Joe,
Having been a part of the committee that worked on 6016, I am sure the issue
of remaining foil thickness ever came up. Quarter ounce, and thinner foils
were not envisioned during the late 90's. Couple of processing points to
remember -
1. Will you have enough copper cross section to carry the current you
intend to put through the conductor?
2. The step after via drill and "laser ash removal" is metallization. That
step, either electroless copper or direct metallization, will include a
microetch step to remove copper, you must have enough copper left to allow that -
usually less than 0.1 mil or 2.5 microns. Half ounce foil, as pointed out
below is 17 microns or quarter ounce is 9 microns - should be enough to allow
microetch.
3. You did mention "foil", so I assume you are not trying to build up from
some additive or semi-additive copper feature from an embedded device like a
capacitor or resistor.
Denny Fritz
MacDermid, Inc
In a message dated 12/5/2007 7:30:10 A.M. Eastern Standard Time,
[log in to unmask] writes:
Joe;
From a laser drilling standpoint, we prefer to use a minimum of half
ounce copper for capture pad foil thickness. We have laser drilled a few
parts with quarter ounce capture pad foil, but it is tricky to do so as
the thin coppers buckle and damage easily from the localized heat of a
laser beam. We have also produced blind vias on plated up sub assemblies
that start with half ounce foil. We also routinely laser drill boards
for power management devices that utilize one and two ounce copper
foils. The thick foils are really hard to damage.
Dave Simonik
Laser Process Technician
Sanmina SCI Corp.
Owego NY Division
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Kane, Joseph E (US
SSA)
Sent: Tuesday, December 04, 2007 11:54 AM
To: [log in to unmask]
Subject: Blind Via Question
For HDI vias, what minimum target pad foil thickness is allowed after
hole preparation, prior to deposition and copper plating? IPC-6016
does not provide any requirements similar to those in
IPC-6012 Table 3-7 for HDI applications.
Joe Kane
BAE Systems
Johnson City, NY
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