| Overview: |
Micro-abrasive sand blasting
is accomplished by propelling a finely graded abrasive powder into a
stream of compressed air, through an abrasive-resistant hose and out a
miniature nozzle manually or automatically positioned at the workpiece.
The process is used to remove a variety of conformal coatings, including
epoxy, acrylic, urethane, silicone, parylene, and ultraviolet-cured
materials, from printed circuit boards for rework and repair. It replaces
chemical, mechanical, and thermal methods of coating removal. Some
micro-abrasive units also can be used for other functions, such as
deburring, texturing, drilling, and cutting.
Five functions in micro-abrasive blasting
control the process: 1) air pressure, 2) nozzle diameter, 3) distance
of the nozzle from the workpiece, 4) powder flow rate, and 5) type of
abrasive powder used. A variety of different abrasives can be used
depending on the application. These may include aluminum oxide, silicon
carbide, glass beads, sodium bicarbonate, walnut shell, or plastic media.
Each is used in a microscopic form usually between 10 and 150 microns.
Several of these media may not be appropriate for conformal coating
removal, so it is important to check the specifications and suggested uses
for each before using them.
Units range from compact, manually operated benchtop
units to fully automated programmable equipment. In either system, clean,
dry air is mixed with a precise quantity of abrasive material and
propelled at 75 to 100 psi through an extremely small nozzle at the end of
a pencil-shaped stylus. The abrasive material is directed at a target area
to accomplish a specific task. Spent material is continuously drawn out of
the work chamber via a vacuum and then sent through a filtration area to a
dust collection system. Some systems collect spent media for reuse, thus
reducing overall operating costs of the system.
|
| Compliance
Benefit: |
Micro-abrasive sand blasting
operations generate less hazardous waste than chemical stripping since
solvents are not used. The decrease in hazardous waste helps facilities
meet the requirements of waste reduction under RCRA, 40 CFR 262; the
Pollution Prevention Act (42 USC 13101-13109); and Executive Order (EO)
13148, Greening the Government Through Leadership in Environmental
Management; and may also help facilities reduce their generator status
and lessen the amount of regulations (i.e., recordkeeping, reporting,
inspections, transportation, accumulation time, emergency prevention and
preparedness, emergency response) they are required to comply with under
RCRA, 40 CFR 262. In addition, the decrease in the amount of
solvents on site decreases the possibility that a facility will exceed
reporting thresholds of SARA Title III for solvents (40 CFR 300,
355, 370, and 372). Furthermore, when used as a substitute for chemical
cleaning processes, micro-abrasive sand blasting will likely decrease VOC
emission levels, thereby potentially reducing the need for an air permit
under 40 CFR 70 and 71.
The compliance benefits listed here are only meant to
be used as general guidelines and are not meant to be strictly
interpreted. Actual compliance benefits will vary depending on the factors
involved, e.g., the amount of workload involved.
|
| Materials Compatibility: |
Abrasive materials must be
matched to the job to avoid inadequate results or damage to the
components. For example, aluminum oxide and silicon carbide will blast
through a board in only a few seconds. Sodium bicarbonate and walnut
shells have high electrostatic discharge readings, which will destroy good
components on a board.
|
| Safety and
Health: |
Appropriate personal protection equipment should be worn. Consult your local
industrial health specialist, your local health and safety personnel, and
the appropriate MSDS prior to implementing this technology.
|
| Benefits: |
- Reduces use of chemicals in process.
- Improves efficiency of operations, saving on labor,
materials, handling and disposal of hazardous waste.
- Improves personnel health and safety in the work
environment.
- Reduces labor hours for coating removal.
|
| Disadvantages: |
- Possible circuitry degradation may occur when the
abrasive stream hits the coating and generates electrostatic charges.
- Excess removal of plating from traces and leads can
expose the base metal to possible corrosion.
- Removal of solder mask off the printed circuit
board (PCB) may cause possible changes to the insulation value of the
PCB.
- Incorrect choice of abrasive can lead to damage of
workpiece or wasted abrasive medium and labor.
- Nonuniform particle size can result in clogging the
nozzle.
- If the system is not clean and dry, clumping can
result, thus clogging the nozzle.
|
| Economic
Analysis: |
According to Mr. Carroll
Claterbuctz of NASA, capital costs for all micro-abrasive blast equipment
(blaster unit, dust collector, work chamber, air filter, point ionizer) is
approximately $5,000 to $13,500, depending on options and levels of
electrostatic discharge protection necessary for the job. Check with the
manufacturers listed below for their specifications.
Polyurethane coating is the most common coating
currently in use. Chemical and micro-abrasive methods of coating removal
are the most appropriate methods for this type of coating. This cost
analysis compares the use of chemical and micro-abrasive methods of
coating removal.
Assumptions:
- Labor costs = $45/hour.
- Cost of blasting material = $120/15 lbs.
($8/lb.)
- Cost of solvent/chemical = $10/gallon.
- Time to remove polyurethane coating from one 1"x1"
component using blast system = 2 minutes.
- Time to remove polyurethane coating from one 1"x1"
component using chemical method = 2 hours.
- Blast equipment uses up to 50 grams of blast
medium/minute.
- Solvent use = 0.125 gallons per job.
- Hazardous waste/solvent disposal = $2/lb.
- One gallon of hazardous waste/solvent = 8
lbs.
- Spent blasting media is assumed to be disposed as
hazardous.
- 1,500 components are cleaned annually.
Removal of Polyurethane Coating from
Printed Circuit Boards Traditional Chemical Removal vs. Micro-Abrasive
Blast System
| |
Traditional Chemical Removal |
Micro-Abrasive Blast System |
| Capital
Costs: |
$0 |
$8,500 |
| Material
Costs: |
$1,875/yr
(solvent) |
$2,670/yr (blast
material) |
| Labor
Costs: |
|
|
| Removal: |
$135,000 |
$2,247.75 |
| Handling: |
$1,124.55 |
$1,124.55 |
| Cleaning: |
$3,373.65 |
$562.27 |
| Waste
Disposal: |
$12,000 |
$661 |
| Total: |
$153,373.20 |
$7,265.57 |
Economic Analysis Summary:
Most of this
savings is realized in reduced labor costs and reduced hazardous waste
disposal costs. These figures do not factor in worker safety improvements
associated with micro-abrasive blast systems. In addition, the material
costs for micro-abrasive systems would be less if the spent blast material
were reused. Also, the plastic media that is most often reused does not
leave a residue on a printed circuit board, and therefore, eliminates the
need for and the cost of cleaning. All of these factors would decrease the
overall cost of a micro-abrasive blasting system.
- Annual Savings for Using Micro Blast System:
$146,108
- Capital Cost for Diversion Equipment/Process:
$8,500
- Payback Period for Investment in Equipment: 1 month
Click
here to View an Active Spreadsheet for this Economic Analysis and
Enter Your Own Values. To return from the Active Spreadsheet, click the
Back arrow in the Tool Bar
|
| NSN/MSDS:
|
None identified.
|
| Approving Authority: |
Appropriate authority for making process changes should always be sought and obtained prior to procuring or implementing any of the technology identified herein.
|
| Points of Contact: |
For more information
|
| Vendors: |
This is not meant to be a complete list, as there may be
other suppliers of this type of equipment.
Conformal Coating Removal Co.
3815 South
Main
Santa Ana, CA 92707
Phone: (714)
513-1503
FAX: (714) 513-1510
Comco, Inc.
2151 N.
Lincoln St.
Burbank, CA 91504
Phone: (800)
796-6626 or (818) 841-5500
FAX: (818)
955-8365
Crystal Mark,
Inc.
613 Justin Ave.
Glendale, CA
91201-2396
Phone: (800) 659-7926 or (818) 240-7520
FAX:
(818) 247-3574
Contact: Ms. Rhonda Friga
Email: rhonda@crystalmark.inc.com
|
| Sources: |
Mr. Hal Horrocks, Conformal
Coating Removal Techniques, President of CCRCo., presentation for NEPCON
West 1997.
Personal communication with Mr. Don Larson, McClellan Air
Force Base, CA, April 1997.
Personal communication with Mr. Carroll
Clatterbuctz, National Aeronautics and Space Administration, Goddard Space
Flight Center, MD, August 1998.
|
| Supplemental: |
Picture of Precision Micro-Abrasive Sand Blasting For Cleaning Circuit Boards
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