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--- ee:pcbfoametching [2021/10/04 18:02]
21960@students.hsrw
+++ ee:pcbfoametching [2022/02/16 18:43] (current)
21960@students.hsrw
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 WORK IN PROGRESS
+CHANGE PICTURES TO CORRECT EQUIPMENT
+EDIT INFORMATION FOR NEW ETCHING CHEMICAL
+FORMAT UVMASCK PRODUCTION
@@ Line 8: / Line 14: @@
 ===== Introduction =====
-This instruction is about producing printed circuit boards (PCBs) from already prepared designs. There are two major techniques for PCB manufacturing. For prototyping purposes it is popular to use a special milling machine for PCBs. The faculty uses a LPKF ProtoMat S62 in its [[ee:electricalworkshop|electrical workshop]]. EAGLE board designs are exported to gerber and excellon files and after making some adjustments in a CAM tool like CircuitCAM designs can be used for milling out copper-clad boards. The machine isolates all traces on the board and drills holes where necessary.
+ This instruction is about producing printed circuit boards (PCB) from prepared board schematics to component placement.
+The technique of PCB manufacturing employed in this lab is that of chemical etching. it is a five step procedure:
-The technique which is covered here employs a chemical process to create PCBs. To put it simply it is a four step procedure:
+  - Create PCB mask for UV exposure.
-  - prepare development and etching solutions
+  - expose PCB to UV light while protecting certain areas with a mask
-  - expose board to uv light while protecting certain areas with a mask
+  - develop PCB schematic using sodium hydroxide
-  - develop board using sodium hydroxide
+  - etch PCB schematic using iron chloride
-  - etch board using sodium persulfate
+  - clean PCB of residue using alcohol wipes
-The industry also these principle steps for mass production of PCBs.
@@ Line 27: / Line 31: @@
   * [[https://www.reichelt.de/-p23424.html?|sodium persulfate]]
   * cleaner (e.g. ethanol or aceton)
-  * purified water
   * [[https://www.reichelt.de/-p89770.html|toner compressor]]
   * [[https://www.reichelt.de/-p9486.html|solderable protective spray]]
   * paper towels
+  * A4 printer paper
+  * A4 transparent foil
 Optimally this process is executed in a chemistry lab. This is the list of needed tools:
-  * [[https://www.reichelt.de/-p23418.html|etching machine]] (if you have exacly this machine, torx screwdrivers are handy)
+  * [[https://www.reichelt.de/-p23418.html|etching machine]] (if you have exactly this machine, torx screwdrivers are handy)
-  * UV expusure unit, preferably with light bulbs from both sides
+  * UV exposure unit, preferably with light bulbs from both sides
-  * magnetic stirrer (optional)
-  * thermometer (optional)
-  * precision scale
-  * bowl, slighly bigger than your PCB
-  * beaker big (2 l)
-  * beaker small
-  * scoop
-  * glass stirrer
-  * cotton pad
-  * stapler
-  * ruler
   * scissors
   * plate shear
@@ Line 53: / Line 47: @@
   * lab coat
   * gloves
-===== Procedure =====
+  * Printer
-==== Masks for uv exposure ====
-The PCB design should already be finished and the artwork should be ready. If not there is a separate guide on how to [[pcbuvmasks|create masks for uv exposure]].
 ==== Safety instructions ====
@@ Line 65: / Line 59: @@
   * etchant / sodium persulafte (Natriumpersulfat, Na<sub>2</sub>S<sub>2</sub>O<sub>8</sub>)
   * ethanol (C<sub>2</sub>H<sub>6</sub>O)
-  * distilled (purified) water (H<sub>2</sub>O)
 Make yourself familiar with safety precautions for these substances and read the safety data sheets for them.
 As stated in the beginning the following steps are normally performed in a proper lab after special security instructions and under supervision.
 ==== Set up developing and etching solutions ====
@@ Line 75: / Line 72: @@
 Put on your safety equipment. This includes glasses, lab coat and gloves. Make yourself familiar with the tools.
-  - Make sure you have a bowl like shown in <imgref bowl>. It will be used as container for the development solution. You should also have a 500 ml beaker (see <imgref beaker>) for measurement, a glass rod for stirring and a weighing boat.
+RINSER
-  - Fill the beaker with 250 ml distilled water.
-  - Fill 5g sodium hydroxide into your beaker. In order to get the right amount use the precision scale and a weighing boat. Close the container of sodium hydroxide as sodium hydroxide is hrydrophilic.
+Removal & disposal of water from Rinser
-  - Stir the liquid in the beaker with a glass rod until everything is dissolved.
-  - Pour the solution into the plastic bowl.
-  - Make sure you have a big glass beaker like shown in <imgref beaker>, a magnetic stirrer (see <imgref magnetic_stirrer>), a thermometer and a small beaker with sodium persulfate.
-  - Fill the big beaker with approximately 1.6 liter of distilled water.
+DEVELOPER
-  - Add 300g sodium persulfate to it.
-  - Use the magnetic stirrer (if available) to heat the big beaker up and help dissolving the sodium persulfate at the same time (setting 4 / 4). As etching etching works best above 40°C (and below 50°C). Try to heat the solution up until it reaches 40°C.
+Removal & disposal of developing solution from developer
-  - If there is no magnetic stirrer available, stirr the solution and continus. The etching machine also has a heater, it will just take longer.
-  - When the solution is ready turn off the magnetic stirrer and pour the solution **carefully** into the etching device.
+New Developing solution for developer
-  - Turn on the heating and air compressor of the etching device by plugging it into the electric outlets.
+Etcher
+Removal & disposal of etching solution from etcher
+New etching solution for Etcher
 <imgcaption bowl|Bowl>{{:ee:bowl.png?200}}</imgcaption>
 <imgcaption beaker|Beaker>{{:ee:beaker.png?120}}</imgcaption>
 <imgcaption magnetic_stirrer|Magnetic stirrer>{{:ee:magnetic_stirrer.png?200}}</imgcaption>
+===== Procedure =====
+==== Masks for UV exposure ====
+-The PCB design and layout should be completed by students and comply with both ERC and DRC respectively.
+-Place ground planes on both top and bottom of PCB design (use polygon feature in eagle) to limit the amount of etching required.
+-Select top layer of PCB and show only tracks, ground planes, Via's and Pad's and selected marking's to be shown on PCB, note anything that is shown will be etched on to the PCB.
+-Save using Print to PDF ensuring the color is black, size is A4, removing attributes from the bottom of page and saving with a recognizable file name i,e PCB_top.
+-Select Bottom layer of PCB and show only tracks, ground planes, Via's and Pad's and selected marking's to be shown on PCB, note anything that is shown will be etched on to the PCB.
+-Save using Print to PDF ensuring the color is black, size is A4, removing attributes from the bottom of page, SELECT THE MIRROR FUNCTION and saving with a recognizable file name i,e PCB_Bottom.
+-At least one side of PCB mask must be mirrored due to the geometric nature of applying the mask.
+-Print both sides of PCB design on the top and bottom of an A4 paper. To do this print one side of PCB design on A4 sheet of paper, than place printed sheet of paper back in the printer's paper tray, ink side up with the already printed PCB design at the bottom of the paper tray.
+-Check to see if design is correctly aligned, To do this fold paper in half and check for correct pad and via locations.
+-If all is correct than repeat printing process with projector paper.
+-cut projector paper and align PCB schematic on top of each other ensuring the inked sides of the sheets are inside together, and secure in place with sticky tape (the inked sides are a mat black in color and can be distinguished by touch).
+-Ensure there is no or minimal alignment of the PCB designs as this may result in defective PCB manufacture. (Pro tip cut sheet off center i,e have one side bigger than the other. this allows for easier alignment and sticky tape application).
+-Well done you have now created your PCB Mask and are now ready to start with the UV exposure process.
 ==== UV exposure ====
-  - Get the transparent foils containing your PCB design.
-  - Apply some density spray to both foils. Make sure to apply it on the side with the printing. This step has to be executed in a well ventilated room, if available  do it under a fume cupboard.
+  - Open your PCB mask and apply some density spray to the inside of both foils. Make sure to apply it on the side with the printing. This step has to be executed in a well ventilated room, if available  do it under a fume cupboard.
   - Wait for the density spray to dry. The black areas should be clearly darker now.
-  - Use scissors to cut out your design. Leave a big surrounding area, as you will nedd it for stapeling.
+  -  Get a piece of photosensitive base material (FR4 in this case) for exposure. It should only be slightly bigger than your design. If necessary cut it with a plate shear.
-  - Place the foils on top of each other. The sides with the printing on it have to be facing each other (the board will be in between of the foils later).
+  - Remove the blue protection foil (see <imgref RemoveProtectionFoil>) on both sides, be aware this may produce some black residue near the edges of the material. In most cases this will be negligible but may cause the material to stick.
-  - Staple the foils together while trying to align them perfectly.
+  - Avoid exposing the unprotected plate to sunlight (all UV sources). Best to have a special room for this step(use the etching room as it has been set up for this), if not available make sure to not waste to much time.
-  - Check the alignment. Misalignments will probably result in defective PCBs later.
+  - Put the copper plate between the transparent foils and open the drawer of the UV exposure device, lift the glass panel and gently place copper plate in the middle of the drawer.(see <imgref UVExposureDevice>, <imgref BoardUnderPlate>).
-  - Get a piece of fotensensitive base material (FR4 in this case) for exposure. It should only be slightly bigger than your design. If necessary cut it with a plate shear.
+  - Align copper plate within transparent foil as desired and gently close the lid.
-  - Remove the blue protection foil (see <imgref RemoveProtectionFoil>) on both sides.
+  - Turn it on apply the vacuum, wait for the vacuum to go up (to 0.3 with our device, compare to <imgref CheckVacuum>). The vacuum prevents things from moving and presses foils and PCB together. once secure close the drawer.
-  - Avoid exposing the unprotected plate to sunlight (all UV sources). Best to have a special room for this step, if not available make sure to not waste to much time.
+  - **Beware:** For your own safety avoid looking into the UV lights. The device is to be started only when the drawer is closed!
-  - Put the copper plate between the transparent foils and put both under the glass plate of the uv exposure device (see <imgref UVExposureDevice>, <imgref BoardUnderPlate>).
+  - Set the exposure time to two minutes and thirty seconds (the display should read 2-3-0), start the device by pressing the knob once.
-  - **Beware:** For your own safety avoid looking into the uv lights. The device is to be only turned on when closed!
+  - When the time is up the lights will automatically be turned off, open the drawer and release the vacuum.
-  - Turn it on and wait for the vacuum to go up (to 0.3 with our device, compare to <imgref CheckVacuum>).  The vacuum prevents things from moving and presses foils and PCB together.
+  - Open the lid and get out the exposed board, and close the drawer.
-  - Set the exposure time to two minutes and thirty seconds (the display should read 2-3-0), make sure the bottom lights are also enabled if you are making a two sided PCB and start the device by pressing the knob once.
-  - When the time is up the lights will automatically be turned off and the vacuum will be released.
-  - Open the device and get out the exposed board.
 <imgcaption RemoveProtectionFoil|Remove protection foil>{{:ee:removeprotectionfoil.png?direct&200}}</imgcaption>
@@ Line 119: / Line 156: @@
 ==== Developing and etching the board ====
-  - Remove the exposed board from the foils.
+  - Remove the exposed board from the foils, note the copper foil will still appear blank.
-  - Put the board  into the prepared bowl of the development solution. Stir it with a stick.
+  - Place the board into the purpose design clamp, ensuring board is sitting correctly in the notches and tighten sufficiently by turning knob. Conduct a little shake test to ensure board is secured.
-  - Brown residues from the exposed parts of the board should start to appear after a couple of seconds. Stir until the process seems to stop and take it out immediately. Do not leave the board in for longer than 90 seconds maximum.
+  - Start developer machine and wait for the solution to begin circulation.
-  - Rinse the board thoroughly with (purified) water.
+  - place board in solution using the rack hanger of the clamp ensuring the complete board is submerged within the developing solution.
-  - Check the temperature of the etching solution, it should be above 40 and below 50 degrees C. If not, keep waiting.
+  - Brown residues from the exposed parts of the board should start to appear after a couple of seconds.
-  - Mount the board to the grey retainer (see <imgref Holder>). To speed up the procution process you may want to  mount two boards at the same time.
+  - continue to develop until the mask is clearly visible and the brown exposed photo resist has been stripped. this process should take around 1-3 minutes.
-  - Submerge the board(s) in the tank.
+  - Rinse the board thoroughly with water using the rinsing function, ensure the water supply has been turned on.
-  - Wait for the etching process to complete. You may have to wait a couple of minutes before something seems to be happening but from this point it should be going quite fast and obvious.
+  - check the board to ensure the mask is clearly defined and there are no significant defects on the mask and shut down developing machine.
-  - Take out the board when etching is complete. Do not wait to long as it will affect the protected traces as well if you wait too long.
+  - start the etching machine and wait for the etching solution to rise as a foam (if solution isn't sufficiently foaming than, open fresh beer, taste to ensure its quality stuff, no Veltins please! Add minute amounts to etching solution until desired foaming has occurred).
-  - Rinse the board(s) thoroughly with (purified) water.
+  - place board in etching foam using the rack hanger of the clamp ensuring the complete board is submerged within the etching foam.
-  - Repeat these steps until all team members have a PCB.
+  - Wait for the etching process to complete. You may have to wait a couple of minutes before something seems to be happening but from this point it should be going quite fast and obvious. To check etching please rinse in neutralization solution to allow better inspection.
-  - Shut down pump and heating.
+  - Continue etching until complete. this process should take around 4-6 minutes. Do not wait to long as it will affect the protected traces as well if you wait too long.
-  - Use ethanol and paper tissue to remove the remaining photoresist from the board(s). Be thorough.
+  - Rinse the board thoroughly with the rinsing function.
-  - Let the board(s) dry. You can also use compressed air to speed things up.
+  - turn off etching machine.
-  - Clean the lab equipment, rinse everything with water.
+  - dry the board using paper towels
+  - Use alcohol wipes to remove the remaining photo-resist from the board. Be thorough, this will show up as blackness on wipe.
   - Dispose of waste properly.
+Congratulations your board is now ready to place and solder components.
+.
 <imgcaption Holder|Holder>{{:ee:holder.png?200}}</imgcaption>
+Via's Component Placement and soldering
+PCB's use two types of technologies for connecting components that require different ways of soldering being THT and SMD. due to the nature of the PCB construction used in the labs will require via's to also be manually placed.
+Via's
+Available sizes for punching via's in the university: 0.6 mm (drill 0.9 mm, pad 1.5 mm) and 1.0 mm (drill 1.5 mm, pad 2.5 mm).
+To place a via in your PCB
+- drill the correct size hole for the desired size via at the wanted location.
+-correctly select and set the manual via press in place on a steady surface.
+-place the desired sized via so it sits on the suitable sized pin of the press with the flange of the via resting at the bottom (use of tweezers recommended).
+-Place PCB so via sits in correct position and gently but firmly press down handle of press.
+Through hole Technologies THT
+Surface Mounted Technologies SMD

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