{ Electronics production }

PCB board material can use many kinds of materials, such as FR1, FR2, FR3, FR4, and so on.

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FR1

FR-1 is a hard, flat material that consists of a thin layer of copper over a non-conductive phenolic resin.

FR-1 is primarily used for making circuit boards. The thin copper layer can be milled or etched away, leaving traces to which electronic components can be soldered.

Unlike FR-4, which is fiberglass-based and generates dangerous glass-shard dust when milled, FR-1 is safe to use if you keep it away from your eyes, lungs, and skin. We recommend vacuuming up the debris after you’re done milling (never blow on it).

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FR2

FR-2 is a NEMA designation for synthetic resin bonded paper, a composite material made of paper impregnated with a plasticized phenol formaldehyde resin, used in the manufacture of printed circuit boards.

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FR3

FR3 is also basically FR2. But instead of phenolic resin it uses an epoxy resin binder.

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FR4

The base material, or substrate, is usually fiberglass. Historically, the most common designator for this fiberglass is "FR4". This solid core gives the PCB its rigidity and thickness. There are also flexible PCBs built on flexible high-temperature plastic (Kapton or the equivalent).

So, in terms of health it is preferable to use FR1, however here in my country Mexico, it is difficult to find this type of PCB, the most common and economical that you can find in any store is the FR4.

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Copper

The next layer is a thin copper foil, which is laminated to the board with heat and adhesive. On common, double sided PCBs, copper is applied to both sides of the substrate. In lower cost electronic gadgets the PCB may have copper on only one side. When we refer to a double sided or 2-layer board we are referring to the number of copper layers (2) in our lasagna. This can be as few as 1 layer or as many as 16 layers or more.

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Soldermask

The layer on top of the copper foil is called the soldermask layer. This layer gives the PCB some color. It is overlaid onto the copper layer to insulate the copper traces from accidental contact with other metal, solder, or conductive bits. This layer helps the user to solder to the correct places and prevent solder jumpers.

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Silkscreen

The white silkscreen layer is applied on top of the soldermask layer. The silkscreen adds letters, numbers, and symbols to the PCB that allow for easier assembly and indicators for humans to better understand the board. We often use silkscreen labels to indicate what the function of each pin or LED.

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Terminology

Now that you've got an idea of what a PCB structure is, let's define some terms that you may hear when dealing with PCBs:

• Annular ring

  - the ring of copper around a plated through hole in a PCB.

• DRC

  - design rule check. A software check of your design to make sure the design does not contain errors such as traces that incorrectly touch, traces too skinny, or drill holes that are too small.

• Drill hit

  - places on a design where a hole should be drilled, or where they actually were drilled on the board. Inaccurate drill hits caused by dull bits are a common manufacturing issue.

• Finger

  - exposed metal pads along the edge of a board, used to create a connection between two circuit boards. Common examples are along the edges of computer expansion or memory boards and older cartridge-based video games.

• Mouse bites

  - an alternative to v-score for separating boards from panels. A number of drill hits are clustered close together, creating a weak spot where the board can be broken easily after the fact. See the SparkFun Protosnap boards for a good example.

• Pad

  - a portion of exposed metal on the surface of a board to which a component is soldered.

• Panel

  - a larger circuit board composed of many smaller boards which will be broken apart before use. Automated circuit board handling equipment frequently has trouble with smaller boards, and by aggregating several boards together at once, the process can be sped up significantly.

• Paste stencil

  - a thin, metal (or sometimes plastic) stencil which lies over the board, allowing solder paste to be deposited in specific areas during assembly.

• Pick-and-place

  - the machine or process by which components are placed on a circuit board.

• Plane

  - a continuous block of copper on a circuit board, define by borders rather than by a path. Also commonly called a "pour".

• Plated through hole

  - a hole on a board which has an annular ring and which is plated all the way through the board. May be a connection point for a through hole component, a via to pass a signal through, or a mounting hole.

• Pogo pin

  - spring-loaded contact used to make a temporary connection for test or programming purposes.

• Reflow

  - melting the solder to create joints between pads and component leads.

• Silkscreen

  - the letters, number, symbols, and imagery on a circuit board. Usually only one color is available, and resolution is usually fairly low.

• Slot

  - any hole in a board which is not round. Slots may or may not be plated. Slots sometimes add to add cost to the board because they require extra cut-out time.

• Solder paste

  - small balls of solder suspended in a gel medium which, with the aid of a paste stencil, are applied to the surface mount pads on a PCB before the components are placed. During reflow, the solder in the paste melts, creating electrical and mechanical joints between the pads and the component.

• Solder pot

  - a pot used to quickly hand solder boards with through hole components. Usually contains a small amount of molten solder into which the board is quickly dipped, leaving solder joints on all exposed pads.

• Soldermask

  - a layer of protective material laid over the metal to prevent short circuits, corrosion, and other problems. Frequently green, although other colors (SparkFun red, Arduino blue, or Apple black) are possible. Occasionally referred to as "resist".

• Solder jumper

  - a small, blob of solder connecting two adjacent pins on a component on a circuit board. Depending on the design, a solder jumper can be used to connect two pads or pins together. It can also cause unwanted shorts.

• Surface mount

  - construction method which allows components to be simply set on a board, not requiring that leads pass through holes in the board. This is the dominant method of assembly in use today, and allows boards to be populated quickly and easily.

• Thermal

  - a small trace used to connect a pad to a plane. If a pad is not thermally relieved, it becomes difficult to get the pad to a high enough temperature to create a good solder joint. An improperly thermally relieved pad will feel "sticky" when you attempt to solder to it, and will take an abnormally long time to reflow.

• Thieving

  - hatching, gridlines, or dots of copper left in areas of a board where no plane or traces exist. Reduces difficulty of etching because less time in the bath is required to remove unneeded copper.

• Trace

  - a continuous path of copper on a circuit board.

• V-score

  - a partial cut through a board, allowing the board to be easily snapped along a line.

• Via

  - a hole in a board used to pass a signal from one layer to another. Tented vias are covered by soldermask to protect them from being soldered to. Vias where connectors and components are to be attached are often untented (uncovered) so that they can be easily soldered.

• Wave solder

  - a method of soldering used on boards with through-hole components where the board is passed over a standing wave of molten solder, which adheres to exposed pads and component leads.

To weld we use the following welding station, which we set at 341º, recommended temperature to start welding as a rookie and do not overburden the welding.

Previously, I already knew how to weld but only normal components, never something so small. You must have patience and have slept well the night before, otherwise your hand will shake a lot. In the following photos you can see my first surface mount welding.

The Roland Modela MDX-20 is a desktop 3D scanning and milling machine that is compatable with many popular 3D CAD software. The machine can be used to mill ABS, acrylic, wood, plaster, styrene foam, chemical wood, wax, and light metals such as aluminum and brass. The Modela software can accept .STL, .DXF, and .MDJ file types.

Specifications

• Maximum Working Area: 203.2 mm (X) x 152.4 mm (Y) x 60.5 mm (Z)
• Maximum Table Load Weight: 1 kg (2.2 Ibs)
• Compatible Materials: ABS, acrylic, wood, plaster, styrene foam, chemical wood, wax, plaster, polyacetal, polycarbonate, Sandomur SS, aluminum, brass
• Weight of Unit: 13.7 kg (30.2 Ibs)

Then we use the Model MDX-20 3D Milling Machine to record and cut the practice as a team.

It is necessary to change the tip if you want to engrave or cut a PCB, for this we must remove the tip you have, using an allen key and carefully loosen the screw to release the tip and remove it. Help me with a sponge so that the tip would not fall flat and flatten.

As part of the practice, we take the following file in .PNG format to be able to record it on the machine.

Then we enter the site fabmodules.org which is a web application that allows us to convert our circuit design .PNG to .RML, which can be interpreted by the Modela MDX-20 3D Milling Machine.

First we must load our image, then select the output format, which should be .RML (Roland mill), then select the type of processing, which in this case must first be the engraving, PCB Traces (1/64)

We configure the parameters in the right panel. We apply offset, we tested with 4 so that the tracks would not be so thin and thus facilitate welding.

After obtaining the .RML file, we must load it to the model, for this we follow the following steps:

1. Start the machine with the power button
2. Place the engraving tip and adjust it
3. Press the view button to locate the tip in the coordinate 0,0
4. Lower the tip on the Z axis with the UP and DOWN buttons in order to locate it better
5. 5. Open the RolandMDX_20ControlPanelCode software
6. Adjust the tip closest to the PCB, to such an extent that you begin to make the engraving. With the help of a sheet of paper, we place it just below the tip and lower it little by little until it tears the blade and releases
7. In the software we establish the coordinates of origin X and Y
8. We load our file in format (.RML)
9. The program will begin to make the engraving of our design

After this, I decided to engrave my PCB based on Brian's FabTinyISP.

This are files for the traces and the board outline:

So upload the original file to the fabmodules web application and proceed to convert it to .RML

Then we opened the Roland machine software and loaded our file.

Everyone recorded their PCB on the same plate, but there was a problem, the model did not allow us to cut the PCB, so we decided to use a tape to cut each plate.

After cutting my PCB, I had to sand to remove burrs and clean the tracks. This is the result:

Next, I had to profile my PCB by cutting it as it should have been with the Modela. So help me with a Dremel and a press to hold it.

• 1x ATtiny45 or ATtiny85
• 2x 1kΩ resistors
• 2x 499Ω resistors
• 2x 49Ω resistors
• 2x 3.3v zener diodes
• 1x red LED
• 1x green LED
• 1x 100nF capacitor
• 1x 2x3 pin header

To verify, the resistances were measured with the multimeter. In order to help me to weld and not confuse the pieces, I decided to put them in order stuck a tape.

So I soldered the components on my PCB

The result was the following, but I was wrong in 2 resistances, so I had to desolder them to be able to fit them correctly and weld them well.

Finally, to verify that my USB-PCB worked I had to burn it with the help of the Tiny AVR Programmer, which helps to program the ATtiny45 and 85.

Download the firmware source code and extract the zip file (on Linux, unzip fts_firmware_bdm_v1.zip). Open your terminal program and cd into the source code directory.

Run make. This will build the hex file that will get programmed onto the ATtiny45. When the command completes, you should now have a file called fts_firmware.hex. If the command doesn't complete successfully, something is wrong with your toolchain installation. Consult the error messages for information that will help you debug it.

In Mac the process was somewhat different since I had to install Crosspack, besides I have to mention that it is necessary to modify the file for your microcontroller.

• { fts_mini_traces.png }
• { fts_mini_cut.png }
• firmware source code