
The next unusual step is to etching the plate in a high quality freezer bag with a zip lock.
Finally, I used a Edinburgh etching based on iron chloride to prepare as follows: get some dry citric acid (
Also know the acid salts that are often used as food preservatives}from an on-line (NUTS. com)
Or local sources.
Dissolve 1/4 cup powder in 3/4 cup of warm water and cool it for standby to prepare citric acid solution.
In order to make etchant add 1/2 cups of this solution to 2 cups of 40% iron chloride solution.
Add acid to chlorine.
It was etched in Edinburgh.
The etching solution is twice as fast as ordinary iron chloride etching and does not self-clog or form sludge.
Warning: Do not use hydrogen peroxide-based etching agents in this way.
It will produce explosive, flammable hydrogen and blow the bag away.
Be sure to use gloves and clothing protection (
Waterproof apron)
Before mixing or using etchant.
It will also stain the cloth and skin!
Open the bag with the circuit board, I usually add water in the bag first to test if there is a leak, and then pour the water out.
Add enough etching agent to etching the circuit, don't overfill, you can add more later, however, it can be messy.
You will find that you will use less etchant compared to other methods, because it will be discarded after use, so etchant is always fresh.
In the absence of overflow, squeeze out as much air as possible from the bag, and then seal it safely so that it is airtight.
Turn off the pot.
Now put the bag in hot water until the board is flooded and flattened.
Check the etching progress at least every 5 minutes until all exposed copper is completely cleared (
Clear bag allowed to check).
There is no need to keep stirring because the Edinburgh etching is not blocked.
When complete (
Copper is not visible)
, Take out the bag, open it carefully, discard etchant in the waste container and do not pour it into the drain!
I use a plastic container with a big mouth and I take it to my community for hazardous waste collection to discard.
Rinse the bag with water, also discard the bag into your waste container and remove the board before dropping it.
Wash the board under running water to clean before removing the protective gear.
As usual, wipe the toner with paper towels stained with acetone or paint.
Once the circuit board is dry, it's time to apply a solder mask.
This is an optional step, but it will help to protect the copper from oxidation, look more professional and improve the placement of SMD elements.
Again, since the description of the process does not convey all the nuances required for success, I have included a video.
Thin film masks are hard to find and very expensive, so I used tubes for UV curing welded masks obtained from various sources on the Internet.
Whether you're using film or paint, you need a UV light source.
I built a UV exposure unit with a roll of purple/UV LED strips.
: To protect your eyesight, it is important to close the UV source in a well-lit box.
There are many directions to build other UV exposure devices on structures.
Com, build a suitable one for you.
I use an electronic timer that can measure the second and activate the relay to turn on and off the DC current of the UV source.
Since the image density printed by the laser printer is not enough, you need to combine two images.
Cut out two copies of each welding mask from the film and align carefully to form a mask on each side.
I stick them permanently together with a small piece of "super glue" and put them in a relative corner away from the printed image.
The next step is the most heuristic and you need to test your exposure settings (
Please see the instructions below)
And some experiments on your paint application.
Test your UV exposure device
I don't know what kind of UV level your device will output or your paint thickness, there are too many variables.
You need to establish exposure times that suit your specific settings and paint density.
To do this, please prepare the sample exposure guide as described below and cover the blank PCB board with paint (
I have attached a stripe exposure image that you can print out on acetate fiber as your test mask and don't forget to double it and glue it together).
Divide it into 4 2 1/2 minutes time periods starting with a total of 10 minutes, and expose a sample plate, moving a piece of cardboard every 2 1/2 minutes so that a piece is exposed for 2 1/2 minutes, it was then exposed for 5 minutes, then 1/2 minutes, and finally 10 minutes.
Remove and clean the board using paper towels and paint thinners to see which areas become hard and which areas are not.
If almost all hard drives or all hard drives are removed, double or half the time and try again with a clean PC board.
Use these times to determine the recommended exposure time for the first board. Warning!
Once the mask is hardened, it is almost impossible to remove it, please carefully determine the exposure time before putting the board into this process.
If you are consistent when preparing your motherboard, you should not change the exposure time.
Use the time you get from the test to expose your mask.
After exposing the finished plate, remove it from the UV box, remove the welding mask, and then peel the acetate cover plate back.
You should see the paint attached to this piece of paper where the mat appears on your mask but not elsewhere on the board.
Now use paper towels and remove unexposed paint with paint thinners.
All paint should be removed from copper pads and vias instead of from traces, clean the boards before and after, and dry with paper towels.
To finish hardening, first check the unexposed area and remove any paint from the area that is never needed using a sharp tool.
Then place the plate in your UV exposure box and expose at least two to three times the original exposure time.
If needed, deal with the second party in the same way.
Drill out the hole through-the-
Hole Assembly and mounting holes.
I use the drill bit with the drill bit to process the wire diameter drill bit.
I find that if drilling is done before cutting to the final size, the board is easier to handle.
Using the circuit board contour line as the guide, trim the circuit board using rotating tools and cut-off wheels, file edges and circular corners, usually manually welding SMD parts first, then through holes, and finally through-the-Hole Assembly.
I made this device to hold down the SMD element while welding some washer bolts and nuts from several pins.
I applied a little liquid flux on the SMD pads, held the Assembly down, and then welded in place.
One trick for vias is to flatten a bit of the end of the wire with a pair of plyers so they don't fall from the passing holes.
Weld on the front, then bend the wire and weld on the back.
Your board is complete and ready for testing.
Although long is very helpful, I would like this explanation.
Please feel free to make constructive comments or ideas.
Thank you for taking the time to check out my process and have fun building an e-project.
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