HI, Werner,
Thanks for the support. Are you suggesting, though , that retention of
non-functional pads in small-diameter holes contributes to the barrel
cracking, particularly when plating is thin? Or are you saying that barrel
cracking is now the more common problem in small-diameter holes, that the
"non-functional pad" issue has fallen off in importance and that n-f pads
do not contribute to barrel cracking?
Myself, I can imagine that thin plating could crack when connected to n-f
pads and subjected to themp cycling, especially if the copper is not
ductile enough. How then to support hole plating and prevent its
deformation through resin recession and/or hole pull-away? Or are these
defects not significant in purely interconnect via holes? Is removal of n-f
pads to prevent barrels cracking better than keeping them to give support
to the barrel plating?
Do you know what, if any, correlation there is between plating thickness,
hole diameter, aspect ratio, number of layers and the point where barrel
cracking becomes more prevalent and hole pull-away/resin recession becomes
less significant?
Lots of questions, but your comments would be most welcome to teach me
about this area of interest.
Best regards
Peter
[log in to unmask] 28/03/2003 11:16 PM
To: DUNCAN Peter/Asst Prin Engr/ST Aero/ST Group@ST Domain, [log in to unmask]
cc:
Subject: Re: [TN] non functional pad removal
Hi Peter,
You are correct. If you plate the barrel on the thin side and the hole
diameter is large, the hole wall will buckle [plastically deform] inwards.
On
cooling this causes 'resin recession' or 'hole-wall pull-away,' and
inner-layer [post] separation on layers near the surface.
Most through-holes nowadays are however small-diameter vias, which are more
susceptible to barrel cracking.
Regards,
Werner
In a message dated 03/27/2003 19:27:43, [log in to unmask] writes:
>I heard stories in my last Company about barrels in holes for PTH
>components being "too small" or " too deformed' to permit components to be
>fitted. Turned out to be a combination of finished hole diameter not
having
>sufficient component lead/solder clearance and barrel-crushing through
>board expansion/contraction. Maybe wrong choice of PCB materials as well,
>I don't know. It was remarked, however, that the effects would have been
>greatly mitigated if n.f. pads had been retained.
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