MAKING PCBs
Step One
As always, start with your Schematic with all parts and components labeled.
Step Two
Converting a schematic into a PCB or Perf Board layout is simple. First, remove the schematic symbols from the drawing to make it a little neater. You will want to be mindful of the spacing of the perf board and the actual size of the components you will be using. For this, you can use a perf board layout template like the one found at the bottom of the Electronic Job Sheet. Identify where your pads will be and use the same layout lines as the schematic to connect them. However, unlike the LED Blinker, when you are using an integrated circuit, the pin layout will likely be different than the schematic diagram. This is to make the schematic neater, but you cannot rearrange pins in real life. If you need help with integrated circuit pin layouts, see our Integrated Circuits page. So after you consider the new pin arrangement, follow the following steps of transforming your schematic into a PCB. First, the tracers should have a width to them. Real tracers have width. Second, you have to remove overlapping lines. The schematic drawing and PCB Layout are 2D representations of a 3D object, however, the PCB layout actually has to be built so you have to pretend that crossing lines are actually touching in a PCB layout. To prevent crossing tracers where they shouldn't, you will have to break one of the rules above. You will either have to run a trace between the pads of a component or add a space for a jumper. In this example, we created extra pads for a jumper. Finally, you will have to add a spot for your power source. Be sure to double-check the polarity of all components and the orientation of the ICU, Integrated Circuit Unit.
Step Three
Since you are drawing the PCB Layout on the copper of the PCB, which is actually the bottom, you will have to mirror the PCB Layout in order for the pins of your ICU and polarity of your polarized components to line up.
Step Four
Grab a piece of Copper-Clad PC Board and cut it to the approximate size needed using a shear. In this case, we will need a piece about an inch and a half by two inches
Step Five
Using a Fine-point Black Sharpie, Carefully draw a copy of your PCB layout onto the PC Board directly on the copper. Be sure to keep the sizes of all the hole locations and component sizes exact. (Remember, these holes will have to line up with real parts.)
Step Six
Drill a hole in the corner of the board and thread a fishing line through it. This will be used to lower and raise the board into the Etching Tank.
Step Seven
Carefully lower your board into the etching Tank. This tank is filled with Ferric Chloride, an acid that will dissolve the copper that is not covered by sharpie on the board. Be careful with this step and always follow proper safety procedures when dealing with this step. You should be wearing safety goggles and gloves to protect you from any splash from the acid. When unsure about the use of a chemical, be sure to refer to its Material Safety Data Sheet (MSDS.) The tank should have a heater and bubbler turned on to speed up the etching process. Check that your board is clear of copper except for the part covered by sharpie about every five minutes.
Step Eight
When you remove the board, you have to remove the sharpie and check that your PCB tracers are clean and still there. Depending on how well you applied the sharpie and how long the board had to be in the acid, there is a chance the acid crept up under the ink of the sharpie and disrupted your tracers. The sharpie can be removed with steel wool and you should check that every tracer has continuity to where it needs to with a multimeter. If there are any tracers that are not connected, you can fix them by pulling solder if they are small enough gaps.
Step Nine
Unlike the perf board, a PCB does not have any holes in it until you make them. This is to keep the board clean looking and you will drill just the holes you need. Using a Rotary Dremel, Dremel Workstation, and PCB Drill Bits 0.7mm you can drill each hole in the center of the pads that you need. Be sure to do this slowly and carefully because the drill bits are very small and fragile.
Step Ten
Using your PCB layout as a guide, insert your components into the board where they need to go. Be sure to pay attention to the polarity and orientation of each components. Keep in mind that since you are placing the components in through the side of the PCB without the tracers, your components will be mirrored to the original drawing.
Step Eleven
Solder the components into the board and you are finished! If you did everything correctly, the metal detector should work as soon as you turn it on! Be creative with its case! Is can be anything as long as it isn't metal!
Check out a Blog on making PCBs using alternative methods made by our very own MakerLesson's student, Sahil.