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September 1998

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Subject:
From:
Jerry Cupples <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Mon, 28 Sep 1998 11:29:31 -0500
Content-Type:
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Tony Smythe said:

>Hi from NZ. I run a small Prototype Design office and have been designing
>THT boards for small firms for many years. Recently some customers are
>looking to update their designs. Is there any performance or monetary gains
>to be had by changing to mostly SMT? Is there any future in THT? Circuits
>are mostly digital and audio with some RF. Productions runs range from 100
>TO 500. Has anyone made or know of any comparative costs study that can be
>attached to an email please? This has got to be the most boring subject on
>TN but any advice or figures would be very welcome.

Boredom is all relative.

Generally, there is a cost savings associated with SMT components.

IMO, the through-hole packages will continue a long and slow decline, and
in some cases (for example, low voltage digital logic) the availability of
newer technologies in THT will be non-existent. So a designer who wishes to
use the latest logic families will have little choice but to go SMT.

Based on observations here in the US, the older TTL and HCMOS logic
families still being offered in THT packages are comparatively more costly
than equivalent SMT parts. They have less mold compound, smaller
leadframes, and probably smaller die sizes internally, thus they cost more
to manufacture at the device fabrication level. Since they sell more
slowly, you may expect to see higher markups.

The device footprints of even 0.050" pitch SMT parts compared to 0.100"
pitch THT parts is obvious. For boards with say 20-30 active components,
where density of the part placement and routing has been optimized, the
board size may be reduced, and a savings gained.

It is doubtlessly true that power devices, connectors, and an assortment of
parts will probably be offered in through-hole for decades.

Generally, in the US, we see large OEM operations and contract assembly
service providers who cannot keep the old VCD and DIP automation busy
anymore, and they place the parts by hand where present designs still
require their use.

If you are trying to convince yourself that there is no need to move on to
more advance SMT packaging in digital electronics, this is a fool's errand.
My suggestion is that you take some customer's existing design, get on the
web (try http://www.scruznet.com/~gcreager/brief.htm) or send out quotes
for every part on the board which can be converted to SMT. Check the
materials prices, these are the main cost drivers. Your local component
distributor may be able to help.

There was an extensive thread on this subject here last December. See:
http://jefry.ipc.org/SCRIPTS/WA.EXE?A1=ind9712&L=technet#180



regards,





Jerry Cupples
Interphase Corporation
Dallas, TX USA
http://www.iphase.com

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