Richard Ackerson asked:
>I am looking for feedback in regards to a question of SMT acceptance in
>various industries.
>
>We are in the Industrial Controls Industries, suppling Process
>Industries in Petro Chemical, Food, Pharmacuticals, and Power
>Generation. Our newer products are being designed utilizing surface
>mount technology. We are also redesigning older products using SMT.
>
>Some of our customers are questioning the reliability of SMT versus
>Throug-Hole for thier credical applications. They are looking for
>definitive answers.
Definitive? You will have to furnish test data on the actual design to
accomplish that. Thermal shock, vibration, etc.
>How would you answer their concerns?
If you are being told that you must continue to use only through hole
components on circuit boards of any complexity to avoid the concern, these
customers have been kept in the dark too long. Consumer products, telecomm,
medical, aerospace, etc. have all been using SMT PCB's for years. There is
no inherent reduction in reliablity due to the use of SMT components. The
interface of a modern SMT IC to the board is _more_ reliable than the DIP
to PTH mounting used 10-15 years ago.
>Please provide input regarding the industry you service, including
>military, andthe length of time SMT has been utilized.
Perhaps you will get cooperation from others. From my perspective, it
almost seems a silly question to ask; but I will say that SMT has been used
in personal computers, followed a few years later in telecomm multiplexers,
line cards, and channel banks; now even avionics - all beginning in the
early to mid 80's. By the early 90's SMT was the dominant mode of
assembling digital electronics at the board or module level for almost any
type of electronics on the market. Check your consumer items - portable
radio transceivers, cellular phones, automotive controls and the list is
endless. It would be much more difficult to find common expamples of any
modern electronics which _don't_ use SMT. None come to my mind quickly. By
the late 90's (here we are...) SMT has become the NORM.
If you are interested primarily in "high power" components, it may be true
that extreme power dissipation devices continue to appear with through hole
mounting. This permits the lead to be longer and separate the solder joint
from the body of the part which generates heat. SMT parts have active
elements within small fractions of an inch of the device solder joint. Even
the concern of the melted joint can be addressed with high temperature
solder and higher performance laminates.
I have little experience with such high power components, but can tell you
that common analog designs like switching power supplies (which have
considerable numbers of resistive devices) have been using SMT board
modules for at least 10 years.
The concerns will have to be addressed by intelligent designs and by
testing. I would only add that if you are mandated to stay with "through
hole only", in a few years you may as well go back to tubes and discrete
parts. There are those who insist on them as well.
regards, (apologies if this sounds offensive)
Jerry Cupples
Interphase Corporation
Dallas, TX USA
http://www.iphase.com
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