PCB Design Notes

20090212 Notes from MCDSP64A PCB work.


Olimex seem fairly restrictive on clearances:

Minimum tracks and spaces: 0,203 mm (0,008")

"For instance if your traces are wide enough (>20mils) the board can be manufactured with etch resist single silkscreen priniting operation instead of dry film lamination, exposure, developing."


"Turnaround time: 3-5 WORKING DAYS if traces/spaces >= 0,254 mm (0,010"); 15 WORKING DAYS if traces/spaces < 0,254 mm (0,010") "

MCDSP64A rules:

RJ 6p6c sockets:

  • upped the RJ12 PTH pins to 9mm (Drilled size as Olimex treat em as drilled not plated sizes)
  • with pads 1.4 x 1.7mm
  • no traces run between the pins as we cannot get clearances

Minimum trace size 0.33mm

Design rules:

All clearances initially set to 0.25 except board outline at 1mm then progressively up to 0.3mm until no errors except for dsPIC TQFT64.

dsPIC TQFT64 Pattern per MChip specification DS0049AR 0.8mm pin to pin, 0.25mm pin to pin clearance.  Edit clearance to 0.3mm (pin width from 0.55 to 0.5mm (pins are 0.3mm wide on the package.

Good notes on analogue / digital separation: http://www.embedded-computing.com/articles/id/?2573

Lots of tips to reduce EMI on PCB layout: http://www.hottconsultants.com/tips.html

Hole / pad sizes etc: http://en.wikibooks.org/wiki/Practical_Electronics/PCB_Layout:

Very good info in subkitting designs to a fab house: http://www.pcbfast.com.au/cam-information/

http://www.goldphoenixpcb.biz/special_price.php: Minimum clearance and trace width 7mil, minimum hole size 15mil.

Mount holes: M3 Hex Standoffs & Bolts require just under 6mm diameter free..

Conversion Units (useful for identifying which pattern to use for an existing component)

Note: Not sure if 1 mil is actually 0.0254mm (.01 inches) as opposed to 0.025 ..

so to convert mm to mil (for PCB pattern editing, 1 mm = 40 mil so multiply by 40..)

10 0.25
40 1mm
200 5mm
400 10mm






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