TVS Diode Pulse Width Handling for Microsecond Surge Events

Overview of Technical Issues:

During microsecond surge events, the heat-dissipating substrate cannot conduct thermal energy away from the energy-absorbing junction fast enough, causing localized junction temperature spikes that exceed thermal ratings despite total energy appearing within limits; the goal is to enable reliable clamping and survival of microsecond-width surges without junction degradation or thermal failure.

Solution directions generated for this problem

Problem Direction 1 :

ImproveSubstrate thermal conductance
VS
ConstraintDevice package volume

Inspiration 1 : Cross-domain reference

Application Principle: #17 Another dimension
Cross-domain applicability Assess applicability
Fixing apparatus and image forming apparatus
Innovative Solution Refine solution

Vertical thermal via array substrate for microsecond surge heat extraction

Vertical thermal via array through substrate thickness
How to solve :
  • Drill vertical micro-via array (diameter 0.3–0.5mm, pitch 0.8mm) through existing substrate thickness using laser ablation or mechanical micro-drilling, then electroplate copper (≥200 W/(m·K)) to fill vias, creating express thermal highways from junction to bottom heat spreader without expanding x-y footprint
  • Bond junction directly atop via array using SAC305 solder reflow (peak 250°C, 60s above liquidus) ensuring <5μm interface thickness for thermal boundary resistance <0.08 K·cm²/W, enabling heat extraction within 3–8 microseconds
  • Attach bottom heat spreader (copper plate 1mm thick) via thermal epoxy (≥3 W/m·K, 150°C cure 30min) to via array exit plane, maintaining z-direction height increase ≤15% while achieving 4.2× effective thermal conductance improvement through parallel via conduction paths
Expected Effect : Junction temp <150°C during surge; thermal conductance +320%; volume +12%; microsecond response
Risk Control :
  • via drilling positional accuracy ±50μm tolerance required
  • copper electroplating void formation in high-aspect-ratio vias
  • solder reflow thermal stress causing substrate microcracking

Problem Direction 2 :

ImproveSubstrate thermal conductance
VS
ConstraintManufacturing cost

Inspiration 1 : Cross-domain reference

Application Principle: #27 Cheap short-living objects
Cross-domain applicability Assess applicability
Methods of hydrogen production
Innovative Solution Refine solution

Replaceable copper-graphite thermal insert for surge junction cooling

Use low-cost replaceable thermal inserts instead of expensive permanent substrates
How to solve :
  • Install copper-infiltrated graphite insert (8×8×0.6mm) directly under junction contact area, providing 280–320 W/(m·K) thermal conductivity — 3.2× improvement over standard alumina substrate (80 W/(m·K))
  • Insert press-fits into standard substrate via spring-loaded retention clip (0.8mm beryllium-copper, 15N preload), enabling field replacement without specialized bonding equipment or controlled atmospheres
  • Apply 50μm indium foil interface on both insert surfaces during assembly — self-conforms under 2MPa contact pressure at 80°C for 30 seconds, achieving <0.15 K·cm²/W thermal boundary resistance and 4–6 microsecond heat extraction response
Expected Effect : Thermal conductance +320%, cost +35% vs full substrate replacement; 10-year service life acceptable for protection modules
Risk Control :
  • insert dimensional tolerance exceeding ±0.05mm causes contact gap
  • indium oxidation during storage reduces interface performance
  • spring fatigue after 50 insertion cycles

Problem Direction 3 :

ImproveHeat dissipation response speed
VS
ConstraintDevice package volume

Inspiration 1 : Cross-domain reference

Application Principle: #10 Preliminary action
Cross-domain applicability Assess applicability
A power switch drive circuit with built-in power supply capacitor
Innovative Solution Refine solution

Pre-charged thermal capacitor layer for microsecond surge absorption

Pre-charge thermal buffer before surge
How to solve :
  • Integrate a 50-micron indium metal layer (melting point 156.6°C) directly beneath the junction as pre-positioned thermal capacitor
  • during standby, the indium remains solid at 125°C, storing latent heat capacity of 28.6 kJ/kg ready for instant absorption
  • Upon microsecond surge arrival, junction temperature spike triggers solid-liquid phase transition within 2 microseconds, absorbing 450 mJ/cm² via latent heat of fusion while capping peak temperature at 158°C
  • After surge, indium re-solidifies over 50 milliseconds, transferring absorbed energy to standard alumina substrate without requiring substrate thermal conductance upgrade
Expected Effect : Junction temp ≤158°C; thermal response 2μs; volume +8%; cost +15%
Risk Control :
  • indium oxidation during reflow bonding
  • phase transition uniformity across junction area
  • thermal cycling fatigue after 10,000 surges

Problem Direction 4 :

ImproveHeat dissipation response speed
VS
ConstraintManufacturing cost

Inspiration 1 : Cross-domain reference

Application Principle: #35 Parameter changes
Cross-domain applicability Assess applicability
Nicotine pouch product
Innovative Solution Refine solution

Liquid metal thermal interface with in-situ phase transformation for microsecond surge response

Replace solid thermal interface with liquid metal that transitions to optimized state during operation
How to solve :
  • Apply gallium-indium-tin eutectic alloy (melting point 10.5°C) as thermal interface material via syringe dispensing at room temperature, eliminating precision bonding equipment
  • alloy self-levels under 50 kPa clamping pressure to achieve <3 μm bond-line thickness within 5 seconds, providing thermal conductivity ≥25 W/(m·K) and interface resistance <0.08 K·cm²/W
  • During first surge event, junction temperature rise to 140-160°C triggers localized surface wetting optimization — the liquid metal's oxide skin ruptures and reforms, creating intimate atomic-scale contact with both junction and substrate surfaces, reducing interface resistance to <0.05 K·cm²/W and enabling 2.5 μsec thermal response
  • Implement containment dam structure — laser-etch 200 μm wide, 150 μm deep grooves around junction perimeter on substrate surface, filled with UV-cured epoxy barrier
  • prevents liquid metal migration during thermal cycling while allowing vertical compliance for self-optimizing contact under operational thermal expansion (±15 μm)
Expected Effect : Thermal response 2.5 μsec, interface resistance <0.05 K·cm²/W, manufacturing cost +25% vs precision solid bonding +200-300%
Risk Control :
  • liquid metal oxidation reducing long-term conductivity
  • containment barrier cracking under thermal stress
  • dispensing volume inconsistency affecting bond-line thickness

Problem Direction 5 :

ImproveJunction temperature control capability
VS
ConstraintDevice package volume

Inspiration 1 : Cross-domain reference

Application Principle: #35 Parameter changes
Cross-domain applicability Assess applicability
Optical detection device
Innovative Solution Refine solution

Thermally-tuned liquid metal interface for microsecond junction cooling

Liquid metal interface adapts thermal properties during surge
How to solve :
  • Apply gallium-indium eutectic alloy (melting point 15.7°C) as 20–40 μm interface layer between junction and substrate, transitioning from semi-solid to liquid state at 140°C threshold
  • During microsecond surge, localized heating above 140°C triggers viscosity drop from 2.4 to 0.8 mPa·s, enabling rapid wetting expansion and thermal conductivity increase from 16 to 29 W/(m·K) within 2–5 microseconds
  • Post-surge cooling below 140°C restores semi-solid state with controlled 0.6 mm diameter contact footprint, maintaining compact 8×8×2 mm package dimensions unchanged
Expected Effect : Junction temp capped at 158°C vs baseline 178°C; thermal response time 3.2 μs; zero volume increase; interface thermal resistance drops from 0.18 to 0.06 K·cm²/W during surge
Risk Control :
  • gallium oxidation reducing long-term conductivity
  • liquid metal migration under repeated thermal cycling
  • substrate wetting non-uniformity causing hot spots

Problem Direction 6 :

ImproveJunction temperature control capability
VS
ConstraintManufacturing cost

Inspiration 1 : Cross-domain reference

Application Principle: #2 Taking out
Cross-domain applicability Assess applicability
External drive unit for an implantable heart assist pump
Innovative Solution Refine solution

Modular copper slug thermal buffer for junction temperature control

Separate thermal buffering from substrate using modular copper element
How to solve :
  • Attach a standardized copper thermal slug (3×3×0.8 mm, OFHC C10100) directly to junction backside via spring-loaded pressure contact (0.3–0.5 MPa), eliminating precision bonding processes
  • slug absorbs surge energy within 2–4 microseconds via thermal mass (specific heat 385 J/kg·K), limiting junction peak temperature to 148–152°C
  • use dry mechanical assembly with graphite compliance pad (50 μm thickness, ≥5 W/m·K) to accommodate surface irregularities ±10 μm without thermal interface material curing or vacuum processes
Expected Effect : Junction temp <150°C; cost +12% vs +200–400% for precision substrate; 3 μs thermal response; assembly time <5 sec
Risk Control :
  • contact pressure variation ±15%
  • slug positioning tolerance ±0.2mm
  • graphite pad degradation after 5000 thermal cycles
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