EE380 – Electronics I
Lab 4
Fall 2013
Printed Circuit Boards (PCBs) Objective The goal of this lab is to introduce students to printed board circuit design. The design portion of this lab is to layout a power supply using software downloadable from: www.expresspcb.com. Each group will do their own PCB layout and provide printouts of their layouts. Download the Express PCB Layout and Schematic ee380power.pcb and ee380power.sch from the class website. You will link this schematic to the layout that you create. This is a one-week lab. Background Information 1. The total amount of real-estate that each group will be given for the power supply circuit is 1.9" by 2.2" (that is, 1.9 in. x 2.2 in.). Everything on your power supply must fit. 2. The most important consideration in layout of a power –supply circuit is the layout of the power and ground traces. Make sure that the traces are wide enough to carry the current. A good ROT for a ¼ oz copper board is 0.100"/amp. If your board has extra room, make all power and ground traces even wider. Since our power supplies will supply as much as 600mA, we will be using at least 0.060" traces for all power signals. 3. The minimum space between traces is 0.010". If you go less than that, the traces might short out during manufacturing. 4. The minimum space between pads is 0.030". A pad is a circle (or oval or square) with a hole in the middle of it for soldering components, like resistors or ICs. I think you need the extra space (0.030") for soldering. Otherwise, you might end up accidentally shorting out two pads when you solder their components in place. 5. We have two tools for measuring distances: an engineering ruler (in 1/10th’s of inches) and a much more precise digital caliper (in inches or mm – use inches for this lab). 6. You will draw on three layers: a. Top layer (red) is for all traces except for VSS (the negative rail). b. Bottom layer (green) is for VSS only. The bottom layer will also have huge rectangles of metal, effectively creating a ground plane. c. Silk screen layer (yellow) will not be fabricated, but is helpful when doing the layout. It is used for naming each part. Page 1
EE380 – Electronics I
Lab 4
Fall 2013
Name: ____________________________________________________ Note: You are encouraged to work on pre-lab questions prior to lab. However, the lab TA, Kashif, will give you a fresh piece of paper for you to work the pre-lab quiz, once you are in lab. Pre-lab quizzes are done individually, not as a group.
Pre-lab Questions Week1 (10 points) 1. What is the suggested width for a trace that carries 2 A of current?
2. What is the minimum space between two traces that are 0.080" wide?
3. What is the minimum distance between two pads that have a diameter of 0.140"?
4. What traces go on the top (red) layer?
5. What tools are used to measure distances?
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EE380 – Electronics I
Lab 4
Fall 2013
Exercise I: Layout of circuit The objective of this exercise is to layout a power supply circuit that will be designed and tested in the next lab and will be part of your final project. The schematic is on the last page of the lab. 1. Verify that the frame on the silkscreen layer (yellow) to be a 1.9" by 2.2" rectangle. 2. The 4 nylon standoffs go in the four corners. Use 0.200" round pad with 0.150" holes for the standoffs. 3. Create a pattern of holes with a silkscreen box for a 3-contact terminal strip. Use 0.100" pads with 0.046" holes. Measure the distance between pins on the terminal strip using a decimal ruler or caliper. What is the correct spacing of the pads? What are the outside dimensions (length and width) of the terminal strip? 4. Draw 4 silkscreen traces to make a box that size. Number the pads 1, 2, and 3. Use the “Group to make PCB component” command (under Component menu) to combine the pads and the box together. (See the figure below.) Finally, place the terminal strip along one side of the board.
5. Place the power adapter connector (J1) on the upper of left edge of the PCB board. It is important that you place connectors on the edge of the board. After step 5, your board might look like one of the boards below:
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EE380 – Electronics I
Lab 4
Fall 2013
6. Place all your parts down with identifying number (e.g., R1, U2, LED2…). Here are some parts you will need: a. Resistors: 1/4 Watt (lead spacing 0.35"), pad: 0.056", hole: 0.029" b. 1N4003 Diode: 1N4007 (lead spacing 0.4"), pad 0.075", hole: 0.040" The square pad is the negative terminal. c. 1N914 Diode: DO-35 (lead spacing 0.3"), pad 0.056", hole: 0.029" The square pad is the negative terminal. d. Radial Electrolytic Cap: Find the largest electrolytic capacitor that comes in your kit. What is the spacing between leads? Use calipers to measure them. The square pad is the positive terminal. Place this large capacitor near one of the corners of your layout. e. Tantalum Cap: What is the spacing between leads? The square pad is the positive terminal. f. 741 Opamp: Use the Dip – 8 pin socket (DIP = Dual In-line Package) g. LM317: Semiconductor TO-220 with no mounting hole. Place the LM317 on the edge of the PCB. Extra room is required for the heat sink. h. Custom Potentiometer: i. Potentiometer – Bourns series 3386F (DigiKey 3386F-101-ND) ii. “Ungroup” iii. Move holes where needed iv. “Group to make PCB component” i. LEDs: LED – T 1 (lead spacing 0.100"), pad 0.056", hole 0.029" j. Custom Resettable Fuse: i. Cap – Lead Spacing (What is the spacing between leads?) ii.
“Ungroup”
iii. Change pads to pad 0.100", hole 0.046" iv. “Group to make PCB component” k. 2-Pin Test Connector (J2): i. Draw two round pads of dimensions pad 0.075", hole: 0.040". ii. Space them 0.100"apart. iii. Number the pads 1 and 2. “Group to make PCB component” Page 4
EE380 – Electronics I
Lab 4
Fall 2013
7. Now label your components by double-clicking on them and typing things like R4, C2…. You want the labels to match the schematic. Label the custom parts. 8. Link Your Schematic (downloaded from class website) to your PCB layout. 9. Now wire your circuit using the following guidelines: a. VS1, VS2, VC, and VDD (on top side, red) require wide traces because they will carry 600mA. Use 0.060". These traces are drawn wide on the schematic. b. VSS is on the bottom side. Use 0.100". The VSS trace should be huge whenever possible and is drawn very wide. c. Draw large rectangular regions that are green to create a ground plane. Don’t make the entire bottom side green, or else you would short out every pad. Leave some room near components (~ 0.100"), in case you have to add holes to your board after fabrication. Make the bottom side 35% - 60% green. d. All signal wires, including SGND and VADJ, (on top side) can be smaller traces: use 0.030". 10. Now label your circuit. Labels on the silkscreen layer will not appear on your board. Put the labels below in metal (top side or bottom side), making sure they don’t touch traces or pads. a. Label input /output signals (on top side) using text height: 0.050". b. The only input /output label on the bottom side is VSS (green & backwards) c. To label your names and project name, use text height: 0.070". (Your name and project name can also be on the bottom side.) d. As space on your board permits, label polarities on capacitors and diodes (with ‘+’ signs) and pin 1 on ICs using text height: 0.050". 11. Print out your layout to review it We will need three printouts for your lab report: a. Top-Side, Enlarge to Fit Page, Portrait b. Bottom-Side, Enlarge to Fit Page, Portrait c. Silk-screen, pads, and Text on Top Side, Enlarge to Fit Page, Portrait 12. Save your PCB layout with a filename that identifies you, for example, Kashif_Altaf.pcb 13. Have the TA review your design.
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EE380 – Electronics I
Lab 4
Fall 2013
14. Your layout must be complete and sent to TA Kashif Altaf by Saturday, October 10th 2012 @ 5:00PM as follows: TO:
[email protected],
[email protected], or
[email protected] SUBJECT: PCB LAYOUT ATTACHED FILE: Name1_Name2.PCB for example: Kashif_XYZ.pcb Exercise II. Summary and Discussion. The objective of this exercise is to summarize and discuss this 1-week lab. Write 0.75 to 1 pages, using one-and-a-half line spacing, 12-point type (like this document). At the top of the page, place names of the group and the title of the lab. Indicate which teammate is serving as the recorder for this lab. Then write: 1. An introductory paragraph that describes the main objectives of the laboratory, listing the major exercises you did. 2. Two paragraphs discussing several things that you learned, such as a new measurement technique or a new troubleshooting technique. Of particular interest are things that you struggled with, e.g., a bad component or wire that needed to be changed, etc. What to Include in the Lab Report: 1. (19 points) The summary and discussion. Indicate who is serving as the team Recorder. 2. (1 point) A printout of the Express Schematic that you used to create your PCB. 3. (20 points) Three printouts from expressPCB of your layouts, as described in the lab. Be sure to include printouts for each group of one-to-two students. 4. (60 points) The PCB file that is submitted to the TA on-time, again, one for each group. For every error (correction) the TA has to make for you, points will be subtracted from your score, roughly 2 points per correction.
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