After reading all threads, I have to add that we never had problems with
Press-Fit connectors.
We only specified a tighter tolerance ( drill size ) of +/- 0.002", which
makes the fab house take exception, as that is tight for a plated hole. It
is fine for NPTH, as in a tooling pin. The manufacturer of the press-fit
connector will specify their requirements on their drawing.
No one mentioned wether the press-fit problem was in hole size variation or
positional accuracy. Only positional accuracy was discussed, as I recall so
I assume that is where the problem was.
As said, any worthy fab shop & worthy CM can do it, if communication between
you & them is there......
Good discussion gang......
Regards
TDK
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Roger Stoops
Sent: Thursday, May 05, 2005 11:36 AM
To: [log in to unmask]
Subject: Re: [TN] Through hole drill accuracy
Good point and well taken, hadn't thought of that...
That must be why I'm in design and not in fabrication. And those poor
fabricators that see my designs...ah, well.
Regards,
Roger
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Jeffrey Bush
Sent: Thursday, May 05, 2005 1:13 PM
To: [log in to unmask]
Subject: Re: [TN] Through hole drill accuracy
Well, lets consider a tooling pin that is undersized in a tooling hole
or drill bed bushing that is oversized. As you drill the panels will be
moving randomly and you will see variations hole to hole based on this
tolerance relationship. Sometimes the mismatch will be in your favor
and sometimes you will see the extent of the gap. This however cannot
be ignored in the consideration of capability for drilling as these
frequencies will be seen at one point or another in the resulting
products.
Jeffrey Bush
Director, Quality Assurance and Technical Support
VERMONT CIRCUITS INCORPORATED
76 Technology Drive - POB 1890
Brattleboro, Vermont 05302
Voice: 802.257.4571.21 Fax: 802.257.0011
http://www.vtcircuits.com
-----Original Message-----
From: Roger Stoops [mailto:[log in to unmask]]
Sent: Thursday, May 05, 2005 10:33 AM
To: [log in to unmask]
Subject: Re: [TN] Through hole drill accuracy
Thanks for the clarification. However, for a given pattern or grouping
of plated holes on a board, pin tolerances would have little if any
effect, would they? The only effect they would have is when moving a
board stack from one machine to another, correct?
If a particular press-fit connector required both plated and non-plated
holes, the additional tolerances added by the use of pins could become a
real concern. But those new-fangled drill machines with vision
capability could help negate that, yes? Excellon has some purdy
machines...
Regards,
Roger
-----Original Message-----
From: Jeffrey Bush [mailto:[log in to unmask]]
Sent: Thursday, May 05, 2005 10:09 AM
To: TechNet E-Mail Forum; Roger Stoops
Subject: RE: [TN] Through hole drill accuracy
What about other factors in drilling beyond machine accuracy - pin
tolerance, pin to tooling tolerance, and pin to bed tolerance. These
factors are also constituents in the overall drill accuracy beyond the
machine tolerances native to the process.
Jeffrey Bush
Director, Quality Assurance and Technical Support
VERMONT CIRCUITS INCORPORATED
76 Technology Drive - POB 1890
Brattleboro, Vermont 05302
Voice: 802.257.4571.21 Fax: 802.257.0011
http://www.vtcircuits.com
-----Original Message-----
From: Roger Stoops [mailto:[log in to unmask]]
Sent: Thursday, May 05, 2005 9:30 AM
To: [log in to unmask]
Subject: Re: [TN] Through hole drill accuracy
If the alignment is off by 2mils or more, sounds like your fab house
needs to check their drilling machine, or else use a better, more
accurate one than typically used. The issue is one of positional
accuracy plus repeatability. If a machine has a drilling accuracy of
+/-.001, positional accuracy of +/-.0005, and repeatability of +/-.0005,
then the total accumulated tolerance can be as large as +/-.002.
Sound like you need to specify a location tolerance (true position) of
+/-.0015 (or better) for the holes in question. The wider the tolerance
for hole diameter, the narrower the tolerance for location accuracy, and
vice versa, for press-fit connectors. IPC-2221 9.2.2 says you can
expect +/-.002 for fabs built to level B. Asking for Level C would give
you +/-.0015 tolerance. (If I'm missing something, somebody *please* set
me on the straight and narrow...)
Use of GD&T (IPC-2615) would help in specifying what you really want,
because tolerance zones with GD&T are round, not square as in the
(unfortunately) typical drawing practice.
All said and done: it's up to you to specify hole size, tolerance, *and*
accuracy for your design. If you don't specify accuracy, the board
vendor may provide you with what's easy for them to make, to the widest
tolerances possible.
Best Regards,
Roger
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Scott Lefebvre
Sent: Wednesday, May 04, 2005 6:10 PM
To: [log in to unmask]
Subject: [TN] Through hole drill accuracy
I have looked profusely at IPC-6012 for a specification I could not
find. I need to know if there is a specification for PTH drill accuracy
and repeatability. We have a press-fit connector we are having problems
with. The component manufacturer tested one of our boards and said the
alignment is off 2 mils or more in some locations. I could not find
what is the spec in IPC to reference to, could someone please point me
to the correct document I should look at.
Sincerely,
SCOTT L
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