Goliath Fall 2016
PCB Layout
By: Dylan Hong (Design and Manufacturing Engineer)
Approved by Kristen Oduca (Project Manager)
Introuction
Requirement: Goliath shall have a custom PCB
For CDR, our goal was to create a PCB Layout using EAGLECAD from the schematic that the ENC created. Our PCB consist of speakers and RBG LEDs. The PCB is double sided. The following will explain the process of creating our custom PCB.
PCB Layout
Our PCB layout will be double sided and will include a ground to ground plane.
When creating our PCB layout, we must first determine the placement and location of the PCB on our model. Since we would like to display our RGB LEDs, the most ideal location would be in the front of the top panel of our Goliath. Next, we figure out the dimensions of the location and create our outline of the PCB. In our case, the PCB outline dimensions were 53.34mm x 16.41mm.
Second, we place the components accordingly and determine which components will be placed on the top and bottom layer. The top layer will consists of one 100 ohm 805 resistor, one NPN transistor, five SMD RGB 5050 LEDs that will display the distance and the direction of the Biped and a trimpot to adjust the volume of our speaker. The bottom layer will include a PWM LED controller (PCA9685), ten 10 ohm 805 resistors, five 47 ohm 805 resistors, two 2.2k ohm 805 resistors, one 0.1 uF capacitor, one 10 uF capacitor, one servo header, one speaker, two sensor headers, and an I2C header mount. Next, we route the designated air wires to their respected components. When routing, it is best to have the wires at a 45 degree angle and to use circle vias that are 0.3048mm in diameter. As you begin to route, you may come across wires that are causing conflict with another wire. This is where vias become useful because it will allow you to bypass that wire by entering another layer. It is always better use less vias as possible, but if necessary it is okay to place them in the preferred areas. In some cases, even creating vias won’t help when encountering conflicting wires. Another method of simple routing can be changing the orientation of a component. Initially, I placed the PWM IC horizontally, which cause the routing to become much more difficult; so in order to make my life easier, I simply rotated the orientation to portrait mode. As you can see in the PCB images, the rotating of the PWM IC proved to have a much cleaner and simpler routing of the wires. My initial PCB Layout is shown in Figure 1.
Figure 1 – Initial PCB Layout
Our cleaner layout is shown in Figure 2.
Figure 2 – Second PCB Layout
Now to make the routings even simpler, do not bother routing the ground wires. Instead, add a ground plane to the top and bottom layers, this will allow the grounded wires to connect directly to the ground planes. The ground plane is shown in Figure 3.
Figure 3 – Ground Plane
Now that the PCB is mostly complete, it is mandatory to run a Design Rule Check (DRC), this will check the PCB for any errors such as overlays and clearances. Since we are ordering the PCB from Oshpark, it is important to run the Oshpark DRC along with the default DRC to ensure that our PCB meets the requirements of the manufacturer. Furthermore, we added labels to our PCB to easily distinguish the components. How the actual board will look like is shown in Figure 4.
Figure 4 – PCB Board
Finally, I sent the PCB to my division manager, the customer, and the president for approval and purchase. Purchasing a stencil is not required, but it will make soldering SMD components easier to handle and cleaner.
Conclusion
After creating the PCB, this changed how the Goliath would look like since the LEDs need to be displayed. This moved our design process forward.