In a message dated 01/31/99 10:58:01, you wrote:
>-----Original Message-----
>
>From: [log in to unmask] <[log in to unmask]>
>To: [log in to unmask] <[log in to unmask]>
>Date: Saturday, January 30, 1999 11:08 PM
>Subject: Re: Re: Re: [TN] Removal of Lead
>
>Werner: I have absolutely no argument with the statement that other solder
>finishes than HASL'ed solder result in reliable solder joints—I am well
>aware of the studies done by my former colleagues at Bell Labs in Richmond
>with OSP, and other workers with other surface finishes.
>Bob: Greetings, Fellow of BTL: I, too, hail from that institution of
>unlimited R&D funding (at least until I left in 1983, just prior to
>Divestiture). I did circuit design for BTL Whippany and Bedminster (NJ) with
>prototypes running out of the Baltimore Works of WECo (the designs
>subsequently went into production at WECo/Richmond).
>Anyway, I think this conversation of a lead-free PWB has drifted
>back-and-forth from the bare-board level (solder finish) to the final
>assembly level (solder joints) which may explain some of the disagreement. I
>associate "finish" as generally referring to the bare board
>(HASL/OSP/immersion metals) and solder joints as the final assembly.
>Werner: However, the argument started as the total replacement of Sn/Pb
>solder with other solders (or whatever), and my input referred to solder
>joints made of those leadfree solders or conducting epoxies. And for those
>solder joints I stand by my remarks.
>Bob: I personally have little experience with tin/silver solder joints, but
>Werner - I'm certain several large OEM's have been using other lead free
>alloys for decades. Example: IBM has exhaustively studied and subsequently
>used Bi-Pb solder in mass production, according to their reports which date
>back to the late 60's. And in the 70's IBM pioneered this process in
>combination with a solder-free terminal pad (Enthone Entek Cu-56, an early
>predecessor to the current Cu-106A formula). Ditto Texas Instruments Johnson
>City, TN (now Siemens), who under the TI banner was purchasing lead-free
>PWB's back in the early 80's, and then in the mid-80's virtually put
>conductive inks on the map (through independent testing with AMP using the
>UL standards of that time).
>While I admit a Public Domain standard does not yet exist for many of the
>alternatives, it has been my experience that the Public Domain is always in
>the position of catching-up to what the leaders in our industry have already
>championed. Catching-up is NOT a position in which my clients wish to dwell.
>And as for my remarks, I'll stand by the historical record.
>Bob Lazzara
Hi Bob,
As usual, things are more complicated than can be put in short e-mail
messages. Reliability—and what it means and doesn't mean—has to be put into
perspective.
The solder material is in the total reliability scheme a second-order
(affecting reliability by orders of 2 to 3X) variable. More important first-
order parameters affecting reliability in the order of 10X are component size,
delta-CTE, delta-T, solder joint height, lead stiffness.
As a consequence, other solders may be a factor of 2 to 3 less (or more)
reliable than Sn/Pb solders, which in many applications would never show up
because of benign use environments or other load reducing parameters. Further,
solder joint failures have a rather wide statistical distribution which with
an insufficient number of samples and less than impeccable testing techniques
makes order of 2X differences disappear in the noise. To rely on field data
and anectodal industry experience is very dangerous unless you know all the
details; I still recall the essentially impossible task of getting properly
documented field failure data to make any sense out of when at Bell Labs. I
worked 24 years at Bell Labs Whippany in the Interconnection Reliability Lab
and got out in early 1990 when the going was good. If it coundn't be done at
Bell Labs, I doubt it was possible elsewhere; my consulting experiences over
the years certainly have reinforced that opinion.
Werner Engelmaier
Engelmaier Associates, L.C.
Electronic Packaging, Interconnection and Reliability Consulting
7 Jasmine Run
Ormond Beach, FL 32174 USA
Phone: 904-437-8747, Fax: 904-437-8737
E-mail: [log in to unmask]
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