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From New Wire Bonding Techniques and Types of Wire Bonding, to the Challenges of Working with Small MESA Chips- What You Need to Know About the Process

Posted on Monday, March 12, 2018
From New Wire Bonding Techniques and Types of Wire Bonding, to the Challenges of Working with Small MESA Chips- What You Need to Know About the Process

Small MESA devices have posed a number of wire-bonding challenges, which have required advancements in wire-bonding technologies and skills. As MESA chip size has shrunk and market forces necessitate faster processes with higher yields, the difficulty around wire bonding MESA devices has only expanded. Overcoming these challenges requires not only the latest in wire-bonding equipment, but the process development know-how, and specially designed tools to bond with the utmost efficiency.

With extensive experience helping manufacturing centers prevent hundreds of thousands of dollars of loss, which can be attributed to ruined chips and reliability issues due to poor wire bonds, SemiGen experts are proficient with developing repeatable and value-added processes. This tech brief details some of the specific wire-bond concerns associated with small MESA chips, and how our experts have resolved them.

Smaller MESAs and faster processes force new bonding techniques.

Small MESA devices have posed a number of wire-bonding challenges, which have required advancements in wire-bonding technologies and skills. As MESA chip size has shrunk and market forces necessitate faster processes with higher yields, the difficulty around wire bonding MESA devices has only expanded. Overcoming these challenges requires not only the latest in wire-bonding equipment, but the process development know-how, and specially designed tools to bond with the utmost efficiency.

With extensive experience helping manufacturing centers prevent hundreds of thousands of dollars of loss, which can be attributed to ruined chips and reliability issues due to poor wire bonds, SemiGen experts are proficient with developing repeatable and value-added processes. This tech brief details some of the specific wire-bond concerns associated with small MESA chips, and how our experts have resolved them.

Types of Wire-Bonding Technologies

Wire bonding is the technique of electrically and mechanically connecting the minute beam leads from integrated circuit (IC) die to larger packages, or directly to another substrate such as a PCB, with fine wire. Wire bonding is performed on over 40 million ICs every year, and is the dominant form of electrical IC bonding from die to package. Traditionally, 1 mil to 3 mil wire diameters were used but, more recently, sub-1 mil wires are increasingly being used to reduce the capacitive and inductive parasitics on RF integrated circuits (RFICs), monolithic microwave integrated circuits (MMICs), and high-speed digital chips.

A significant number of semiconductor device issues are attributed to wire bond failures. There are several wire bond methods that are employed, depending on the materials, costs, die type, application-specific needs, and customer needs. Among the various types are high-temperature thermocompression, which is largely used on aluminum (Al) wire bonding to Al or gold (Au) pad material. Room-temperature, ultrasonic welding is also used to bond Au and Al wire to Al or Au pad materials. Last of the common wire-bond techniques is thermosonic, which uses a combination of ultrasonic welding and thermocompression, and comprises over 90% of wire bonding.

Wire bonds are typically formed using ball bonds or wedge bonds. However, as the performance demands increase, wire sizes decrease, bond pads become smaller, and bond-pad spacing is reduced, ball bonds are becoming increasingly dominant as the bond-forming method employed. Au wire bonding to Au pads was the original method used when wire bonding was developed, and it is still one of the most common materials used today. Aluminum wedge bonding is also used, as its lower cost appeals to certain applications. Nevertheless, Al wire can only be wedge-bonded and can only be used when there is adequate bond-pad spacing. Copper (Cu) and silver (Ag) bond wire is also used, though they are far less common.

Wire Bond Methods

Wire Bonding

Operating Temperature

Wire 
Materials

Pad 
Materials

Note

Thermocompression

300-500°C

Au

Al, Au

High pressure, no ultrasonic energy

Ultrasonic

25°C

Au, Al

Al, Au

Low pressure in ultrasonic energy

Thermosonic

100-240°C

Au, Cu

Al, Au

Low pressure in ultrasonic energy

 

Challenges of Working with Small MESA Devices

Quoting NASA,“Through the improvement of bonding technology the reliability of wire bonds is increasing, as is our understanding of the failure modes, though they continue to plague new manufacturing lines.” As any reduction in yield, or increase of cost and time associated with rework can have dramatic implications to the end cost of a product, improving yields on manufacturing lines largely comes down to the wire-bonding process success. There are only a few typical wire-bond failure modes that account for the large majority of wire-bond failures. The failures range from bond wires peeling off the bond pad to wire bonds breaking during normal assembly and use.

To learn more tips for increasing yields when wire bonding small MESA chips, download our informative tech brief.

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