allanw:
- I’m using the TLC5952 LED driver IC. I found a library that has one online but when I compared its footprint to the datasheet’s, the one I found was around 0.7mm in width off. But I don’t really know what I’m doing so perhaps I’m wrong here? The packaging datasheet is here: http://focus.ti.com/lit/ml/mpds029d/mpds029d.pdf and the grid on my screenshot is 0.05 mil.
TI is great about their package datasheets. Ensure you have the latest datasheet then look for the section titled ‘PCB footprint’, ‘Pad layout’, or similar. Create your package with their dimensions; usually there’s no need for buffering outlines. However, depending on soldering skill, you may want to make the pad sizes larger than their spec by 10%ish.
allanw:
2) The IC has a heatsink in the middle. How can I tell eagle to fill in the copper surrounding it better?
‘Better’? In your library’s package, I would create a rectangle with width 0 on the bottom copper layer, sized to TI’s package spec from ‘Footprint’ section of datasheet.
Alternative is to create polygon pours in your board file, but is ill-advised because it requires extra work and is prone to error.
allanw:
Also, I tried putting vias to let it go to the top layer ground copper but DRC gives me lots of warnings - they can be safely ignored, right?
In your DRC file, find the tab ‘Clearance’. Set the values for smd, pad, and via (only!) under heading ‘Same Signals’. This will eliminate the Overlap DRC errors. If you prefer not to change the DRC, you may ‘Approve’ the Overlap errors cause by vias on the same signals. When Approving, ensure the via signal name matches the top and bottom signal names.
allanw:
3) The tricolor LED pads are really close and huge. This only happened after I loaded sparkfun’s drc file. If I try to change the drill hole size then it gets under the 20mm limit. How can I fix this?
Change the drill size limit in DRC by going to ‘Sizes’ tab then finding ‘Minimum Drill’ field.
allanw:
4) Any other miscellaneous things that I’m doing wrong? I can attach my eagle files if they’d help.
Suggestions:
Eliminate the need for close tolerances by using SMD LEDs, such as a 5050 package.
Use ‘vector’ text style by default; set this in EAGLE settings.
Use text ‘ratio’ of 16 to 20% and size of 32mil or greater, to ensure best readability.
Use silkscreen line width greater than 12mil for best visibility and ‘obvious-ness’.
Use consistent pad types for headers (circle versus long) and a different pad type for pin 1 (such as square).
Route the ‘LAT’ and ‘BLANK’ signals further south and add more vias under the TLC part.
–
Ted
