With the rapid development of new energy vehicles, rail transit, photovoltaic power generation and other fields, the requirements for packaging materials for power semiconductor devices are becoming increasingly high. Insulated Gate Bipolar Transistor (IGBT), as the core device for energy conversion and control, is known as the "leader" in the field of power electronics; CPU"。 The harsh conditions such as high temperature, high humidity, and mechanical vibration generated during its working process pose severe challenges to the sealing materials.

At present, the mainstream high-power IGBT modules generally use the double-layer composite packaging structure of silicon gel+epoxy potting adhesive: the inner layer uses silicone gel to provide electrical insulation protection, and the outer layer usesEpoxy sealantProvide mechanical strength support. This article will systematically introduce the core advantages and application points of epoxy sealant in IGBT module packaging.

1、 What is IGBT module sealant?

1.1 Introduction to IGBT module

IGBT is a power semiconductor device that combines the advantages of high input impedance of MOSFET and low conduction voltage drop of bipolar transistor. It has the characteristics of simple driving, fast switching speed, and large on state current. Mainly used in the fields of new energy vehicle motor controllers, rail transit traction converters, photovoltaic/wind power inverters, industrial frequency converters, and smart home appliances.

1.2 Why is sealing necessary?

IGBT modules face multiple environmental pressures during operation: thermal stress (chip temperature can reach 150-200 ℃), electrical stress (high voltage can reach over 3300V), mechanical stress (vibration and impact causing wire breakage), and environmental erosion (moisture salt spray corroding metal components). Sealing adhesive is a key packaging material introduced to solve the above problems.

Comparison of Common Sealing Adhesive Types:

2、 Eight core properties of epoxy sealant

Epoxy sealant is composed of special epoxy resin, curing agent, inorganic filler, and functional additives, and is one of the more widely used electronic packaging materials. Its core advantages are as follows:

1. Excellent mechanical protection capability

After solidification, it forms a hard and dense protective shell, effectively resisting external impacts and vibrations

2. Zhuoyue's chemical and environmental resistance

Can resist the erosion of chemical substances such as acid, alkali, and oil, and block moisture and salt spray

3. High electrical insulation

High volume resistivity and high dielectric strength, preventing high-voltage leakage and breakdown

4. Excellent thermal stability

Can withstand a wide temperature range of -40 ℃ to+200 ℃

5. Anti oxidation and anti-corrosion

Completely enclose the internal space, isolate oxygen and moisture, and reduce the risk of lead solder joint oxidation

6. Improve long-term reliability

Can effectively extend the service life of IGBT modules by 2-3 times

7. The formula has strong customizability

Hardness adjustable from Shore D70 to D90+, supporting room temperature to medium temperature curing

8. Strong adhesion ability

Can form strong adhesion with various substrates such as copper, aluminum, ceramics, etc

3、 Special requirements of IGBT module for potting adhesive

Compared with traditional electronic component encapsulation, high-power IGBT modules have higher requirements for encapsulation materials:

High insulation strength - guarantee; Three Integration Points "; Insulation reliability of (chip bonding wire potting adhesive interface)

• No by-products curing - avoid residual bubbles affecting dielectric performance

Extreme temperature resistance - the internal working temperature can reach 180-200 ℃ and needs to be maintained stable for a long time

• Resistance to moisture and impact - requires passing the 85 ℃/85% RH standard test and temperature cycling (-40 ℃) ↔+ 125℃）

 CTE coefficient of thermal expansion matching - more critical indicators

The CTE of epoxy resin is usually 30-60ppm/℃, while silicon chips are about 2.6ppm/℃ and copper liners are about 17ppm/℃. CTE mismatch can generate significant internal stress during temperature cycling, leading to cracking of the encapsulated body, detachment of the shell, or breakage of the bonding wire. Reducing CTE values and improving component compatibility is one of the core directions of research and development.

4、 Practical application: Double layer composite sealing process

4.1 Packaging Form and Encapsulation Method

4.2 Double layer composite sealing process flow

Step 1: IGBT chip mounting → Step 2: bonding wire interconnection → Step 3: silicone gel pouring (inner layer)

→ Step 4: gel curing → Step 5: epoxy adhesive secondary filling (outer layer reinforcement)

→ Step 6: Curing and Forming → Testing and Acceptance

" First gel, then epoxy" Advantages of the plan:

• Inner layer silicon gel: provide flexible buffer and absorb thermal stress; Excellent electrical insulation to prevent partial discharge

• Outer epoxy layer: forms a hard shell, providing mechanical strength and environmental isolation

This scheme is particularly widely used in high-voltage IGBT modules for rail transit.

4.3 Technological Development Direction

5、 Experimental verification and selection suggestions

5.1 Reliability Testing Standards

Typical testing items for domestic epoxy potting adhesive in IGBT module packaging include:

5.2 Selection Points

1. Clarify the application scenario - working temperature range, voltage level, and whether it is for outdoor use

2. Confirm process conditions - does it support vacuum infusion? What is the upper limit of the curing oven temperature?

3. Focus on key parameters - prioritize CTE values Tg、 Three major indicators of dielectric strength

4. Pay attention to supplier qualifications - whether there are IGBT industry cases and third-party testing reports

5. Small batch validation first - import in bulk after completing reliability testing

summary

Epoxy sealant plays an indispensable role in high-power IGBT module packaging due to the mechanical strength, electrical insulation, and environmental resistance of Zhuoyue. Although there are technical challenges such as CTE matching, these problems have been effectively solved through reasonable formula design and double-layer composite potting process (silicon gel+epoxy adhesive). Choosing an epoxy sealant product with good CTE matching and fully verified reliability is a crucial step in ensuring product quality and long-term reliability.

In the future, epoxy sealant is continuously developing towards ultra-low CTE system (<15ppm/℃), high thermal conductivity, rapid curing, and environmentally friendly halogen-free flame retardant.