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Sometimes when I order PCBs from a board house, I omit the bottom silkscreen for budgetary reasons. When I place surface-mount chips on the bottom of the board, I then end up with a footprint that doesn't indicate the chip orientation. This is annoying because it means that I need to verify the component placement and orientation during assembly, and this allows for errors when placing the parts.

How can I clearly indicate pin 1 with the remaining layers in a way that will be clear but not significantly impact the PCB size or cause issues when soldering? I'm assuming that I always have access to a solder mask layer and a copper layer.

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You might be doing onesy-twosy builds. But if you are doing any volume at all, then doing double-sided SMT is probably a bigger cost adder than a second silkscreen layer. –  The Photon Jan 2 at 17:32
    
@ThePhoton This is purely for one-off builds that will be hand assembled. I understand the cost trade-offs change when you start talking about automated manufacturing. –  W5VO Jan 2 at 17:40
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4 Answers 4

up vote 29 down vote accepted

Have a differently shaped solder mask on pin 1.

For surface mount processors, you could have the pin 1 pad be noticably longer than the others.

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I've also seen (and it's built in to the supplied libraries in Altium) pad 1 have rounded corners (in copper) while all the others are rectangular. –  The Photon Jan 2 at 17:29
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I add a small dot in the copper layer near pin 1 but if the routing is too dense it may not be possible

enter image description here

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alexan_e - Look at your profile - you may wish to save an image of your reputation before the year gets much older - It looks like this :-) –  Russell McMahon Jan 3 at 11:07
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@RussellMcMahon I haven't realized it, thank you for sharing. Now there is only stevenh standing in the way for a full house...maybe next year LOL :-) –  alexan_e Jan 3 at 11:28
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Unless there are tight tolerances for the pad layout use a different shape pad for pin 1. i.e. oval instead of square.

Edit: the difference between this answer and previous answers is the difference between a solder pad and solder mask.

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This solution doesn't seem to be different from what Adam has proposed in his reply. –  alexan_e Jan 2 at 21:38
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I agree with the previous suggestions for altering the pin 1 shape, whether that be in soldermask only, or the pin as a whole (Soldermask & Copper).

However, for aiding with the always inevitable debugging and troubleshooting later-on, pin shape & component pin 1 markings may be difficult to identify. It may be preferable to use a small "fiducial-like" marking on the board to emulate silkscreen. This will simply be a small copper marking (dot or line) with a soldermask opening over it.

Another idea may be to align all your components to have their Pin #1 in a specific orientation (usually handy for polarized 2-pin SMT devices, diodes, caps etc.)

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