Rick,
Since the size of spacing and component lead pitch are reduced by industry
needs, many new devices and designs cannot perform adequately in humid life
cycle environments without some form of protection to the conductors.
Many manufacturer's are being required to apply conformal coatings to
electronic assemblies to enhance reliability.
You actually have many conformal coating options.
Silicones are generally used for automotive type applications where the
circuit boards are going to see extreme temperature cycling environments.
They are soft elastomeric materials with limited abrasion resistance.
On the other hand, the organic family of conformal coatings encompass AR
(acrylic resin), ER (epoxy resin), and UR (urethane resin), materials
including the UV hybrids like AR/UR, and are "general purpose", tough, high
dielectric materials.
Many of these materials have been formulated without solvents so high VOC
issues and solvent dilution are no longer a factor in production. They also
coexist very well with various solder masks and soldering flux residues.
Loctite does not get involved with solvent based coating chemistries. All
my stuff is solvent free.
Curing option include UV with secondary ambient moisture for shadowed areas
and heat cures. The UV's are the most efficient for high volume short cycle
time applications such as 5293 silicone and 394 ARUR.
As far as equipment suppliers, you have 3 of the largest players home based
right here in the US.
1. Nordson Corporation, Amherst, OH (440) 988-9411, produce in-line
selective coating systems for UV and heat cure materials. The most recent
development is their "SwirlCoat" dispense head which allows the user three
different dispense patterns within the same dispense head / program. They
employ there own non-atomized dispense head technology. Nordson is the
leader in high volume production systems.
2. Precision Valve and Automation, Halfmoon, NY (518) 371-2684 is a
producer of a "very flexible" in-line selective platform which has multiple
heads for a variety of dispense applications for conformal coating. They
employ there own valve technology which is top of the line. They also
provide UV and heat cure tunnels at a fair cost.
3. Specialty Coating Systems, Indy, IN (317) 240-2073 produce an in-line
atomized selective spray platform as well as UV and heat cure tunnels.
They also produce non-selective reciprocating platforms and some dip
systems.
If you chose other than a selective process, you have to contend with
masking and demasking operations which are off line and labor intensive. A
decent "nothing fancy" selective robot and cure cell will run you no less
than $100K.
If you cannot justify a system, you can revert to a standard paint spray
booth and a turn table but this type of efficiency will depend on your
volume requirements.
I would also refer you to the Loctite home page at:
www.loctite.com
steps:
1. chose "United States",
2. then click "electronic products"
3. and then "conformal coatings".
There is a great deal of information including technical articles on
silicones and some on incorporating solvent free conformal coating
chemistries into today's production environments.
You can also refer to the NEPCON West proceeding for the past 6 years.
Several technical papers have been published on these topics.
I travel a lot, but you can also contact me directly if you wish.
Good Luck,
Barry Ritchie
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