Mornin' Steve and All -
Well, how do I start this? Once upon a time, in days of yore .....
The ceramic quad flat pack was preceded by the flatpack which came on our
horizon in the horizon in the late 60's. At the time, none of us envisioned
industry wide standardized pad patterns and form factors, nor the level of
automated placement equipment we have today. (The old USM transfer line was
the miracle of the modern age and the Hollis SD-7 was about the hottest wave
solder going.) The flat pack was supplied in a generally flat condition and
used in three primary ways: with the leads flat out in welded cordwood
modules; with the leads joggle formed and soldered to a circuit board; or
with the leads bent at right angles and inserted in thru holes for wave
soldering. All of us tooled up for our own design needs and marched on with
life. Looking back, none of this was particularly pleasant or easy, but it
was the norm for that period.
Somewhere along in the mid to late 70's I ran into my first ceramic quad
flatpacks (CQFP) as a part of an RF design. These little fellows had
several other colloquial names, not printable in this forum. By the mid
80's and later, there was a considerable proliferation of CQFP's in all
sizes, a variety of case styles, and once again, virtually none of us had
gone to standard form factors or standard pad sizes that extended beyond our
own corporate boundaries. In general, these parts were not the high volume
runners that exist as plastic QFP's. Once upon a time, we had an Adept
robot with dual vision, all tooled up to pick, scan and place flat packs and
CQFP's. (Many of the CQFP's were running $2K-$4K a pop, so placement speed
was not a primary issue.)
In defense of the components industry (which I rarely do), they gave those
of us in the design and assembly part of the world what we thought we wanted
at that time. The CQFP just sort of grandfathered into the flatpacks shoes,
at the time.
The only improvement I've seen in CQFP's in many years is the advent of the
top brazed lead frame, which gets away from the old nickle/iron lead frame
that was fused in the frit. That old lead frame material added a lot of
solderability variables that kept most of us pulling our hair out most of
the time, not to mention variations in springback after forming.
Lead finishes on the current families of CQFP's generally originate with the
case fabricator (Kyocera, or whoever) rather than the CQFP assembler, gold
being the only finish available in most cases. I have seen the result of IC
assemblers trying to pretin these fine pitch devices, and believe me you
don't really want any of that.
There are several contract services out in the world that will form and tin
the CQFP's, I can think of Tintronics, here in our local area. This can get
a bit pricey because of form & tin tooling, then there's the issue of
carriers to get the parts back to you, unmutilated.
So far as form tools, I've had good success with die sets from Fancort,
Knight Tool and a couple of others. Once again, they're on the pricey side.
Sorry this doesn't provide any nice clean answers or innovative solutions.
Regards - Kelly
-----Original Message-----
From: Stephen R. Gregory <[log in to unmask]>
To: [log in to unmask] <[log in to unmask]>
Date: Monday, May 01, 2000 9:20 PM
Subject: [TN] Manufacturability issues with components...
>Hi ya'll...
>
>I guess I'm on a roll now...just want to vent about manufacturability
issues
>with SMT components. I've been exposed to issues at my present position
with
>certain devices that create nightmares when trying to build the assemblies.
>This is aside from the issue that I have with the BGA device I've been
>posting about, there's more...
>
>There's an assembly that we build here that has two 352-pin ceramic 20-mil
>pitch, gold plated leads, QFP's that only comes in a carrier that has to be
>pre-tinned, cut and formed, prior to placement and reflow. We do the
>pre-tinning and cut and form ourselves in-house with a Mannix press and
>adjustable die. You can imagine what fun that is...
>
>My question is (and I'm pretty sure I won't get a good answer) why in
heaven
>do the component vendors supply the parts only this way?
>
>I've checked with them and the configuration that the components are
>supplied, is the only way they come...they won't pre-tin and form them.
I'll
>just leave it up to your imagination who the supplier is....
>
>WHY? OH WHY? Obvoiusly the parts are meant to be surface mounted, why not
cut
>and form them into a standard foot-print? The issues with gold
embrittlement
>are old as dirt, why do they still supply parts this way?
>
>Further still, why do I have to do it? I wouldn't mind paying more for
>pre-tinned and formed parts either! HONEST!!!
>
>If any of you have had the pleasure of pre-tinning, and then cut and
forming
>20-mil pitch QFP's, you know my agony...
>
>If there is anybody from the component vendor arena reading the list, I
would
>like to understand your views on the issues...
>
>Sorry if I seem to be beating-up on the component vendors today...but I've
>been having nightmares lately about this stuff...
>
>-Steve Gregory-
>
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