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How to select a footprint to match component

Dhiraj
Hi guys! this is my first post in OrCAD forums. I am new to PCB design and even OrCAD. I have been trying to develop a 2-layer PCB.I am done with the schematic, but struck with assigning a proper footprint to the component. I was just wondering, OrCAD library has hell of footprints and much of them are quite similar. So, how do i know which footprint matches the component? Do I have to search all the footprints one by one in PCB editor and measure the physical dimensions till i get the proper footprint or is there a procedure to directly arrive at the requirement? For example, say i have used a 0.1uF capacitor in my circuit. OrCAD gives cap300.dra and cap400.dra footprints which are almost similar. Now, how do i decide whether the footprint i require is cap300.dra or cap400.dra.? I have the data sheet and hence cap's physical dimensions. Then should i measure physical dimensions of both the foot prints in PCB editor and then decide which is the perfect match? Can't it be done in a simpler way ?????
  • Anaxroche

    actually it depens on the components that in your hands or the components that you can buy easily.after the choosing component,datasheet will help you.package data and recommended footprint informations available in the datasheet.there is no relationship between a component and a footprint like this one for this one.it depends on your components and their dimension datas.this rule valid for general footprint descriptions.if you want,you can create special footprints that is belong to one component.

    but,if you ask,my component dimensions and everything is allright but which footprint name give me correct datas,good luck,just open related footprints and measure :)

  • Dhiraj
    Thanks for the reply Anaxroche! Actually i know this procedure and have been doing the same since i started designing PCB's i.e., referring corresponding data sheets and designing footprints on my own, in case there are no available footprints in the library. I have been suffering from sloth(laziness) these days and just wanted to know weather there is an easy way to directly arrive at the components footprint! Thought it would make my life easy! Any way, thanks for the reply! One more issue, my OrCAD libraries do not have certain thermal relief flash symbols like TR_180_150.dra. I have been trying to download such symbols but could not figure out where to get them! can u help me with this! SORRY if i am bothering you, but i am a newbie here! Thanks!
  • redwire

     Regarding flash symbols:  These are typically not included with any Cadence distributions but it's very easy to implement.

    Here are the basics for Flash symbols:

    1) Flashes are SYMBOLS and need to go in your symbols path (.dra)

    2) When compiled, flashes become  .fsm -- these need to be in your symbols path as well

    3) Open Allegro, File->New->Flash Symbol

    4) Add->Flash

    5) Fill in the Flash box (in this case: 150 inne, 180 outer, 20 spokes?)

    6)  Create Symbol

    7) Save, Done

  • Dhiraj
    Thanks redwire! I tried exactly the same way as you explained. After completing step 5, i get this error in the command window: "ERROR - Could Not Generate Shape E- (SPMHA1-66): Arc segment is outside of the extents."\n My settings are: THERMAL PAD DEFINITION: --------------------------------------Inner diameter: 150.00 --------------------------------------Outer diameter: 180.00 SPOKE DEFINITION: --------------------------------------Spoke width: 20.00 --------------------------------------Number of spokes: 3 or 4 --------------------------------------Spoke angle: 45.00 I've not checked the "Add center dot" option check box. I was not able to figure out the reason for the error! Any suggestion would be of great help!
  • Lakshmanan
    Hi Dhiraj, I saw all your conversations.The issue is the extents of the board is very less that your shape is not able to fit in.You need to increase the board extents.You can find the command under Setup-Design parameter Editor-Extents.You should be able to draw the shape once you have increased the value.
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