Printed Circuit Board Design Avnish Kumar Dept. of Electrical & Computer Engineering University of Connecticut September 26, 2016 (Based on Prof. Sung Y. Park’s slides, Fall 2014)

Printed Circuit Board ? A printed circuit board (PCB) mechanically supports and electrically connects the electronic components using conductive tracks, pads and other features etched from copper sheets laminated onto a non- conductive substrate. PCBs can be single sided (one copper layer), double sided (two copper layers) or multi-layer. Conductors on different layers are connected with plated-through holes called Vias. Advanced PCBs may contain components - capacitors, resistors or active devices - embedded in the substrate. 4

Multi-layer PCB design 2 Layer PCB design: Top layer and bottom layer 4 Layer PCB design: Top, Bottom, and two middle layers. FR4 (glass-reinforced epoxy laminate sheets) pre impregnated, is a fiber weave impregnated with a resin bonding agent. Solder mask (green/red) Copper trace Silkscreen 3

Three Elements to be considered Components : - How to select components? - What values are needed? - What kind of package will be available/are needed? Printed Circuit Board : - Schematic Design - PCB Layout Design - Prototype board Case or Box for the prototype board : - Purchase or build by yourself 4

Printed Circuit Board Design Schematic Design PCB Layout 5

Printed Circuit Board Design A PCB as a design on a computer (left) and realized as a board assembly populated with components (right). The board is double sided, with through-hole plating, green solder resist and a white legend. Both surface mount and through-hole components have been used. 6

Key Elements of a PCB Pads are where the components are soldered to the PCB. Traces are the copper tracks that connect pads together. Via are small holes through the board that link a bottom and top trace together electrically. Traces on the same layer cannot cross, so often, when you are laying out a PCB, you need to jump from one layer to another. 7

Key Elements of a PCB Silk-screen refers to any lettering that will appear on the final board. Solder-mask is a layer of insulating lacquer that covers both sides of the board except where there are pads. 8

PCB design procedure {Specific/Measurable} goals  Design specification Circuit diagram Schematic design  Select components Check the dimension  Build a footprint  Make a PCB library  Add parts Export schematic design to layout design Route all connection Design rule check Generate Gerber files and drill file and zip them Upload zip file to PCB order website - - Visualize; This is a good time to be thinking about your design from a system level - finishing your project and giving up in frustration - Gerber: open ASCII vector format for 2D binary Images 9

Dimension: mil (imperial unit) vs mm (metric) PCB Library design Component datasheet Dimension: mil (imperial unit) vs mm (metric) 1 inch =1000 mil, 1 mil = 0.0254 mm 1 mm = 39.3700787 mil DIP component and connector: 100 mil or 2.54 mm Symbol in schematic vs Exact dimension in Layout Pad number should be matched in schematic symbol and layout footprint DIP = Dual in-line Package. 10

PCB Library dimension example Male header 11

Tips for PCB design Keep traces straight, Try to avoid 90o turns use two 45o’s. Double, even triple check layout, Having a fresh pair of eyes look it over, “measure twice, cut once” idea. Trace thickness & spacing Spacing of at least .010”, 0.030” for In-house ~0.025” per 1 Amp carrying lines, Don’t use anything smaller than 0.010” for traces, 0.030” for In-house milling. Try to keep all connections on one side of PCB Take into account component package 12

Tips for PCB design Keep traces straight Try to avoid 90˚ turns, use two 45˚ turns instead Double (even triple) check the layout Have a fresh pair of eyes look over it “measure twice, cut once” idea Trace thickness & spacing Spacing of atleast 0.01 inches; 0.03 inches for In-house ~0.025 inches per 1 Amp carrying lines Don’t use anything smaller than 0.01 inches for traces; 0.03 inches for In-house Try to keep all connections on one side of the PCB Take into account the component packages 90 deg – longer traces, more impedence, RF reflection, less compact packing, harder to etch. avoid 4-way connection points make a very clear dot where two wires form an intersection 13

Free PCB design program EAGLE Cross-platform, Free with limitations, upgrades from $70 – $1640. A powerhouse in the hobbyist world, EAGLE probably has the most community support. KiCad Free and open source, no limitations Express PCB Free, no limitations. ExpressPCB is backed by ExpressPCB so this makes it very easy to send your design for manufacture. DesignSpark PCB Free, no limitations Eagle - good community support 14

Making PCBs Layout your circuit / circuits Check out http://www.expressPCB.com for some great tips on component layout and power distribution. Layout is more of an art. Tight spaces Lots of connections Make a 2 level board into a 3 level with vias 15

PCB Design Example 16

Top and Bottom Layer 17

Middle Layers(2nd & 3rd) 18

PCB Design Assignment Every senior deign team needs to design one PCB during the fall semester The number of components used should be more than 5 (connectors, surface mount components, through-hole components, ICS etc.) The number of layers should be 2 or more Report due date is November 19th 2016 Report should contain: Schematic, layout design, and free DFM check result† of the PCB. † https://www.my4pcb.com/net35/FreeDFMNet/FreeDFMHome.aspx 19