Custom heat sinks are critical to solar inverter reliability. This guide covers material selection (6063-T5 at 201 W/m·K vs 6061-T6 at 167 W/m·K), CNC machining specs for IGBT mounting faces (±0.005″ flatness, Ra 1.6 µm), surface treatments, and IP65 enclosure integration — from prototype through volume production.
Solar inverters convert DC power from PV arrays to grid-frequency AC using high-speed switching of IGBT or SiC MOSFET modules. These power semiconductors dissipate 1–3% of throughput power as heat — concentrated in junction areas as small as 20×30 mm per module. Managing that thermal density is the primary reliability challenge in inverter design.
IGBT modules (e.g., Infineon EconoPACK, Semikron SKiiP) have maximum junction temperatures of 150–175 °C. Exceeding T_j by even 10 °C halves the module's expected lifetime per Arrhenius reliability models. A well-designed heat sink must keep T_j below the rated maximum under worst-case ambient conditions — typically 50 °C for desert installations per IEC 62109.
Solar inverters operate in ambient temperatures ranging from −40 °C to +60 °C (IEC 62109-1 requirement), with direct solar radiation adding 15–25 °C to enclosure skin temperature. Combined with dust accumulation reducing convective efficiency by 10–20% over time, heat sink designs must include significant thermal margin — typically 15–25% above worst-case calculated requirements.
Modern string inverters pack 50–100 kW into enclosures that housed 10–30 kW a decade ago. This 3–5× increase in power density demands proportional improvements in thermal management — driving the shift from off-the-shelf extruded profiles to application-specific CNC-machined and bonded-fin designs optimized through FEA simulation.
Four primary heat sink construction methods serve solar inverter applications. Selection depends on thermal load, fin geometry requirements, production volume, and cost targets.
| Type | Max Fin Height | Min Fin Thickness | Aspect Ratio | Tooling Cost | Best For |
|---|---|---|---|---|---|
| Extruded | Up to 75 mm (3.0″) | ≥1.3 mm (0.050″) | ≤8:1 | Low ($2K–$8K die) | String inverters, high-volume standard profiles |
| CNC-Machined | Up to 100 mm (4.0″) | ≥0.8 mm (0.031″) | ≤10:1 | None (direct from CAD) | Prototypes, complex geometries, integrated features, low-to-mid volume |
| Bonded-Fin | Up to 150 mm (6.0″) | ≥0.5 mm (0.020″) | ≤20:1 | Medium ($5K–$15K jig) | Central inverters, high-power modules requiring tall fins |
| Cold Plate (Liquid) | N/A (internal channels) | Channel walls ≥1.0 mm | N/A | None–Medium (CNC or brazing jig) | Central inverters >100 kW, high ambient environments, data-center-adjacent installations |
Limited fin aspect ratio, uniform cross-section only, secondary machining for mounting faces
Higher per-unit cost at volume, material waste from subtractive process
Thermal resistance at epoxy bond line (typically +0.1–0.3 °C/W per joint), lower structural integrity than monolithic
Requires coolant loop, pump, and reservoir. Added system complexity and failure modes.
Material choice directly determines thermal performance, weight, machinability, and cost. All thermal conductivity values are at 25 °C per ASM Handbook Vol. 2 and MatWeb verified datasheets.
| Alloy | Thermal Conductivity | Density | Cost | Best For |
|---|---|---|---|---|
| Aluminum 6063-T5 | 201 W/m·K 116 BTU/hr·ft·°F | 2.69 g/cm³ (0.097 lb/in³) | Baseline | Extruded profiles, natural convection heat sinks |
| Aluminum 6061-T6 | 167 W/m·K 96 BTU/hr·ft·°F | 2.70 g/cm³ (0.098 lb/in³) | +5–10% | CNC-machined heat sinks, complex geometries, structural heat sinks |
| Copper C110 (ETP) | 388 W/m·K 224 BTU/hr·ft·°F | 8.94 g/cm³ (0.323 lb/in³) | +200–400% | Heat spreader inserts, cold plates, high-flux zones |
Highest thermal conductivity among common extrusion alloys. Preferred for standard extruded fin profiles where post-machining is minimal.
Superior machinability and strength (40 ksi yield) vs 6063-T5. 17% lower conductivity is typically offset by optimized fin geometry achievable only via CNC.
Nearly 2× the conductivity of aluminum, but 3.3× the density and significantly higher material cost. Typically used as embedded base inserts under IGBT modules rather than full heat sink bodies.
Copper C110 delivers 2× the thermal conductivity of aluminum 6063-T5, but at 3.3× the weight (8.94 vs 2.69 g/cm³). For solar inverter heat sinks, the practical approach is an aluminum body with copper inserts only under the highest heat-flux zones (IGBT die attach areas). Full copper heat sinks are rarely justified in solar applications — the weight and cost penalties outweigh the thermal benefit in most cases.
Upload your CAD files for a quote on CNC-machined or extruded heat sinks. Fast turnaround on prototypes.
CNC-machined heat sinks enable fin geometries and mounting face tolerances unachievable with extrusion alone. These are the key parameters to specify on your engineering drawing.
| Parameter | Value | Notes |
|---|---|---|
| Minimum fin wall thickness | 0.8 mm (0.031″) | Achievable with 3-axis CNC using 1 mm (0.040") end mills. Thinner fins risk deflection during machining and reduce yield. |
| Maximum fin aspect ratio | 10:1 (height:thickness) | Example: 8 mm tall fin at 0.8 mm thick. Higher ratios require slower feeds and workholding support. |
| Fin spacing (forced convection) | ≥2 mm (0.079″) | Minimum practical spacing for forced-air cooling at 2–4 m/s airflow. Narrower spacing increases pressure drop without proportional thermal gain. |
| Fin spacing (natural convection) | 4–6 mm (0.157–0.236″) | Wider spacing required to allow buoyancy-driven airflow. Per Elenbaas correlation, optimal spacing depends on fin height and temperature delta. |
| Mounting face flatness | ±0.005″ (±0.127 mm) | Critical for IGBT/MOSFET thermal interface. Measured per ASME Y14.5-2018 flatness callout over the full mounting area. Tighter flatness (±0.002") available on request with fly-cutting. |
| Mounting face surface finish | Ra 1.6 µm (63 µin) or better | Required to minimize thermal interface resistance with TIM pads. Ra 0.8 µm (32 µin) recommended for bare-die mounting. |
| Base thickness | 4–12 mm (0.157–0.472″) typical | Thicker bases provide lateral heat spreading away from concentrated IGBT footprints. Optimal thickness depends on heat source geometry — FEA recommended. |
| Bolt hole position tolerance | ±0.005″ (±0.127 mm) true position | Per ASME Y14.5-2018 positional tolerance. Ensures alignment with IGBT module bolt patterns (typically M4 or M5 on 40–60 mm spacing). |
The thermal interface between an IGBT module and the heat sink is typically the largest single contributor to junction-to-ambient thermal resistance (θ_ja). A mounting face flatness of ±0.005″ (±0.127 mm) with Ra 1.6 µm allows standard thermal pads (e.g., Bergquist Gap Pad 5000S35, 3.5 W/m·K) to compress evenly at 10–15% compression. Voids from poor flatness can increase local thermal resistance by 2–5× and create hot spots that accelerate module degradation.
IGBT module bolt patterns are standardized by manufacturer (Infineon, Semikron, Mitsubishi). Typical patterns use M4 or M5 screws on 40–60 mm spacing with ±0.005″ (±0.127 mm) true position per ASME Y14.5-2018. Specify tapped holes (not through-holes) to prevent coolant ingress in liquid-cooled designs. Thread depth should be minimum 1.5× bolt diameter.
Thermal interface materials require controlled compression: 10–15% for gap pads, 25–50% for phase-change materials. The heat sink mounting face must be flat enough that the fastener torque (typically 0.8–1.2 N·m for M4) produces uniform pad compression across the entire IGBT footprint. Uneven compression creates thermal resistance gradients and reduces module lifetime.
Surface treatment selection balances thermal emissivity, corrosion resistance, and cost. For outdoor solar installations, the treatment must survive long-term UV, humidity, and thermal cycling.
| Treatment | Spec | Emissivity (ε) | Thickness | Best For |
|---|---|---|---|---|
| Type II Black Anodize | MIL-A-8625, Type II | 0.80–0.88 | 15–25 µm | Exposed heat sinks — significantly improves radiative heat transfer (20–40% of total cooling in natural convection) |
| Type III Hard Anodize | MIL-A-8625, Type III | 0.70–0.80 | 25–75 µm | High-wear environments, sandy/dusty installations. Superior abrasion resistance but higher cost. |
| Chromate Conversion | MIL-DTL-5541, Type II (RoHS) | 0.10–0.20 | <1 µm | Interior heat sinks inside sealed enclosures. Low cost, does not improve radiation but prevents oxidation. |
| Bare Aluminum (As-Machined) | N/A | 0.03–0.07 | N/A | Forced-convection-only applications where radiation is negligible. Not recommended for outdoor use — will oxidize. |
Bare aluminum has an emissivity of only 0.03–0.07, meaning it radiates almost no heat. Type II black anodize increases emissivity to 0.80–0.88 — a 12–30× improvement. For passively-cooled string inverters operating at 80–100 °C surface temperature in still air, this can reduce junction temperature by 8–15 °C. At $0.50–$1.50/part for batch anodizing, it is the highest-ROI thermal improvement available.
Each inverter topology has fundamentally different thermal management requirements. The heat sink approach varies by power level, production volume, and operating environment.
| Parameter | String Inverter | Central Inverter | Microinverter |
|---|---|---|---|
| Power Range | 3–100 kW | 100 kW–5 MW | 200–500 W |
| Thermal Dissipation | 50–300 W | 1–15 kW | 5–15 W |
| Heat Sink Type | Extruded or CNC-machined | Bonded-fin or cold plate | Die-cast or stamped |
| Primary Material | 6063-T5 / 6061-T6 | 6061-T6 + copper inserts | ADC12 die-cast |
| Cooling Method | Natural + forced convection | Liquid or hybrid | Natural convection only |
| Production Volume | 10K–500K/yr | 100–10K/yr | 100K–10M+/yr |
| Key Challenge | Compact IP65 passive cooling | Very high thermal density | Extreme cost sensitivity |
Outdoor IP65 enclosure with passive cooling requires high fin surface area within compact form factor
Very high thermal density from paralleled IGBT modules. Often requires liquid cooling or bonded-fin assemblies with >100 mm fin height.
Extremely cost-sensitive. Heat sink often doubles as enclosure. Module-level electronics must survive long-term outdoor exposure.
Solar inverter heat sinks rarely exist in isolation — they must integrate with sheet metal enclosures that provide environmental protection, EMI shielding, and structural support. The heat sink–enclosure interface is a critical design feature.
The heat sink mounts to the enclosure wall via a machined flange with a compressed gasket (silicone or EPDM, Shore A 40–60) in a CNC-machined groove. Groove depth is typically 1.5 mm for a 2.0 mm cross-section O-ring cord. Bolt spacing should not exceed 60 mm to maintain uniform gasket compression for IP65 per IEC 60529.
The enclosure opening for heat sink pass-through requires ±0.010" (±0.254 mm) tolerance on the cutout dimensions with deburred edges (break 0.2–0.5 mm radius) to prevent gasket damage. Material: typically 1.5–2.0 mm 5052-H32 or powder-coated SGCC galvanized steel. Laser cutting or CNC punching recommended for consistent edge quality.
When the heat sink is the primary thermal path, the enclosure wall temperature near the pass-through can reach 70–90 °C. Use thermal standoffs or insulating gaskets (e.g., silicone foam, k ≤ 0.2 W/m·K) between the heat sink flange and enclosure to prevent excessive heating of internal components and cable insulation.
Inverter enclosures typically provide EMI shielding per IEC 61000-6-2/6-4. The heat sink pass-through creates a gap in the shielding. Conductive EMI gaskets (beryllium copper finger stock or conductive silicone) around the heat sink perimeter maintain shielding integrity. Contact resistance should be <50 mΩ across the joint.
Upload your CAD files for a detailed quote. CNC-machined aluminum heat sinks with ±0.005″ IGBT mounting flatness — from prototype through production volumes.
Get Free Quote FastWe use cookies to improve the site and track RFQ conversions. Privacy Policy. Allow non-essential cookies?