Early this month we had a customer audit. One of the findings regards the environment measurements in our assembly area. They noted that we only have one temperature/humidity logger and it was considered inadequate given the size of our production floor.
Isn't one temp/humidity logger per facility adequate? If we add additional temp/humidity loggers, where should we place them? Near machines, near the center of production area, in the four corners?
M.R.
Experts Comments
Wouldn't it make sense to put temp/humidity monitors
in critical locations, such as board and component storage areas, near the
solder paste stencil printer, near the functional and in circuit test areas,
and any where assemblies are staged that would sit for more than a few
hours.
Terry Munson President/Senior Technical Consultant Foresite Mr. Munson, President and Founder of Foresite, has extensive electronics industry experience applying Ion Chromatography analytical techniques to a wide spectrum of manufacturing applications.
Temperature and humidity can effect ESD, MSD, screen
printing, working time, and shelf life. If you don't measure / monitor
all the multiple areas, you'll never be able to prove you don't need to.
Mark Waterman Engineer / Trainer Electronic Controls Design, Inc. (ECD) Mark Waterman is a trainer and field engineer with 17 years experience in service and applications specialties. Intimate knowledge of soldering processes and measurement systems. Six sigma and statistical process control generalist.
Whether
one logger is enough is entirely dependent on the facility. In facilities where
airflow into/out of the facility is tightly controlled, and the facility is
under slight "positive pressure" with more make-up air than exhaust, one logger
might in fact be enough. In many facilities, especially older ones, we
don't have this luxury. How many loggers we need, and where we place them will
depend on a number of variables.
Some of these are:
How much heat and/or humidity is produced by processes on the
production floor, and where
How the make-up air and exhaust are configured
Where the main "leaks" are that allow exchange of air with
uncontrolled environments, and how big the leaks are
The capability of the HVAC system in use
My
preference is for wireless digital loggers that transmit data to a central
system for storage. The data can then be tracked and analyzed. Start with a
two-logger system, with the main logger located near your most critical process
(ours is near the SMT assembly area). Move the second logger around to spots that
you suspect may incur variation; monitor each spot through a few weeks' time,
then move to the next spot.
Correlate your temperature and humidity data with
the outside temperature and dew point. The outside dew point is an incredibly
important factor, and is the one variable that drives out-of-control conditions
on the shop floor more often than any other, in my experience.
Once you know where your "sensitive spots" are, you can add loggers to
keep track of them. On most moderate-sized production floors, I don't see a big
benefit to more than three loggers, in most cases.
Fritz Byle Process Engineer Astronautics Fritz's career in electronics manufacturing has included diverse engineering roles including PWB fabrication, thick film print & fire, SMT and wave/selective solder process engineering, and electronics materials development and marketing. Fritz's educational background is in mechanical engineering with an emphasis on materials science. Design of Experiments (DoE) techniques have been an area of independent study. Fritz has published over a dozen papers at various industry conferences.
One should not challenge an auditor, however it would be fair to
ask, what standard indicates that more than one temperature/humidity instrument
is required. IPC standards (J-Std 001) recommend you control the temperature
and humidity, but they do not tell you how.
However, rule of thumb can apply here. One question to ask
yourself: How many HVAC system control thermostats are in the same
area/facility? It would be fair to suggest that you should have the same number
of temperature/humidity measurement instruments in that same area/facility.
Another rule of thumb is one temperature/humidity instrument per 10,000 square
feet of floor space.
As for where to place them, this is simple: where people and product
spend the most amount of time. The whole point of measuring the temperature and
humidity is to document that people and product are NOT being subjected to
extremes. So place instruments where the action is: on the line, in or near the
machines, etc.
Paul Austen Senior Project Engineer Electronic Controls Design Inc Paul been with Electronic Controls Design Inc. (ECD) in Milwaukie, Oregon for over 34 years as a Senior Project Engineer. He has seen and worked with the electronic manufacturing industry from many points of view, including: technician, designer, manufacture, and customer. His focus has been the design and application of thermal process measurement tools used to improve manufacturing processes like: mass reflow and wave soldering, bread baking, paint and powder curing, metal heat treatment and more.
First &
foremost...."your customer audit" They are making the request.
Customers are hard to
come by. Monitors are relatively inexpensive.
You do not indicate the
size of your facility so an accurate answer is difficult.
A monitor at the center
of your facility is ideal but it will not provide accuracy of readings at the
far corner, say near your reflow line or your washing system. Humidity will
generally be different in various areas of your facility
The question itself
raises these questions... are you controlling humidity currently?
Where are you located? A high humidity
area.. Florida? A low humidity area... Arizona?
There are wireless units on the market now that
can mo niter locations & report back to one central PC. THis provides
facility wide reading with automated recording of the factors required.
Jerry Karp President JSK Associates Based in. Northern California since 1971. Founded JSK Associates in 1979. Actively involved in soldering, cleaning, chemistries. 30 years experience in EOS/ESD control.
Humidity
and temperature monitored areas are areas where
these parameters can possibly impact the process yields and or quality.
Some
areas that are normally monitored are:
Solder paste and flux
storage areas
Other chemical storage
areas such as conformal coating and chemistries used in the assembly process
Solder paste printing
areas
The SMT line
Board and component
storage areas
Storage for assemblies
in the process of being finalized, where waiting for a few days may be
required.
Inventory areas for assembled products
Peter Biocca Senior Market Development Engineer Kester Mr. Biocca was a chemist with many years experience in soldering technologies. He presented around the world in matters relating to process optimization and assembly. He was the author of many technical papers delivered globally. Mr. Biocca was a respected mentor in the electronics industry. He passed away in November, 2014.
The
answer is dependent on the uniformity of the temperature and humidity within
the room or on the factory floor. Large areas are subject to variations
in temperature if the air handlers are not positioned properly or correctly
balanced. A common mistake is locating temperature/humidity monitors
within the near draft path of an air conditioner vent. Ideally, before
stationing any temperature/humidity monitors, the room will be mapped
especially for temperature uniformity.
Influences of operating equipment,
the number of people present, outside environment, wind conditions, opening and
closing doors, consistency of air conditioner output, exhaust stack vent motors
on and off, among other factors, can all impart changes to the
environment.
Even after such mapping and impact studies, I always
encourage deployment of multiple recording temperature/humidity monitors; one
in the center and at least a couple at extreme opposite corners or a large room
or factory floor. Frequent and routine monitoring of the
temperature/humidity graphs is a must to understand environmental impact on
materials and ensuing quality.
Gary Freedman President Colab Engineering A thirty year veteran of electronics assembly with major OEMs including Digital Equipment Corp., Compaq and Hewlett-Packard. President of Colab Engineering, LLC; a consulting agency specializing in electronics manufacturing, root-cause analysis and manufacturing improvement. Holder of six U.S. process patents. Authored several sections and chapters on circuit assembly for industry handbooks. Wrote a treatise on laser soldering for Laser Institute of America's LIA Handbook of Laser Materials Processing. Diverse background includes significant stints and contributions in electrochemistry, photovoltaics, silicon crystal growth and laser processing prior to entering the world of PCAs. Member of SMTA. Member of the Technical Journal Committee of the Surface Mount Technology Association.
