Die Product Assembly Options

A wide variety of die assembly methods are available for implementation into high yeild, high reliability systems. Some of the options are reviewed here for comparison.

Die Attach Methods for COB

Thermoset Adhesive

• Advantages: low cure temperature, low modulus of elasticity, high strength, relatively inexpensive, wide process window (bondline, curetime)
• Disadvantages: resin bleed, level of thermal/electrical conductivity, limited reworkability, limited internal water vapor (RGA) performance
• Process Considerations: cure profile, bleedout evaluation, material compatibility, design rules, pot life and storage, dispensing considerations/patterns/voiding, bondline control, placement accuracy/planarity
  

Thermoplastic Adhesive

• Advantages: low cure temperature, low modulus of elasticity, relatively inexpensive, reworkable
• Disadvantages: limited strength, electrical/thermal conductivity, limited internal water vapor (RGA) performance, manufacturing logistics in handling
• Process Considerations: force, time, pressure, placement accuracy/planarity/bondline, thermal heirarchy
  

Metal-Filled Glass

• Advantages: high thermal/electrical conductivity, high temperature tolerance, excellent internal water vapor performance (RGA), strength, mid-range modulus of elasticity
• Disadvantages: bond line control, cost, non-reworkable, fillet control, die size limitations, high temperature organic burn-out
• Process Considerations: bond line control, OBO profile, dispense control/voiding, placement accuracy, die size, metallurgy of die backside
  

Au-Si Eutectic

• Advantages: high thermal/electrical performance, strength, RGA, temperature tolerance, reworkable
• Disadvantages: cost, high modulus of elasticity, limited die size, potential for chip damage, high process temperature, narrow process window
• Process Considerations: process profile, environment (N₂, forming gas), die size, metallurgy(type & oxidation), voiding, collet size/design
  

Soft Solder

• Advantages: good thermal/electrical performance, reworkable, good matching for dissimilar CTE's
• Disadvantages: special backside metalization required, typically need forming gas and nitrogen atmosphere, die placement issues
• Process Considerations: level of O₂ in atmosphere, oxidation on surfaces, solder splash during placement, voiding

Interconnect Methods for COB

Gold-Ball Bond

• Advantages: high throughput, high strength, omni-directional, fine pitch
• Disadvantages: elevated temperature, increased material cost, intermetallic potential
• Process Considerations: temperature, power, force, time, wire diameter, wire length, metallurgy, pitch, bonding surface conditions, bonding area
  

Aluminum Wedge Bond

• Advantages: room temperature processing, lower material cost (wire), fine pitch
• Disadvantages: Strength, throughput, not optimum for non-hermetric applications
• Process Considerations: power, force, time, wire diameter, wire length, metallurgy, pitch, bond angle, forward/reverse bonding, bonding surface conditions, bonding area
  

Seal and Encapsulation Methods

Hermetic – Seam Seal

• Advantages: hermetic, low temperature, large seal area, low profile, minimal floor space requirements
• Disadvantages: low throughput
• Process Considerations: dry box environment, electrode design, lid design

Non-Hermetic – Glob Top

• Advantages: flexible, low temperature, low stress, low profile
• Disadvantages: non-hermetic, limited protection, spread, wire wash potential
• Process Considerations: dispensing parameters, viscosity, dams, cure

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