I think a gap exists in understanding what I am saying. The designer
should specify what the finished dimensions are for all factors and let
the PCB house get there based on their specific process capabilities.
Size, circuit geometry, aspect ratio, etc. all have an impact on the
resulting plating deposit, which is further complicated by many
differing plating processes equipments and techniques. This has nothing
to do with the function of the board and the need for the PCB house to
understand this. If the desired finished result is articulated on the
drawing, the PCB house can process the boards to meet the end-product
requirements. If a minimum hole size is needed, in the case of a via,
the drawing should state this and not allow the hole to finish below the
minimum.
Don't short change the PCB house - we have a fair understanding of many
of you products and more importantly how to get the there for the OEM.
Supposing the designer will understand the multitude of variables that
are inherent in PCB fabrication is much more remote than the house
having a handle on thermal and capacity management obstacles.
Jeffrey Bush
Director, Quality Assurance and Technical Support
VERMONT CIRCUITS INCORPORATED
76 Technology Drive - POB 1890
Brattleboro, Vermont 05302
Voice - 802.257.4571 ext 21
Fax - 802.257.0011
<http://www.vtcircuits.com/>
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Werner Engelmaier
Sent: Wednesday, April 26, 2006 3:35 PM
To: [log in to unmask]
Subject: Re: [TN] Drill specification
Hi Jeff,
You say: "...the PCB house ... may opt to alter the drill size based on
several factors -size, geometry, aspect ratio, etc."
This assumes, that the PCB house knows something about the operational
use of
these PCBs-rarely the case, or that it knows more than the designer what
is
needed-too often the case.
However, for knowledgeable designers that design a high-reliability
product,
particularly for severe operational environments, and who know the
capabilities of the PCB house, it is much better to specify the drilled
hole diameter-
again all too often not the case.
Werner
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