Re: gEDA-user: 2 newbie Qs

[kmk <kmk@xxxxxxxxxxxxxxx>]

Craig Niederberger wrote:

> What I'm struggling with is a footprint for a LM2575 with a TO-220-5 
> footprint, which has 5 pins, each pin with max dimensions 0.038 in x 
> 0.025 in

By coincidence I did a similar 5-pin TO220 footprint for my first geda
project a few months ago. It was called PENTAWATT and had the even pins
shifted. So there was more space between the pins.


> Element[0x00 "TO-220 5 pin" "" "" 10000 10000 0 4800 0 100 ""]
> (
> 	Pin[     0 0 6000 1400 6700 4600 "Pin_1" "1" 0x00000101]

This is 7 mil annular ring, 7 mil clearance to the next net and 3.5mil
clearance of the mask. However, the fabs that do my boards (Basista,
Beta-Layout) insist on 8 mil minimum annular ring for their regular
service. Clearance may be as low as 6 mil, though. Hole thickness 46 mil
 is a good value for TO220 type footprints. The pentawatt footprint on
my  little practice board was drilled according to the same numbers and
the component fits just fine.


> Element[0x00 "2mm header" "" "" 10000 10000 0 4800 0 100 ""]
> (
>	Pin[     0 0 5450 4900 7900 3000 "Pin_1" "1" 0x00000101]

This is 19.5 mil clearance to the next net, 12 mil annular ring and 12
mil mask clearance. 20 mil clearance is a lot. Are there large voltages
between the pins? I'd reduce mask clearance to 4 mil or less. After all,
only the pad is supposed to be exposed.


---<(kaimartin)>---

PS: This is my pentawatt footprint. I did it with the pcb GUI according
to a metric data sheet. Hence the random looking numbers for pin positions.

Element[0x0 "PENTAWATTV" "" "" 12590 46145 0 0 0 100 0x0]
(
	Pin[0 0 6600 2000 8600 4600 "" "1" 0x00000101]
	Pin[6693 -15748 6600 2000 8600 4600 "" "2" 0x00000001]
	Pin[13386 0 6600 2000 8600 4600 "" "3" 0x00000001]
	Pin[20079 -15748 6600 2000 8600 4600 "" "4" 0x0000001]
	Pin[26772 0 6600 2000 8600 4600 "" "5" 0x00000001]
	ElementLine [-7087 -14173 -7087 -33071 1000]
	ElementLine [-7087 -27559 33858 -27559 1000]
	ElementLine [28347 -14173 28347 -3937 1000]
	ElementLine [33858 -33071 33858 -14173 1000]
	ElementLine [-7087 -33071 33858 -33071 1000]
	ElementLine [1575 -14174 1575 -3938 1000]
	ElementLine [-1575 -14173 -1575 -3937 1000]
	ElementLine [25197 -14173 25197 -3937 1000]
	ElementLine [11811 -14173 11811 -3937 1000]
	ElementLine [14961 -14173 14961 -3937 1000]
	ElementLine [33858 -14173 23622 -14173 1000]
	ElementLine [10236 -14173 16536 -14173 1000]
	ElementLine [-7087 -14173 3150 -14173 1000]

	)


-- 
Kai-Martin Knaak
kmk@xxxxxxxxxxxx
http://lilalaser.de/blog


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