Strengths and Weaknesses of Current Stencil Technologies · Step Stencil Technology -This paper and...
Transcript of Strengths and Weaknesses of Current Stencil Technologies · Step Stencil Technology -This paper and...
Strengths and Weaknesses of Current Stencil Technologies
Greg Smith
BlueRing Stencils
Outline• Introduction
• Types of SMT Stencil Technology
• Manufacturing Methods
• Stencil Foil Materials
• Step Technologies
• Nano-Coating Technologies
• Conclusions
Introduction
Brief History of SMT Stencil Manufacturing Methods1980’s thru Late 1990’s: Chemically Etched Stencils, Electroformed Stencils
Late 1990’s thru Early 2000’s: YAG Lasers become the new Normal for laser cutting,
Electroformed Stencils
Introduction
Brief History of SMT Stencil Manufacturing Methods2010’s Until Current: Fiber Laser Cut Stencils, Electroformed Stencils.
Electroformed Stencils
Manufacturing Methods
Laser Cut StencilsMost Manufacturers are utilizing Fiber Laser Technology for todays SMT Stencils
Manufacturing Methods
Electroformed StencilsThin foil printing, Ultra Fine Component Printing, High Aperture Count Printing Applications
IMAGED MANDREL
• PHOTO RESIST IS APPLIED TO A MANDREL• PHOTO PLOT IS IMAGED INTO RESIST• UNEXPOSED RESIST IS DEVELOPED AWAY
Manufacturing Methods
Electroformed StencilsThin foil printing, Ultra Fine Component Printing, High Aperture Count Printing Applications
PLATING NICKEL ALLOY
• NICKEL ALLOY IS PLATED ONTO MANDREL TO REQUIRED THICKNESS
Manufacturing Methods
Electroformed StencilsThin foil printing, Ultra Fine Component Printing, High Aperture Count Printing Applications
FINAL STENCIL FOIL
• NICKEL STENCIL IS SEPARATED FROM MANDREL AND MOUNTED TO FRAME
Manufacturing Methods
Electroformed Stencils
Electroformed stencils are 100% nickel with superior paste release characteristics
Electroformed SEM
Manufacturing Methods
COMPARISON (STRENGTHS & WEAKNESSES) OF MANUFACTURING METHODS
METHOD FOIL THICKNESS APERTURE SIZE TOLERANCE
POSITIONAL ACCURACY METAL THICKNESS
FIBER LASER CUT 2 – 10 MIL,SPECIFIC THICKNESS ONLY
+/- 0.3 MILS 0.4 MILS MAX OVER 31.5 MILS STAINLESS +/- 2% OF FOIL THICKNESS
ELECTROFORMED 1-6 MIL7-8 MIL
+/- 0.3 MILS+/- 0.5 MILS
< 10” X 10” WITHIN 1 MIL> 10” X 10” < 16” X 16” WITHIN 1.5 MILS> 16” X 16” < 20” X 20” WITHIN 2 MILS
+/- 5%
*Tolerances presented are based on presenters data
STENCIL FOIL MATERIALS
IN SMT STENCIL PRINTING, ESPECIALLY LOW AREA RATIO PRINTING….FOIL MATTERS!
Impact of Stencil Foil Type on Solder Paste Transfer Efficiency for Laser Cut SMT Stencils - Originally published in the Proceedings of SMTA International, Rosemont, IL, Sept. 17 – 21, 2017
Material “FG” Description Grain Size Category
1 Yes Stainless A
2 No Stainless B
3 N/A Ni N/A
4 N/A Ni N/A
5 No Stainless C
6 Yes Stainless A
7 Yes Stainless A
Grain Size “A”: 1-5 MicronsGrain Size “B”: 6-10 MicronsGrain Size “C”: >10 MicronsNickel Grain Size: Unknown
STENCIL FOIL MATERIALS
IN SMT STENCIL PRINTING, ESPECIALLY LOW AREA RATIO PRINTING….FOIL MATTERS!
Test Vehicle:• 7 Area Ratio Apertures• 5 Mil (125mm) Foil• All square with rounded
corner• 100 Apertures per group
Impact of Stencil Foil Type on Solder Paste Transfer Efficiency for Laser Cut SMT Stencils - Originally published in the Proceedings of SMTA International, Rosemont, IL, Sept. 17 – 21, 2017
STENCIL FOIL MATERIALS
IN SMT STENCIL PRINTING, ESPECIALLY LOW AREA RATIO PRINTING….FOIL MATTERS!
Impact of Stencil Foil Type on Solder Paste Transfer Efficiency for Laser Cut SMT Stencils - Originally published in the Proceedings of SMTA International, Rosemont, IL, Sept. 17 – 21, 2017
Test Vehicle:• 2 Patterns Per Stencil• 1 Pattern Coated with
Ceramic Nano-Coating• 2 Coupons Per Stencil• Cut Same Day/Same
Laser
Coupon
STENCIL FOIL MATERIALS
IN SMT STENCIL PRINTING, ESPECIALLY LOW AREA RATIO PRINTING….FOIL MATTERS!
Transfer Efficiency for Coated and Uncoated Stencils for All Metals with 0.3, 0.4, and 0.5 Area Ratios (Small Area Ratios) Combined.
Impact of Stencil Foil Type on Solder Paste Transfer Efficiency for Laser Cut SMT Stencils - Originally published in the Proceedings of SMTA International, Rosemont, IL, Sept. 17 – 21, 2017
STENCIL FOIL MATERIALS
IN SMT STENCIL PRINTING, ESPECIALLY LOW AREA RATIO PRINTING….FOIL MATTERS!
Impact of Stencil Foil Type on Solder Paste Transfer Efficiency for Laser Cut SMT Stencils - Originally published in the Proceedings of SMTA International, Rosemont, IL, Sept. 17 – 21, 2017
Transfer Efficiency by Metal by Grain Size for 0.4, 0.5 Area Ratios (Small Area Ratio Printing).
STENCIL FOIL MATERIALS
IN SMT STENCIL PRINTING, ESPECIALLY LOW AREA RATIO PRINTING….FOIL MATTERS!
Impact of Stencil Foil Type on Solder Paste Transfer Efficiency for Laser Cut SMT Stencils - Originally published in the Proceedings of SMTA International, Rosemont, IL, Sept. 17 – 21, 2017
Coefficient of Variation by Metal Type.
STENCIL FOIL MATERIALS
IN SMT STENCIL PRINTING, ESPECIALLY LOW AREA RATIO PRINTING….FOIL MATTERS!
Impact of Stencil Foil Type on Solder Paste Transfer Efficiency for Laser Cut SMT Stencils - Originally published in the Proceedings of SMTA International, Rosemont, IL, Sept. 17 – 21, 2017
SEM of Uncoated Aperture Sidewall, Material 1Best Performer, FG Material
STENCIL FOIL MATERIALS
IN SMT STENCIL PRINTING, ESPECIALLY LOW AREA RATIO PRINTING….FOIL MATTERS!
Impact of Stencil Foil Type on Solder Paste Transfer Efficiency for Laser Cut SMT Stencils - Originally published in the Proceedings of SMTA International, Rosemont, IL, Sept. 17 – 21, 2017
SEM of Uncoated Aperture Sidewall, Material 3
STENCIL FOIL MATERIALS
IN SMT STENCIL PRINTING, ESPECIALLY LOW AREA RATIO PRINTING….FOIL MATTERS!
Impact of Stencil Foil Type on Solder Paste Transfer Efficiency for Laser Cut SMT Stencils - Originally published in the Proceedings of SMTA International, Rosemont, IL, Sept. 17 – 21, 2017
CONCLUSIONS• Not all Fine Grain (FG) materials perform the same• Material 1 (FG) and Material 2 (Not FG) were determined to
outperform the other 5 materials when comparing Transfer Efficiency and Coeficient of Variation
• Laser cutting the material with the highest transfer efficiency and the lowest coefficient of variation and applying a Ceramic Nano-Coating produces the best printing process
• SEM Analysis shows that base materials cut differently and some materials exhibit smoother sidewalls than others.
STEP TECHNOLOGIES
Step Stencil Technology - This paper and presentation was first presented at the 2017 IPC Apex Expo Technical Conference and published in the 2017 Technical Conference Proceedings.
Step Down Stencils:
Material thickness is
reduced in areas where
smaller components are
placed on the PWB so that
proper Area Ratios are
maintained to obtain good
paste release.*Step Down Stencil
STEP TECHNOLOGIES
Step Stencil Technology - This paper and presentation was first presented at the 2017 IPC Apex Expo Technical Conference and published in the 2017 Technical Conference Proceedings.
Step UP Stencils:
Material thickness is
increased around specific
components such as edge
connectors, large BGA’s,
D-PAK’s and other devices
to increase the volume of
paste deposited.
STEP TECHNOLOGIES
Step Stencil Technology - This paper and presentation was first presented at the 2017 IPC Apex Expo Technical Conference and published in the 2017 Technical Conference Proceedings.
Currently there are three technologies in North America to manufacture
step stencils.
Micro-Machined Technology Welded Technology Etched Technology
STEP TECHNOLOGIES
Step Stencil Technology - This paper and presentation was first presented at the 2017 IPC Apex Expo Technical Conference and published in the 2017 Technical Conference Proceedings.
Chem-Etch Technology• Historically, the primary
method to manufacture step stencils
• Photographic process applies resist to areas that will not be etched.
• Etchant is sprayed onto surface and removes material until the desired thickness is achieved.
Etched Technology
STEP TECHNOLOGIES
Step Stencil Technology - This paper and presentation was first presented at the 2017 IPC Apex Expo Technical Conference and published in the 2017 Technical Conference Proceedings.
Laser Welded Technology• The area of the step is cut from
the stencil.• The required thickness of the
step area is cut from another foil the exact same size.
• The new foil blank is placed into the cut out area and the foil is welded together.
• Apertures are then laser cut.Laser Welded Technology
STEP TECHNOLOGIES
Step Stencil Technology - This paper and presentation was first presented at the 2017 IPC Apex Expo Technical Conference and published in the 2017 Technical Conference Proceedings.
Micro-Machining Technology• Material is attached to cooled
vacuum plate.• CNC based milling machine
removes very small amounts of material at a time until desired thickness is achieved.
• Stepped foil is mounted to frame and apertures are laser cut. Micro-MachiningTechnology
STEP TECHNOLOGIES
METHOD STEP DEPTH / HEIGHT THICKNESS
STEP SIZE TOLERANCE
POSITIONAL ACCURACY STEP DEPTH / HEIGHT TOLERANCE
FOIL SURFACE
LASER WELDING 2 MILS PER WELD, CAN CUT AND REWELD
+/- 0.3 MILS WITHIN 0.4 MILS MAX OVER TRAVEL STAINLESS +/- 2% OF STEP FOIL THICKNESS
SAME AS MIL FINISH
MICRO-MACHINED DEPENDENT ON FOIL THICKNESS
+/- 1 MIL +/- 0.5 MILS +/- 0.5 MILS BURNISHED FROM ROTATING CUT TOOL
CHEM-ETCH DEPENDENT ON FOIL THICKNESS
+/- 2 MILS +/- 0.5 MILS +/- 0.5 MILS SATIN SEMI-SMOOTH SURFACE
COMPARISON (STRENGTHS & WEAKNESSES) OF STEP TECHNOLOGIES
STEP TECHNOLOGIES
COMPARISON (STRENGTHS & WEAKNESSES) OF STEP TECHNOLOGIES
• CHEM ETCH TECHNOLOGY• HIGH NUMBER OF STEP AREAS• RELIEF STEPS IN BOTTOM OF STENCIL, ie. PLATED VIAS • VERY SMALL APERTURES, <100 MILS• VERY LARGE STEP DOWN AREAS• SEMI-SMOOTH ETCHED SURFACE CAN CATCH/ROB FLUX FROM PASTE
• MICRO-MACHINING TECHNOLOGY• MANY SMALL STEP AREAS• STEP DOWN/UP AREAS IN TENTHS OF A MIL THICKNESSES• AREAS LARGER THAN 2” CAN WARP/DEFORM METAL• BURNISHING AT STEPPED IS SMOOTH, DOES NOT CATCH/ROB PASTE FLUX
• WELDED-STEP TECHNOLOGY• MOST STEP UP AND STEP DOWN STENCILS• LIMITED TO 4” X 4” SIZE FOR LARGE STEPS AND 100 MILS FOR SMALL STEP UP OR DOWN AREAS• MILL FOIL SURFACE AND FOIL THICKNESS TOLERANCE ARE BIGGEST ADVANTAGES
NANO-COATING TECHNOLOGIES
Stencil Nano-Coatings-Do They Improve Repeatability and Uniformity in The Print Process? - This paper and presentation was first presented at the 2018 IPC Apex Expo Technical Conference and published in the 2018 Technical Conference Proceedings.
Benefits of Nano-Coatings• Hydrophobic-repel water based chemistry (flux)
• Oleophobic-repel oil based chemistry (flux)
• Improved Transfer Efficiency (Ceramic)
• Reduced Underside Cleaning Frequency(Ceramic and Self-Assembled Monolayer)
• Reduced Bridging after print (Ceramic and Self-Assembled Monolayer)
NANO-COATING TECHNOLOGIES
Types of Nano-Coatings
• Self Assembled Monolayer• Manually applied to the board side of stencil
• Thickness is 2-4 nano meters
• Clear-no color
• Validation done by testing surface energy
• Can be reapplied
• Primary benefits are reduced underside cleaning and reduced bridging
Stencil Nano-Coatings-Do They Improve Repeatability and Uniformity in The Print Process? - This paper and presentation was first presented at the 2018 IPC Apex Expo Technical Conference and published in the 2018 Technical Conference Proceedings.
NANO-COATING TECHNOLOGIES
Types of Nano-Coatings
• Self Assembled Monolayer-Testing Surface Energy
Stencil Nano-Coatings-Do They Improve Repeatability and Uniformity in The Print Process? - This paper and presentation was first presented at the 2018 IPC Apex Expo Technical Conference and published in the 2018 Technical Conference Proceedings.
NANO-COATING TECHNOLOGIES
Types of Nano-Coatings
• Ceramic • Applied with custom, precision spray equipment• Thickness is 2-4 microns• Color and UV dye• Cured after coating to create a hard, durable coating• Lower Coefficient of Variation in Print Process• Primary benefits are reduced underside cleaning,
reduced bridging, and increased transfer efficiency on small aperture printing
Stencil Nano-Coatings-Do They Improve Repeatability and Uniformity in The Print Process? - This paper and presentation was first presented at the 2018 IPC Apex Expo Technical Conference and published in the 2018 Technical Conference Proceedings.
NANO-COATING TECHNOLOGIES
Types of Nano-Coatings
Self Assembled Monolayer Ceramic-Spray Coat and Cure
Stencil Nano-Coatings-Do They Improve Repeatability and Uniformity in The Print Process? - This paper and presentation was first presented at the 2018 IPC Apex Expo Technical Conference and published in the 2018 Technical Conference Proceedings.
NANO-COATING TECHNOLOGIES
Stencil Nano-Coatings-Do They Improve Repeatability and Uniformity in The Print Process? - This paper and presentation was first presented at the 2018 IPC Apex Expo Technical Conference and published in the 2018 Technical Conference Proceedings.
Test Vehicle
Three stencils, one with SAM coating, one with Ceramic coating and one is uncoated
NANO-COATING TECHNOLOGIES
Stencil Nano-Coatings-Do They Improve Repeatability and Uniformity in The Print Process? - This paper and presentation was first presented at the 2018 IPC Apex Expo Technical Conference and published in the 2018 Technical Conference Proceedings.
Print Parameters
• 50 Boards Printed
• Boards 1, 10, 20, 30, 40 and 50 were measured with a 3D solder paste inspection system (SPI)
• Volume, Height and Area data were collected
Experimental Methodology
NANO-COATING TECHNOLOGIES
Stencil Nano-Coatings-Do They Improve Repeatability and Uniformity in The Print Process? - This paper and presentation was first presented at the 2018 IPC Apex Expo Technical Conference and published in the 2018 Technical Conference Proceedings.
Results
NANO-COATING TECHNOLOGIES
Stencil Nano-Coatings-Do They Improve Repeatability and Uniformity in The Print Process? - This paper and presentation was first presented at the 2018 IPC Apex Expo Technical Conference and published in the 2018 Technical Conference Proceedings.
Results
Printed Solder Paste Transfer Efficiency
• Tukey-Kramer HSD Analysis on Small Area Ratio components
• Evaluates data to determine if it is significantly different
• Ceramic coating mean TE is highest
• SAM coating mean TE is lower than the uncoated stencil
NANO-COATING TECHNOLOGIES
Stencil Nano-Coatings-Do They Improve Repeatability and Uniformity in The Print Process? - This paper and presentation was first presented at the 2018 IPC Apex Expo Technical Conference and published in the 2018 Technical Conference Proceedings.
Results
NANO-COATING TECHNOLOGIES
Stencil Nano-Coatings-Do They Improve Repeatability and Uniformity in The Print Process? - This paper and presentation was first presented at the 2018 IPC Apex Expo Technical Conference and published in the 2018 Technical Conference Proceedings.
Results
Printed Solder Paste HeightTukey-Kramer HSD Analysis:
• 0.4 CSP and 01005 component mean print height SAM coating shows significantly different (lower) print height results when compared to the uncoated and Ceramic coated stencil.
• Ceramic coating mean height results are not significantly different than the uncoated stencil.
NANO-COATING TECHNOLOGIES
Stencil Nano-Coatings-Do They Improve Repeatability and Uniformity in The Print Process? - This paper and presentation was first presented at the 2018 IPC Apex Expo Technical Conference and published in the 2018 Technical Conference Proceedings.
Results
NANO-COATING TECHNOLOGIES
Stencil Nano-Coatings-Do They Improve Repeatability and Uniformity in The Print Process? - This paper and presentation was first presented at the 2018 IPC Apex Expo Technical Conference and published in the 2018 Technical Conference Proceedings.
SEM Analysis
Uncoated ApertureCeramic Nano-Coated Aperture10%-25% TE Improvement
NANO-COATING TECHNOLOGIES
Stencil Nano-Coatings-Do They Improve Repeatability and Uniformity in The Print Process? - This paper and presentation was first presented at the 2018 IPC Apex Expo Technical Conference and published in the 2018 Technical Conference Proceedings.
• There are 2 types of nano-coatings currently being used.
• Self-Assembled Monolayer (SAM)
• Ceramic
• When looking at printed paste volume, Ceramic nano-coatings improve transfer efficiency for 0.66 area ratio apertures and smaller (0.4 CSP and 01005) and SAM nano-coatings decrease printed paste volume when compared to uncoated stencils.
• When area ratios are larger than 0.66, adding SAM nano-coating and Ceramic nano-coating can result in slight increases in printed paste volume when compared to uncoated stencils.
• When area ratios are less than 0.66 (0.4 CSP and 01005), SAM nano-coating decreases the printed height when compared to uncoated stencils. Both Ceramic and uncoated stencil printed height are similar.
Conclusions
NANO-COATING TECHNOLOGIES
Stencil Nano-Coatings-Do They Improve Repeatability and Uniformity in The Print Process? - This paper and presentation was first presented at the 2018 IPC Apex Expo Technical Conference and published in the 2018 Technical Conference Proceedings.
Conclusions
• For components larger than 01005, SAM and Ceramic nano-coatings produced printed paste height slightly higher than the uncoated stencil.
• Printed paste area was higher for the 01005 component on the uncoated stencil.
• Printed paste area was higher for the ceramic nano-coated stencil on the 0.4 CSP, 0.4 QFN and 0.4 QFP components than both the SAM nano-coated stencil and the uncoated stencil.
• When area ratios are less than 0.66 (0.4 CSP and 01005), it is recommended that Ceramic nano-coatings are used to improve repeatability and uniformity in the print process.
• When area ratios are more than 0.66, it is recommended that either Ceramic or SAM nano-coatings are used to improve repeatability and uniformity in the print process.