This might be what you are looking for.  Please excuse me if there is an
error in this text as I'm still half asleep.


Refer to IPC2221, section 9.0 &  IPC-2222 section 9.2 for complete information.

To find the minimum through-hole land size, a worst-case land-to hole
relationship must be established.  The following equation from IPC-2221
will do that.

Where:
Copper weight = 1 oz and number of layers are 8 or less.  (see table 9-1 in
IPC-2221)

For internal layers:
a = the drilled hole diameter ( see table 9-3 in IPC-2222)
For external layers:
a = maximum diameter of the finished hole (see table 9-3 in IPC-2222)

b = minimum annular ring requirements = 2 mils

c = standard fabrication allowance = 8-16 mils (see table 9-1 in IPC-2221)

For example, take a 20 AWG wire that is 38 mils in diameter at its maximum,
8 layer PWB.

The maximum diameter of the finished hole would be 38 + 6 (hole to lead
space) + 3 (tolerance)  = 47 mils.  The nominal diameter would be 38 + 6 =
44 mils.

The drilled hole diameter is 44 + 6  =  50 mils.

Minimum through-hole land size = a + 2*b + c
Internal land = 50 + 4 + 10 = 64 mils
External land = 47 + 4 + 10 = 61 mils
Remember, these are the minimum land sizes and they can be made larger.

In IPC-2222, section 9.2.2 Plated-Through Holes, the minimum and maximum
finished hole size is discussed.  It states that the maximum hole size is
less than or equal to the minimum lead diameter plus 28 mils (level A) and
that the minimum finished hole size is greater than or equal to the maximum
lead diameter plus 10 mils (level A).

The following methods calculate the minimum land size for a typical
DIP-I.C. with leads as follows.  Width = (15 mils  23 mils), Thickness = (8
mils  15 mils), Diagonal = (17 mils - 27 mils).

Using the IPC-2221 formula

For internal lands
Minimum land size = a + 2*b + c

Where:
a = drilled hole diameter
b = minimum annular ring
c = fabrication allowance

drilled hole diameter = maximum diameter of finished hole +6 mils (depends
on type of finish).

a =   51 mils
b = 2 mil (internal)
c = 14 mils (8 layers or less)
c = 16 mils (10 layers or more)
c = add 2 mils/oz of Cu for Cu > 1oz

Number of Layers 10 8
a42 mils42 mils
2*24 mils4 mils
c16 mils14 mils
Min land size =62 mils60 mils

Using the IPC-2221 formula

For external lands
Minimum land size = a + 2*b + c

Where:
a = maximum diameter finished hole
b = minimum annular ring
c = fabrication allowance

maximum diameter finished hole = minimum lead diameter (17 mils) + 28 mils
= 45 mils.

a = 45 mils
b = 2 mil (external)
c = 14 mils (8 layers or less)
c = 16 mils (10 layers or more)
c = add 2 mils/oz of Cu for Cu > 1 oz.

Numbers Layers 10 8
a45 mils45 mils
2*24 mils4 mils
c16 mils14 mils
Min land size =65 mils63 mils







At 09:26 AM 3/29/2004 -0600, you wrote:
>Fellow TechNetters,
>
>     Can someone guide me to an IPC document that make reference to
>Finish Hole Size
>versus lead acceptable lead diameter with respect to ROUND, RECTANGULAR
>and SQUARE
>Leads.   I have a case in which the square lead deformed the PTH and
>minimal solder
>fillet is exhibited inside the barrel.   At least in my opinion.
>
>In advance I thank you for your timely response in this matter.
>
>Victor,
>
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Donald Kyle C.I.D.+

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