TVS Diode Package Thermal Resistance Comparison for Power Design

Overview of Technical Issues:

Different TVS diode package structures provide insufficient heat conduction from the chip to external cooling interfaces due to varying thermal resistance values, causing junction temperature to rise beyond safe limits during power surge events and compromising circuit protection reliability; the goal is to compare package thermal resistance characteristics to select optimal thermal performance for the required power dissipation level.

Solution directions generated for this problem

Problem Direction 1 :

ImprovePackage thermal conductivity
VS
ConstraintPackage structure complexity

Inspiration 1 : Cross-domain reference

Application Principle: #2 Taking out (Extraction)
Cross-domain applicability Assess applicability
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Innovative Solution Refine solution

Independent thermal slug extraction for TVS diode packages

Extract heat path from package body using independent thermal element
How to solve :
  • Separate the thermal function by attaching a copper thermal slug (0.6mm thick, ≥380 W/(m·K)) directly beneath the TVS chip via solder reflow at 260°C, while maintaining standard molded package body for electrical connections
  • The slug extends through a bottom-side opening in the molding compound, creating a direct thermal path from chip to PCB without adding internal package layers or complexity
  • Quality control: measure slug-to-chip bond line thickness ≤50μm via cross-section inspection, verify thermal resistance ≤18°C/W using transient thermal testing per JESD51-1, ensure slug coplanarity within ±0.1mm
Expected Effect : Thermal resistance 18°C/W; junction temp <145°C during surge; package assembly unchanged
Risk Control :
  • slug-chip interface voiding >5%
  • slug position misalignment
  • molding compound adhesion to slug

Problem Direction 2 :

ImprovePackage thermal conductivity
VS
ConstraintManufacturing cost

Inspiration 1 : Cross-domain reference

Application Principle: #1 Segmentation
Cross-domain applicability Assess applicability
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Innovative Solution Refine solution

Modular thermal cap with standard molded body for TVS packages

Divide package into low-cost molded body and separate thermal cap
How to solve :
  • Design standard injection-molded epoxy body using conventional materials and processes for electrical insulation and mechanical protection, accounting for 85% of package volume
  • Manufacture separate clip-on thermal cap (3mm × 3mm × 0.6mm) from high-conductivity copper alloy (≥380 W/m·K) with precision-stamped mounting tabs, directly contacting chip top surface via pre-applied phase-change interface material (melting point 58°C, thermal conductivity ≥3 W/m·K)
  • Assemble thermal cap onto molded body after standard die attach and wire bonding, using mechanical snap-fit retention requiring no additional bonding process, concentrating thermal enhancement cost to <15% of total package area
Expected Effect : Thermal resistance 16-19°C/W; cost increase limited to 1.4×; junction temperature maintained below 145°C during 8/20μs surge events
Risk Control :
  • thermal cap alignment tolerance (±0.1mm required)
  • phase-change material squeeze-out during cap assembly
  • long-term mechanical retention reliability under thermal cycling

Problem Direction 3 :

ImproveHeat dissipation efficiency
VS
ConstraintManufacturing cost

Inspiration 1 : Cross-domain reference

Application Principle: #2 Taking out (Extraction)
Cross-domain applicability Assess applicability
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Innovative Solution Refine solution

Direct chip-to-PCB thermal extraction via embedded copper pillar array

Extract heat directly from chip to PCB bypassing package
How to solve :
  • Remove intermediate thermal path through package body by mounting chip on copper pillar array (0.6mm diameter, 1.2mm pitch) embedded in PCB substrate, pillars directly contact chip backside via solder reflow at 260°C
  • Pillars fabricated using standard PCB via-filling process with electroplated copper (≥380 W/(m·K) conductivity), eliminating need for specialized lead frames or ceramic substrates
  • Package molding compound serves only electrical insulation and mechanical protection, not thermal path, allowing low-cost epoxy resin instead of thermally-enhanced materials
Expected Effect : Thermal resistance 12–16°C/W; manufacturing cost +15% vs standard packages; junction temperature <140°C during 8/20μs surge
Risk Control :
  • copper pillar coplanarity tolerance exceeds ±25μm causing incomplete chip contact
  • solder void formation >5% reducing thermal contact area
  • PCB warpage during reflow affecting pillar-to-chip interface quality

Problem Direction 4 :

ImproveCircuit protection reliability
VS
ConstraintPackage structure complexity

Inspiration 1 : Cross-domain reference

Application Principle: #3 Local quality
Cross-domain applicability Assess applicability
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Innovative Solution Refine solution

Spatially-graded thermal interface material for TVS diode packages

Apply graded thermal conductivity TIM to concentrate heat removal at chip hotspot
How to solve :
  • Design dual-zone thermal interface material with high-conductivity core (≥200 W/(m·K) graphene-silver composite) covering chip center 40% area and standard TIM (3 W/(m·K) silicone) for peripheral zones
  • Pre-fabricate TIM as drop-in insert with 0.05mm thickness tolerance, cured at 150°C for 2 hours, enabling standard single-layer package assembly without structural modification
  • Position high-conductivity zone via optical alignment to ±0.1mm accuracy during die attach, ensuring thermal resistance <18°C/W at chip center where current density peaks during surge events
Expected Effect : Junction temp maintained 125-145°C; thermal resistance 17°C/W; no added package layers
Risk Control :
  • TIM zone misalignment during assembly
  • graphene-silver composite cost variability
  • long-term delamination at material interface

Problem Direction 5 :

ImproveCircuit protection reliability
VS
ConstraintManufacturing cost

Inspiration 1 : Cross-domain reference

Application Principle: #11 Beforehand cushioning (Prior cushioning)
Cross-domain applicability Assess applicability
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Innovative Solution Refine solution

Thermal margin design with relaxed tolerance for cost-effective TVS protection

Design thermal path with built-in safety margin to enable relaxed manufacturing tolerances
How to solve :
  • Target thermal resistance of 15°C/W instead of 20°C/W to create 25% thermal margin, allowing junction temperature to stay within 125-150°C even with manufacturing variations of ±15%
  • Use standard copper lead frame (0.6mm thickness) with direct die attach via silver-filled epoxy (≥200 W/(m·K)), eliminating precision multi-layer stacking and reducing material cost by 40%
  • Implement statistical process control with thermal resistance acceptance range 12-18°C/W (±20% tolerance vs industry ±5%), enabling standard die bonding equipment without costly precision alignment systems
Expected Effect : Manufacturing cost +35% vs +200-400%; junction temperature maintained 125-150°C under all surge conditions; production yield improved from 85% to 96%
Risk Control :
  • thermal margin erosion over product lifetime
  • silver epoxy voiding during cure
  • lead frame flatness variation affecting die contact
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