Dwight,
Yes and no: we are monitoring the press fit insertion force (we are not
extracting them...) for back planes, not for inserted cards.
Any how, as of the generic question and the reliability thread that was
evolved from: it is true that the callout parameters are important;
however, the reliability of the hole - regardless whether the hole is
for through component or for via - is defined by process parameters:
most of the failures we've experienced came from poor drilling and
connection of the barrel to the layers (failures of the etch back).
Hence, while assessing a PCB making shop, I pay attention to the
drilling design, bits management (count of hits and re-sharpening), as
well as de-smear process control and monitoring (not to neglect other
major processes, of course).
Regards
Ofer Cohen
Manager - Quality Assurance and Reliability
SIEMENS COM FN A SB
-----Original Message-----
From: Dwight Mattix [mailto:[log in to unmask]]
Sent: Wednesday, January 18, 2006 01:35
To: Ofer Cohen; TechNet E-Mail Forum
Subject: RE: [TN] Drill and plated hole callouts
are you also measuring press fit insertion and extraction force (as a
predictor of gas tight joint)?
At 08:37 AM 1/17/2006, Ofer Cohen wrote:
>Dwight,
>I used to send the data as you describe. For the matter effect, the
>parameters were extracted from the connectors' data sheets. However,
>time after time we received from various manufacturers the request to
>give them the final hole diameter and tolerance (+/-2 mils), and the
>minimum copper thickness (25 to 50 micron). Hence, to avoid
>interactions, we changed the callout to the vendors' request. We are
>monitoring the outcome through micro sections.
>
>Regards
>Ofer Cohen
>Manager - Quality Assurance and Reliability
>SIEMENS COM FN A SB
>
>-----Original Message-----
>From: TechNet [mailto:[log in to unmask]] On Behalf Of Dwight Mattix
>Sent: Tuesday, January 17, 2006 17:23
>To: [log in to unmask]
>Subject: Re: [TN] Drill and plated hole callouts
>
>I concur with Werner with the key exception being for press fit
connector
>holes.
>
>Our experience dictates that we specify press fit holes with
>a) manufacturer's exact drill size, (provides the ideal "Goldilocks"
>envelope for the needed copper deformation -- not too much to crack
>copper,
>not too little and not achieve gas tight joint)
>b) minimum copper thickness, (we spec 0.0012" min for older 2.5 mm
pitch
>and 0.001" min for 2.0mm pitch press fit) and
>c) minimum finished hole size (too small will increase insertion forces
>overwhelming the insertion press or causing pins to "Z-kink" onto pwb
>surface).
>
>These factors combine to ensure a reliable gas tight joint without
>excessive insertion forces or excessive hole wall deformation (leading
to
>post separation or barrel cracking).
>
>It all starts with using the proper (precise) drill size. The
connector
>mfg's recommended drill size is the paramount concern.
>Ergo, the exception where drilled hole size should be specified.
>
>my $.02,
>dw
>
>
>At 05:41 PM 1/16/2006, Werner Engelmaier wrote:
> >Hi Bob,
> >The call out of finished hole size is an anachronism left over from
the
> >through-hole technology era. In modern high-density PCBs you should
> >specify the
> >drilled hole size (no tolerance) with a minimum plating thickness in
>the
> >hole to
> >be verified by cross-sectiong of coupons.
> >The reliability of your vias depends on PCB thickness, drilled hole
>size, Cu
> >plating thickness, Cu plating quality (verified by testing co-plated
>mandrel
> >foils for tensile strength and ductiolity--not elongation). Your
friend
>is
> >right,
> >electrical test is not enough. You should have coupons either IST or
> >HATS-tested. This will be even more important with LF-soldering
> >temperatures. You then
> >might want to specify not only Tg, but Td and CTE(z) as well.
> >
> >Regards,
> >Werner Engelmaier
> >Engelmaier Associates, L.C.
> >Electronic Packaging, Interconnection and Reliability Consulting
> >7 Jasmine Run
> >Ormond Beach, FL 32174 USA
> >Phone: 386-437-8747, Fax: 386-437-8737, Cell: 386-316-5904
> >E-mail: [log in to unmask], Website: www.engelmaier.com
> >
> >
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