Ag Fired Cap Bonding for Copper-Wire Power Semiconductor Reliability
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Solution Overview
Problem
Conventional semiconductor devices with aluminum wires exhibit insufficient power cycle capabilities due to increasing junction temperatures, and while copper wires or lead materials are used as alternatives, they either require excessive ultrasonic power for bonding, leading to device breakage or result in decreased power cycle lifetime due to high thermal resistance.
Innovation Solution
A semiconductor device with a high-thermal-resistant fired layer covering the electrodes on the semiconductor chip, which buffers the ultrasonic wave power and reduces stress on the bonding materials, improving the power cycle capability by using a high-thermal-resistant fired layer such as silver or copper fired caps, and employing Pb-free solder with an Ag fired cap structure to reduce cumulative equivalent strain.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If copper wires are used instead of aluminum wires to prolong lifetime, then power cycle capability is improved, but ultrasonic wave power becomes extremely large causing device breakage
Solution Approach 1:
A fired cap layer is introduced as an intermediary between the copper wire and the electrode. This fired cap absorbs the excessive ultrasonic energy during wire bonding, preventing direct transmission of harmful vibrations to the device while still enabling reliable electrical connection. The fired cap acts as a buffer that mediates the bonding process between the wire and electrode.
Solution Approach 2:
The invention changes the physical state and properties of the cap material through firing process. The organic binder is removed and inorganic components are sintered to form a rigid, thermally stable structure that can withstand ultrasonic bonding without transmitting excessive stress to the device.
2Device complexity
If Pb-free solder is used with upper wirings to avoid ultrasonic bonding issues, then device complexity is reduced, but power cycle lifetime decreases due to high thermal resistance
Solution Approach 1:
The invention uses a composite structure consisting of a metal cap (silver or copper) combined with a fired organic-inorganic hybrid material. This composite provides both the electrical conductivity needed for upper wiring connections and the thermal management properties required for high-temperature operation, resolving the contradiction between electrical functionality and thermal performance.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution effectively prevents device breakage during bonding, enhances power cycle capability, and maintains or improves power cycle lifetime by reducing stress and strain on the bonding materials, even at elevated junction temperatures.
Implementation Method 1
a high-thermal-resistant fired layer formed so as to cover at least a part of the electrode formed on the front surface side of the semiconductor chip
Implementation Method 2
high-thermal-resistant fired layer
Data Source
AI summary
A semiconductor device includes: a semiconductor chip; and an Ag fired cap formed so as to cover a source pad electrode formed on the semiconductor chip. The semiconductor chip is disposed on a first substrate electrode, and one end of a Cu wire is bonded onto the Ag fired cap by means of an ultrasonic wave. There is provided a semiconductor device capable of improving a power cycle capability, and a fabrication method of such a semiconductor device.