1 INTRODUCTION
1.1 Background
1.2 Purpose
1.3 Target Audience
2 APPLICABLE DOCUMENTS
2.1 IPC
2.2 Joint Industry Standards
2.3 Telcordia
2.4 ISO
2.5 American Society for Testing and Materials
2.6 Underwriters Laboratories
2.7 International Electrotechnical Commission
3 TYPES OF SOLDER MASK
3.1 Direct Imaging Solder Mask
3.1.1 Screen Imaged (Screen Print)
3.1.2 Ink Jet
3.1.3 Laser Ablated
3.1.4 Coverlay/Punched Film
3.2 Photoimageable Solder Mask
3.2.1 Dry Film (Photoimageable)
3.2.2 Liquid Photoimageable (LPI)
3.2.3 Laser Direct Imageable (LDI)
3.2.4 Photoimageable Coverlay
3.3 Temporary Solder Mask
3.3.1 Peelable
3.3.2 Soluble
4 CHEMICAL COMPOSITION
4.1 Resin Systems
4.1.1 Solvent Borne
4.1.2 Waterborne
4.1.3 100% Solids
4.1.4 Solvent Free Systems
4.2 Pigments and Fillers
4.2.1 Matting Agents
4.2.2 Fillers
4.3 Photoinitiators
4.4 Other Components
4.5 Flame-Retardants
4.6 Curing Systems
5 SOLDER MASK PROPERTIES
5.1 Materials Characterization Tests vs
Performance on Products
5.2 Solder Mask Test Method History
5.3 Chemical Properties of Cured Solder Mask
5.3.1 Resistance to Solvents/Fluxes
5.3.2 Corrosion Resistance
5.3.3 Degree of Cure
5.3.4 Permeability to Moisture
5.3.5 Moisture Absorption
5.3.6 Permeability to Gasses
5.3.7 Outgassing
5.3.8 Nonnutrient
5.3.9 Hydrolytic Stability
5.3.10 Pressurized Steam Resistance (Pressure Cooker
Test)
5.3.11 Ionic Contamination
5.3.12 Flammability
5.4 Thermal Properties of Cured Solder Mask
5.4.1 Thermal Stress/Cycling
5.4.2 Thermal Shock
5.4.3 Thermal Degradation
5.4.4 Thermal Conductivity
5.4.5 Maximum Operating Temperature
5.4.6 CTE
5.4.7 Glass Transition Temperature (Tg)
5.5 Mechanical Properties of Cured Solder Mask
5.5.1 Thickness
5.5.2 Adhesion
5.5.3 Abrasion Resistance
5.5.4 Cracking and Flaking
5.5.5 Shrinkage
5.5.6 Hardness
5.5.7 Machineability
5.5.8 Flexibility
5.5.9 Young's Modulus
5.5.10 Poisson Ratio
5.6 Visual Appearance (Gloss)
5.6.1 Color, Opacity and Transparency
5.7 Electrical Properties of Cured Solder Mask
5.7.1 Dielectric Strength
5.7.2 Dielectric Constant
5.7.3 Dissipation Factor (Loss Tangent)
5.7.4 SIR/Resistivity
5.7.5 Moisture and Insulation Resistance (M&IR)
5.7.6 Volume Resistivity
5.7.7 Comparative Tracking Index (CTI)
5.7.8 Electrochemical Migration
5.7.9 Impedance Concerns
5.8 Shelf Life and Storage
5.9 Pot Life
6 DESIGN ASPECTS
6.1 Choosing a Solder Mask for the Application
6.1.1 Automotive
6.1.2 Aerospace
6.1.3 Telecommunication
6.1.4 Consumer
6.2 Design Considerations and Requirements
6.2.1 Solder Mask Adhesion and Coverage
6.2.2 Solder Mask Clearance
6.3 Impedance Concerns (High Frequency Applications)
6.4 Influence of Solder Mask Thickness on Solder Wetting
6.5 Via Considerations
6.5.1 Size of Holes
6.5.2 Roughness
6.5.3 Plating
6.6 Via Protection
6.6.1 Via Tenting
6.6.2 Via Plugging
6.6.3 Via Filling
6.7 Solder Mask for Hybrids and MCM Packaging
Applications
6.7.1 Organic Substrates for Packaging
7 SOLDER MASKS AND THE APPLICATION PROCESS
7.1 Premask Cleanliness
7.1.1 Verification Prior to Solder Mask
Application
7.1.2 Methods of Precleaning
7.1.3 Influence of Ionic Cleanliness during
Presolder Mask Processes
7.1.4 Surface Roughness
7.2 Application/Coating Methods
7.2.1 Viscosity
7.2.2 Description of Processes
7.3 Tack Drying
7.3.1 Oven Types for Tack Drying
7.3.2 Oven Cleanliness
7.3.3 Process Effects
7.4 Exposure Process (Photoimageable Solder Masks)
7.4.1 Exposure Process Considerations
7.4.2 Exposure Equipment
7.4.3 Image Growth and Undercut
7.5 Developing
7.5.1 Solvent
7.5.2 Aqueous
7.5.3 Effect of Wash Offs
7.5.4 Nozzle Types
7.5.5 Rinsing
7.5.6 Maintenance of Developer Chamber
7.5.7 Waste Treatment for Developing Solution
and Rinsing Water
7.6 Final Cure Mechanisms and Methods
7.6.1 Thermal
7.6.2 UV
7.6.3 LPI
7.6.4 Curing Ovens
7.6.5 Measurement of Cure
7.7 Strippers
7.8 Legend Inks
7.8.1 Legend Inks Effect of Over and Under Cure
of Solder Mask
7.8.2 Cocuring with Solder Mask
7.9 Final Finishes after Solder Mask - Interactions
with Solder Mask
7.9.1 OSP Finishes
7.9.2 HASL
7.9.3 Selective Solder Strip or Selective Reflowed
Tin-Lead or Fused Solder
7.9.4 Plated Final Finishes
7.9.5 Electroless Nickel/Immersion Gold (ENIG) Finish
7.9.6 Immersion Tin (ISn) Finish
7.9.7 Immersion Silver (IAg) Finish
7.9.8 Electrolytic Nickel Gold (Ni/Au) Finish
7.9.9 Electroless Nickel/Electroless Palladium/Immersion
Gold (ENi/EPd/IAu) Finish
7.10 Storage/Packaging Methods for Delayed Processing
7.11 Rework and Repair
7.12 Routing
7.13 Final Fabrication Cleaning
7.14 SPC Methods for Controlling Solder Mask Manufacture
and Processing
8 SOLDER MASK AND SUBSEQUENT PROCESSES
8.1 Assembly
8.2 Preassembly Processes
8.2.1 Preassembly Cleaning
8.2.2 Preassembly Baking
8.3 Reflow Soldering (Solder Pastes)
8.3.1 Solder Paste
8.3.2 Solder Paste Rework
8.3.3 Single-, Double-Sided, and other Soldering
Processes/Technology
8.3.4 Solderballs
8.3.5 Solder Bridges/Shorts
8.3.6 Touch-Up for Insufficient Solder
8.4 SMT Adhesive
8.4.1 Adhesives
8.4.2 Typical Rework of Surface Mount Adhesives
8.4.3 Adhesion of Surface Mount Adhesive to Solder Mask
Surface
8.5 Postassembly Baking
8.6 Underfill/Glob Top/Overmolds
8.6.1 Encapsulants and Potting Compounds
8.6.2 Encapsulants and Wire Bonding
8.7 Lamination
8.8 Wave Soldering
8.8.1 Fluxes
8.8.2 White Staining
8.8.3 Solderballs
8.8.4 Solder Shorts/Bridges
8.8.5 Solder Skips
8.8.6 Inspection
8.8.7 Rework
8.8.8 Process Influences
8.9 Selective Soldering
8.10 Cleaning
8.10.1 Cleaning Agents
8.10.2 Cleaning Methods
8.11 Conformal Coatings
8.11.1 Application Methods of Conformal Coatings
8.11.2 Thickness of Conformal Coating
8.11.3 Viscosity of Conformal Coating
8.11.4 Coatings/Types of Conformal Coating
8.11.5 Compatibility of Conformal Coating
8.11.6 Compatibility Testing of Conformal Coating
8.12 Service Environment Materials
9 INDUSTRY SPECIFICATIONS AND STANDARDS
9.1 IPC-SM-840 Document History (1977 - 2002)
9.1.1 IPC-SM-840 Class 1,2,3 vs. Class T&H
9.1.2 Change in Philosophy between IPC-SM-840B
and IPC-SM-840C
9.2 Bellcore
9.3 IPC-6011
9.4 IPC-6012
9.5 IPC-6013
10 HEALTH AND ENVIRONMENTAL CONSIDERATIONS
10.1 Air Issues
10.2 Water Issues
10.3 Solid/Hazardous Waste Issues
10.4 RoHS/WEEE/Halogen Free Issues
11 TROUBLESHOOTING METHODOLOGY
11.1 Surface Preparation Prior to Application
11.2 Solder Mask Imaging and Developing
11.3 Improper Cure
11.4 Materials Incompatibility
12 EDITORIALS
12.1 Process Change Ethics
12.2 Solder Mask from a Supplier Perspective
12.3 Solder Mask from a UL Perspective
12.4 Solder Mask from a User Perspective (PCB Shop)
12.5 Solder Masks from an OEM Perspective
13 CHALLENGES FOR SOLDER MASK TECHNOLOGY
13.1 High Frequency
13.1.1 Dielectric Constant (Dk)
13.1.2 Dissipation Factor (Df)
13.2 Shrinking Scales/Thicknesses
13.3 Lead Free Solder Temperatures
13.4 Higher Operating Temperatures
13.5 Waterborne
13.6 Legends and Marking Inks
13.6.1 Photoimageable Systems
13.6.2 Ink Jet Systems
13.7 Large Fine Pitch BGA
13.8 Reduced Halogen
13.9 Laser Ablation
13.10 Environmental Regulations (RoHS)
13.11 Solder Mask for Flexible Cable Assembly
13.11.1 Performance Application Recommendations
for Solder Mask over Flex
14 GLOSSARY OF TERMS FOR SOLDER MASK