Usos Del Stencil
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Transcript of Usos Del Stencil
8/14/2019 Usos Del Stencil
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SparkFun Electronics Stenciling
Materials by Bob Hunke & Linz Craig
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Why Stencil?
• Smaller footprint means smaller board
• Tight pitch components
• Multiple boards at a time
• Greater efficiency
• “Hidden” connections
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Materials Needed
• Stencil
• Paste
• Reflow capability
(oven, hot plate, iron)
• Stencil frame
• Squeegees/putty knife
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Plastic vs. Metal Stencils
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Plastic vs. Metal Stencils
Cost• The metal stencils SFE gets are laser
etched & sold by the 15” x 15” sheet at
$125
• Plastic stencils are $25 plus shipping per
board
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Plastic vs. Metal Stencils
Ease of Use• Make sure that your stencil extends over
the end of your frame or framing scrap
PCBs
• Stiffer stencils are easier to pick up off of
the board, hence metal is easier to workwith
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Plastic vs. Metal Stencils
DIY• Cut your own plastic stencils fairly easily
• Chemically etch your own metal stencils
not so easily• Machine cut your own stencil if you’ve got
the hardware and software (this is
becoming more and more common)
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Plastic vs. Metal Stencils
Quality of work
• Metal stencils tend to make for betterpaste placement
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Paste Types
• Leaded vs. Lead free
• Flux: Clean vs. no clean
• Size: SFE uses Type 3, average soldersphere of 36 microns
• Five-ball rule for choosing type:
Smallest component footprint should be nosmaller than five times the width of average
solder sphere
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Type 3 Paste Cost
• SFE, leaded: $9.95 for 50g
SFE, leaded Lead free, $63 Syringe style
• Larger quantites: 500g $100 - $150
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Paste Storage and Handling
• Store your paste ina cool place such
as a refrigerator• For short term
storage room
temperature isokay
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Applicators: Squeegees
• Professional,designed
specifically forpaste, machineready
•
Possible tochange blade
• Expensive($35 - $350)
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Applicators: Putty Knives
• Inexpensive($1 - $20)
• Sharp edge (maydamage stencil)
• More flex than
Squeegees
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Safety Concerns
• Sharp edges
• Lead, tin, silver,copper
• Eye irritant• Extreme temps
(re-flow)
• Fiberglass shards
• Occupational hazards(Paster ’s Elbow)
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Setup
• Frame your PCB
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Setup
• Apply paste to your applicator evenly
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Setup
• Align yourstencil
• Apply steadypressure onone side
• Make surethe surfaceis flat & even
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Apply the Paste
Proper grip 15 – 45 degrees Even
distribution
Cleanup 60 - 80 degrees Hold & lift off
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Populating
• Tweezers and steady hands
• Placement diagram (build sheet) to makesure everything goes onto the right spot
• Careful with polarized components
• Start with lower profile components first
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Populating
• Small margin of error (surface tension)
• Don’t smear the paste
• Nudge with tweezers, don’t push down
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Reflow: Professional re-flow oven
• Big and costs a lot ($1500 used on ebayto $50,000 and up)
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Reflow: Desktop re-flow unit
• Small unit, IC controlled cooking
• Mid range price ($250 to $800)
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Reflow: Hot plate
• May yellow silk screen
• May cook unevenly
• You have to time it yourself
• Cheap ($40)
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Reflow: Soldering Iron
• Can be difficult to reach components
• Useful for rework and PTH
• Price ranges ($10 - $200)
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Reflow
• Heat sinks, PTH and heat sensitivecomponents should be added after re-flow
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Paste Cleanup
• Paste isn’t cheap, save paste by scrapingit back into your container
• Clean off your stencil and tools with wateror isopropyl alcohol
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Creating a PCB and Stencil
Layout Software• Eagle: www.cadsoftusa.com
Free trial download available, robust, what SFE uses
• KiCad EDA: www.kicad.sourceforge.net
Free opensource schematic & PCB layout software
• Fritzing: www.fritzing.org
Free educational virtual prototyping tool, only one
layer of traces available, great for beginners
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Creating a PCB and Stencil
Gerber File Formats• .GTP (top paste –aka stencil file)
• .GTO (top overlay –aka white ink)
• .GTS (top soldermask)• .GTL (top layer –aka actual copper)
• .GBL (bottom layer –aka actual copper)
• .GBO (bottom overlay –aka white ink)• .GBS (bottom soldermask)
• .TXT (drill –aka any holes in the board)
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Creating a PCB and Stencil
or Make Your Own• Ferric Chloride etching:http://www.instructables.com/id/Making-stencils-for-solder-paste-at-home/
• Laser Cutting:http://www.zblob.com/solder_paste_stencil.html
• Milling:
http://www.millpcbs.com/phpbb3/viewtopic.php?f=12&t=36
• Photo etching is also a possibility
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More Info
• Stencil manufacturers:
Ohararp.com, Soldermask.com, Pololu.com
• Paste manufacturers:
Techni-tool.com, Kester.com, Zeph.com
• Squeegee manufacturers:
Ntscope.com
• PCB manufacturers:BatchPCB, Gold Phoenix, Advanced Circuits, PCBUniverse
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Questions?
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www.sparkfun.com
6175 Longbow Drive, Suite 200
Boulder, Colorado 80301