30 Jul
2000
30 Jul
'00
10:20 p.m.
There's also the weird secondary market that
exists because of military
programs. TI has previously sold the IP and remaining dies for end-of-life
parts to other firms who then either continue production or package the
dies to meet military needs -- which is great if you need something in
a flat-pac...
Whatever happened to the flat-pac? It seems to me to be a package that
has many of the same advantages of modern SOIC's, but maybe 30 years ahead
of its time. Was it a manufacturability issue? Was it a "proprietary"
issue? The flat-pacs I worked with were ceramic or ceramic/gold, but it
seemed pretty straightforward to me to do the same thing with plastic. Am
I wrong?
Besides, many of the flat-pac pinouts were different than the DIP pinouts,
and this was actually a good thing in the case of many TTL IC's which had
power and ground pins in weird places... It seems to me that in most
cases SOIC IC's follow the DIP pinout (though I'm sure there are exceptions.)
Tim.
31 Jul
31 Jul
10:27 a.m.
CLASSICCMP(a)trailing-edge.com wrote:
Whatever happened to the flat-pac? It seems to me to
be a package that
has many of the same advantages of modern SOIC's, but maybe 30 years ahead
of its time. Was it a manufacturability issue? Was it a "proprietary"
issue? The flat-pacs I worked with were ceramic or ceramic/gold, but it
seemed pretty straightforward to me to do the same thing with plastic. Am
I wrong?
I don't know. They were clearly harder to handle than DIPs, and in
a weird twist they were actually harder to use than DIPs in some military
applications where the enclosure had to be sealed in order to meet
corrosion, fungus or altitude MilSpecs. In such cases the common
approach was to straddle thermal frames with DIPs and use the thermal
frame to conduct the heat to the sides of the enclosure and then design
the enclosure itself to get rid of the heat. The ME types always told
me that this was easier to do with DIPs than with flat-packs, but I
was never clear why a frame bolted on top of a flat-pack was inferior
to a DIP straddling the frame. There was also an assertion that
for this reason flat-packs were generally used in short-life
applications, such as seeker or guidance electronics, but I have
no evidence to suggest that this was anything more than legend.
--
Chris Kennedy
chris(a)mainecoon.com
http://www.mainecoon.com
PGP fingerprint: 4E99 10B6 7253 B048 6685 6CBC 55E1 20A3 108D AB97
1:07 p.m.
I don't know. They were clearly harder to handle
than DIPs,
That is exactly it. I don't think flatpacks ever could be pick-n-placed
effectively. Soldering may have also been a problem, with the long leads.
Every picture I have seen of a flatpack line in a factory involves hand
placed parts soldered with little irons.
SOICs are clearly the winner in the space department as well. The
flatpack thinking had each lead only slightly "gull winged", and rather
long. With SOICs, the lead in preformed and small - great for automation
and space savings.
In such cases the common
approach was to straddle thermal frames with DIPs and use the thermal
frame to conduct the heat to the sides of the enclosure and then design
the enclosure itself to get rid of the heat. The ME types always told
me that this was easier to do with DIPs than with flat-packs, but I
was never clear why a frame bolted on top of a flat-pack was inferior
to a DIP straddling the frame.
The thermal resistance of ceramic DIPs is less than flatpacks. The result
is better heat flow to the frames.
There was also an assertion that
for this reason flat-packs were generally used in short-life
applications, such as seeker or guidance electronics, but I have
no evidence to suggest that this was anything more than legend.
Maybe, I had not heard that one. Possible reasons may be weight, size, or
the fragility of flatpacks.
One thing that I have seen is that really very little military
electronics does use flatpacks - most stuff is made of lots of cerDIPs
(heavy boards!).
William Donzelli
aw288(a)osfn.org
8692
days inactive
8692
days old
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aw288＠osfn.org -
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CLASSICCMP＠trailing-edge.com