Hi, Moonman and All, especially Ian, Brad and Jeff,
I'm trying to correlate the information each of you has shared with me, and
I want to ask one or two more questions (first one aimed mostly at Ian, I
think):
Given the ductility information given by Earl and IPC 2221/6012, and
Ian's gen on copper cracking under temp cycling, do you know if the T/C
failure info was obtained using IPC 2221/6012 boards and the Cu plating
thickness of 1 mil? If not, do you know what boards were used? BTW, our
hole copper thickness is between 0.7 mils and 1 mil as a rule.
Do you have an opinion one way or the other about retaining
'non-functional' pads on inner layers when considering copper ductility
in holes? Do they help or hinder? I contributed to the recent TechNet
thread on this issue and strongly favour retaining them, but my
Technical Director is now seriously considering taking them out to use
the space for trace routing, etc (functional stuff). He know my opinion
and reasons, but other design considerations may make him over-rule my
humble manufacturing experience.
My profound thanks to you all again for coming to the rescue. Earl, what's
a comumn?
Peter
Earl Moon
<[log in to unmask] To: [log in to unmask], DUNCAN
M.COM> Peter/Asst Prin Engr/ST Aero/ST Group@ST Domain
cc:
03/06/02 Subject: Re: Pads, holes, traces and Class 3
08:29 PM field reliability
Peter,
It just doesn't seem too hard to me. 5:1 aspect ratio holes, especially the
diameter vs board thickness you describe is completely acceptable.
Actually,
it is in the preferred comumn.
You know we've talked about this before realizing cu plating thickness and
ductility requirements must be met as .001" thickness, and all the rest
entailed in 6012, and ductility well exceeding 10%. Nothing will make the
hole walls come apart using this criteria to the extent all else meets
6012's figure 3.5 and associated requirements in that section. Of course,
laminate integrity is important as well and voiding requirements in the
laminate evaluation area cannot exceed that which is specified. Don't want
any voids propagating into cracks extending into the thermal evaluation
zones/holes and causing cracks.
Copper foil, for very high reliability boards, such as some Class III
types,
also should be very ductile. This means using rolled annealed copper
instead
of ED type. We need the plated hole interface to internal layers to be
capable of withstanding thermal stress and shock as well. Also, as
indicated
in section 3, clear requirements must be met for hole plating to surface
conductors.
Actually, instead of more discussion on my part, IPC 2221, etc., and 6012
cover all the ground, and much more, you are concerned about. There's
little
else to say.
Very best wishes on your endeavor and its success,
Earl
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