In case nobody else answered your questions...

 -----Original Message-----
From:   Leonard Alexman [mailto:[log in to unmask]]
Sent:   Wednesday, March 06, 2002 11:48 AM
To:     [log in to unmask]
Subject:        [TN] Thermals, plane clearances etc.

Hello All,

I am trying to determine the exact meaning of the IPC spec 2221
sections 9.1.2 thru 9.1.4 and have many questions hopefully
someone  can answer.

From section 9.1.2 "A".

1. Is maximum hole size the drilled size or the finished hole size ?
Finished size for plated holes,  drilled size for non-plated holes (ref 2221
section 9.1.1)

2.  The annular ring uses a 0.05 MM value for the annular ringsize.
In table 9.2 in spec IPC2221 0.05mm is for external Supported annular rings
shouldn't the value be 0.03mm since the plane is an internal layer
Table 9-2 gives the figure for Internal Supported Annular Ring as 0.03mm
(Amendment 1 gives the figure of 0.025mm)

From Section 9.1.3 Figure 9.1.

1. The .25MM minimum for the nonfunctional land is this what should be
used to create the outer ring size on a thermal connection ?
At this point in time I discovered you meant to also say "IPC-2222".  Yes.

2. Is the value "B" - standard manufacturing allowance the same as
fabrication allowance ?    Yes.

3. For value "A" - electrical clearance - how are these values determined ?
See Table 6-1.  (Your board fabricator may also have a minimum spacing
requirement. Can make inspection a real pain.)  Could be the same (or
greater) than your trace-trace spacing.

From section 9.1.3.1.

1. In figure 9-2 on the bottom right side is shows A + B see fig 9-3.
Shouldn't that be
figure 9-1 ?   Probably.   Also why is this even mentioned if the clearance
area is
determined by
hole diameter and fabrication allowance ?   Clearance area is determined by
electrical clearance + fabrication allowance, and what the board vendor can
produce.  IPC was just trying to be thorough in their documentation.

2. Is the hole diameter (max) the finished hole size of the drill size ?
Think "finished hole size" for plated holes, "drill size" for non-plated
holes.

Lenny ALexman


Roger M. Stoops,  CID   [log in to unmask]

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