An overview of how solder paste cools down chips?

By optimising the thermal conductivity of the material, strengthening the metallurgical connection structure and adapting the alloy design to different application scenarios, solder paste achieves efficient heat dissipation of the chip, and its cooling mechanism can be analysed from the following three levels:

I. Material innovation: high thermal conductivity alloy to build heat dissipation channel

The traditional silver adhesive relies on epoxy resin bonding, the thermal conductivity of silver powder filling is only 5-15W/m-K, and silver migration is likely to occur at high temperatures, resulting in an increase in resistivity. And solid crystal solder paste using high-purity tin-based alloys (such as SnAgCu, SnSb), its thermal conductivity of up to 60-70W/m-K, more than 5 times that of silver glue. For example, a power module manufacturers in the IGBT package after the use of solid crystal solder paste, the chip junction temperature from 125 ℃ to 105 ℃, a reduction of 16%, in full compliance with the JEDEC JESD51 thermal test standards, the module life extension of 30%. This feature is particularly important for the power density of more than 100W/cm² SiC, GaN and other third-generation semiconductor devices, can effectively avoid performance degradation and failure due to overheating.

II. structure strengthening: metallurgical bonding to enhance the efficiency of heat transfer

Solid crystal solder paste through the reflow soldering intermetallic compound (IMC) layer, so that the solder joints have excellent mechanical strength (shear strength of more than 40MPa, 2-3 times that of silver glue). This metallurgical bond not only enhances the robustness of the connection, but also optimises the heat transfer path:

Micro level: The IMC layer eliminates the thermal resistance of the organic binder in the silver adhesive, allowing heat to be transferred directly through the metal lattice;

Macro level: the contact area between the solder joints and the chip and substrate is larger, reducing the interfacial loss of heat transfer. For example, in Mini LED chip packaging, the ultra-fine powder of solid crystal solder paste accurately fills the gap between the chip and the ceramic substrate, and the thermal resistance of the solder joints is reduced by 40%, which effectively reduces the LED light degradation (luminous flux decline of <5% in 1000 hours).

III.Scenario adaptation: alloy design to meet differentiated needs

For different chip temperature resistance, power density and process requirements, solder paste by adjusting the alloy composition to achieve precise heat dissipation:

High-temperature scenarios (temperature resistance >150℃):

Adopting high-temperature SnAgCu alloy (melting point ≥217°C), the solder joints can withstand long-term working temperature of 150°C, and the strength decreases <5% after aging at 150°C for 1000 hours. For example, in high-voltage fast charging, server power supply and other scenarios, this type of solder paste ensures the stability of the chip at extreme temperatures.

Medium Temperature Scenarios (Temperature Resistance ≤ 150°C)

The peak soldering temperature of medium temperature SnBi/SnAgBi alloy (melting point 138-172°C) can be controlled within 190°C, avoiding damage to the heat-sensitive chip, and is compatible with reflow and laser soldering processes, suitable for LEDs, CIS sensors and other devices.

Extreme heat dissipation needs (power >200W):

High-conductivity solid crystal solder paste (with Cu/Ni enhancement phase) will increase the thermal conductivity to more than 70W/m-K. Used with copper substrate, it can reduce the junction temperature of the chip by 20℃ and significantly improve the life of the device. For example, in solid-state LIDAR transmitter modules, this type of solder paste becomes a key heat dissipation material.

IV.process synergy: fine control to protect the thermal performance

The cooling effect of solder paste also depends on the precise control of process parameters:

Powder particle size: gap <50μm precision scenes need to choose 5-10μm T7 grade powder, with low viscosity formula to ensure that the solder joints are filled evenly;

Environmental adaptability: high humidity and high vibration environments need to use halogen-free formulations to ensure that the surface insulation resistance of the residue >10¹³Ω, to avoid electrochemical corrosion;

Welding process: by optimising the reflow temperature profile, so that the IMC layer thickness is controlled at 1-3μm, both to ensure mechanical strength, but also to avoid thermal resistance increase due to IMC overthickness.

Summary: the core value of solder paste cooling

Through the triple optimisation of material, structure and process, solder paste transforms the connection between the chip and the substrate from "fragile adhesion" to "solid welding", which fundamentally solves the heat dissipation problem of high-power devices. Its value is not only reflected in the reduction of chip temperature and extension of life, but also in the third generation of semiconductors, advanced packaging (such as AI chips, GPUs) and other high-density integration scenarios to provide a reliable heat dissipation solution, and has become an indispensable key material in high-end electronics manufacturing.