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PCB Design Guidelines

Below are a number of Guideline Rules to follow and keep in mind when designing PCBs. These are general rules that apply for the most PCB fabricators, but it is advisable to check with your fabricator.

Board Size
PCB manufacturers have a maximum size board they can handle. Typically this is also their panel size. The PCB fabrication house's panel size is also important when mass producing boards. In this situation one would want to fit as many boards as possible on a panel with as little wasted board space as possible (in order to reduce costs). Normal board spacing for routing (how boards are separated on a panel) is 0.3", plus there is typically a 1.0" to 2.0" border on the board for handling it during processing.

Board thickness may also be specified. A standard thickness and type of board is .062" FR4. Other typical board thickness are .010", .020", .031", and .092".

Trace Width and Spacing
The chemical and photographic processes used to produce a PCB put requirements on the minimum width of trace and the minimum spacing between traces. If a trace is made smaller than this minimum width there is some chance it will open (no connection) when manufactured. If two traces are closer together than the minimum spacing there is some chance they will short when manufactured. These parameters are usually specified as "x/y rules", where x is the minimum trace width and y is the minimum trace spacing. For example, "8/10 rules" would indicate 8 mil minimum trace width and 10 mil minimum trace spacing. These rules (especially spacing) apply to any metal on the PCB, including pad to track spacing and line widths for strings on the PCB.

Typical modern process rules are 8/8 rules with values as small as 2/2 rules being available. For Press-n-Peel people have had success using 12/12 rules, but values a little larger are easier to make work consistently. However, keep in mind that the board must be soldered and a trace within 8 mils (8/8 rules) of a pad is easier to short than one with greater spacing when hand soldered. For hand soldering 10/10 rules are much easier to solder (if the design density can allow spacing this large).

Pad Sizes
The biggest issues with pad size are solder ability and manufacturability. Solder ability is really just a matter of skill and will not be discussed here. Manufacturability is concerned with whether or not the pad will be broken when the hold is drilled in it. This is mainly a function of the accuracy of the PCB manufacturer's drilling. If a drill hole is slightly off center the pad may be broken at one edge possibly leading to an open in the circuit. A standard requirement for pad sizes is a 5 mil annulus. This means there must be .005" all around the hole (i.e. a 28 mil hole would require a 38 mil pad). Something a little larger than this (maybe 10 mils) is recommended for solder ability. AP Circuits states they have had relatively consistent success with a 2.5 mil annulus (i.e. a 20 mil hole with only a 25 mil pad), but they don't recommend it.

Hole Sizes
Most PCB manufacturers have a wide selection of drill (hole) sizes available. Some charge per drill size used, others offer a standard set of drill sizes for no charge and then charge for any non-standard drill sizes. AP Circuits uses the latter approach. When choosing a hole size remember that the plate-through will cause the hole to effectively be more narrow. The plate-through thickness varies from .001" to .003". AP Circuits' plate-through thickness is approximately .015" (meaning the "finished hole" diameter is 3 mils smaller).

Standard Drill Sizes

Drill Number	Hole Size	Finished Hole Size
70	.028"	.025"
65	.035"	.032"
58	.042"	.039"
55	.052"	.049"
53	.0595"	.056"
44	.086"	.083"
1/8"	.125"	.122"
24	.152"	.149"

Hole Density
Hole density is purely a cost issue. The more holes there are on a board the more wear and tear manufacturing will put on the equipment (and thus the more the board will cost). Most PCB manufacturers have a maximum hole density and boards with greater density are charged more. For AP Circuits, there is a per hole charge for densities above 24 holes per square inch.

Drill Chart

Drill No.	Inches	Drill No.	Inches	Drill No.	Inches
80	.0135	53	.0595	27	.1440
79	.0145	52	.0635	26	.1470
78	.0160	51	.0670	25	.1495
77	.0180	50	.0700	24	.1520
76	0200	49	.0730	23	.1540
75	.0210	48	.0760	22	.1570
74	.0225	47	.0785	21	.1590
73	.0240	46	.0810	20	.1610
72	.0250	45	.0820	19	.1660
71	.0260	44	.0860	18	.1695
70	.0280	43	.0890	17	.1730
69	.0292	42	.0935	16	.1770
68	.0310	41	.0960	15	.1800
67	.0320	40	.0980	14	.1820
66	.0330	39	.0995	13	.1850
65	.0350	38	.1015	12	.1890
64	.0360	37	.1040	11	.1910
63	.0370	36	.1065	10	.1935
62	.0380	35	.1100	09	.1960
61	.0390	34	.1110	08	.1990
60	.0400	33	.1130	07	.2010
59	.0410	32	.1160	06	.2040
58	.0420	31	.1200	05	.2055
57	.0430	1/8"	.1250	04	.2090
56	.0465	30	.1285	03	.2130
55	.0520	29	.1360	02	.2210
54	.0550	28	.1405	01	.2280

dBm - Volts - Watts Conversion

dBm	V	Po	dBm	V	Po	dBm	uV	Po
+53	100.0	200W	+7	0.50	5mW	-37	3.2
+50	70.0	100W	+6	0.445	4mW	-38	2.85
+49	64.0	80W	+5	0.40	3.2mW	-39	2.5
+48	58.0	64W	+4	0.355	2.5mW	-40	2.25	0.1uW
+47	50.0	50W	+3	0.320	2.0mW	-41	2.0
+46	44.5	40W	+2	0.280	1.6mW	-42	1.8
+45	40.0	32W	+1	0.252	1.25mW	-43	1.6
+44	32.5	25W	0	0.225	1.00mW	-44	1.4
+43	32.0	20W	-1	0.200	0.80mW	-45	1.25
+42	28.0	16W	-2	0.180	0.64mW	-46	1.18
+41	26.2	12.5W	-3	0.160	0.50mW	-47	1.00
+40	22.5	10W	-4	0.141	0.40mW	-48	0.90
+39	20.0	8W	-5	0.125	0.32mW	-49	800
+38	18.0	6.4W	-6	0.115	0.25mW	-50	710	0.01uW
+37	16.0	5W	-7	0.100	0.20mW	-51	640
+36	14.1	4W	-8	0.090	0.16mW	-52	570
+35	12.5	3.2W	-9	0.080	0.125mW	-53	500
+34	11.5	2.5W	-10	0.071	0.10mW	-54	450
+33	10.0	2W	-11	64		-55	0.40
+32	9.0	1.6W	-12	58		-56	351
+31	8.0	1.25W	-13	50		-57	320
+30	7.10	1.0W	-14	45		-58	286
+29	6.40	800mW	-15	40		-59	251
+28	5.80	640mW	-16	35.5		-60	225	0.001uW
+27	5.00	500mW	-17	31.5		-61	200
+26	4.45	400mW	-18	28.5		-62	180
+25	4.00	320mW	-19	25.1		-63	160
+24	3.55	250mW	-20	22.5	0.01mW	-64	141
+23	3.20	200mW	-21	20.0		-65	128
+22	2.80	160mW	-22	17.9		-66	115
+21	2.52	125mW	-23	15.9		-67	100
+20	2.25	100mW	-24	14.1		-68	90
+19	2.00	80mW	-25	12.8		-69	80
+18	1.80	64mW	-26	11.5		-70	71	0.1nW
+17	1.60	50mW	-27	10.0		-71	65
+16	1.41	40mW	-28	8.9		-72	58
+15	1.25	32mW	-29	8.0		-73	50
+14	1.15	25mW	-30	7.1	0.001mW	-74	45
+13	1.00	20mW	-31	6.25		-75	40
+12	0.90	16mW	-32	5.8		-76	35
+11