Zulki’s PCB Nuggets: Three Die Attach Methods for Microelectronics Manufacturing

Die attach technology is increasingly being applied in PCB hybrid manufacturing (i.e., combining traditional SMT manufacturing with microelectronics) to comply with the requirements of small PCBs, especially rigid, flex, and combination rigid-flex circuit boards. These smaller boards are used in a variety of IoT, wearable, and portable applications.

A growing number of these smaller boards cannot be completely designed to undergo traditional SMT manufacturing. As a result, they must go through highly specialized microelectronics manufacturing that entails wire bonding and die attach, flip chip, and similar technologies.

In an earlier column, I detailed PCB wire bonding. Here, I’ll explain die attach (Figure 1). As the name implies, it’s the process of attaching a chip or die to a package, substrate, rigid or flex circuit, another package, or a die attached to another die.

Figure_1.jpg 

Figure 1: Die attach.

The key point to get across here is that die attachments aren’t the same. There are three different die attach methods—epoxy, eutectic, and solder attach—and each possesses important differences.

The epoxy method could be silver epoxy glass or a polyimide-based material. A fine and extremely precise dispenser very accurately dispenses the epoxy. In this case, the substrate is heated to a higher level of temperature, ranging from room temperature up to 200°C, depending on the type of epoxy used. This temperature allows the epoxy to be properly cured so that it adheres to the substrate to precisely create the joint between the substrate and the die.

Eutectic die attach uses a metal layer made of aluminum or gold. Gold has a very high operating temperature ranging from 230°C to 400°C. A eutectic system is a mixture of chemical compounds or elements that form a single composition, which solidifies at a lower temperature compared to these individual elements. These individual elements have considerably higher individual melting points compared to compounds. The fact that eutectic temperature is more manageable and lower compared to the individual pure elements is at the heart of eutectic bonding.

The third die attach method is solder attach, which is similar to SMT manufacturing or SMT joint creation. Solder attach is a common type of die bonding because of better thermal conductivity of the solder material itself. Depending on the different methodologies listed, there could be an extreme variation of temperatures on the die during the die attach process and operation.

Solder attach is an important concept to dissipate the heat, which is generated from the power device—the bond that efficiently creates the joint. When the solder is attached, it is referred to as soft solder attach. Depending on the alloy used, the melting temperature is lower compared to other methodologies. Alloy used in solder attach can either be tin-lead, which melts at 150°C, or indium, which melts at 220°C.

After die attach is complete, wire bonding is performed to create the joint that connects the die to the substrate. These connections are performed by attaching different wires—gold, aluminum, copper, or in some cases, silver—to the die pads to the solder pads on the board or substrate.

Zulki Khan is the president and founder of NexLogic Technologies Inc.

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2019

Zulki’s PCB Nuggets: Three Die Attach Methods for Microelectronics Manufacturing

06-27-2019

Die attach technology is increasingly being applied in PCB hybrid manufacturing (i.e., combining traditional SMT manufacturing with microelectronics) to comply with the requirements of small PCBs, especially rigid, flex, and combination rigid-flex circuit boards. These smaller boards are used in a variety of IoT, wearable, and portable applications.

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Zulki’s PCB Nuggets: Consider the Integrity of Wire Bonding

06-12-2019

While reliability and integrity can be regarded as synonymous as far as PCB manufacturing with microelectronics assemblies is concerned, the integrity of wire bonding—the methodology of interconnecting the wire to the bond pad—takes on other reliability-associated process qualities. Here are three factors that need to be implemented to create the integrity of wire bonding.

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Zulki’s PCB Nuggets: Avoid PCB Wire-bond Loop Failures

05-30-2019

Today, hybrid PCB manufacturing is making greater inroads into our industry, which is the marriage of traditional SMT manufacturing together with microelectronics and wire bonding. In many cases, the OEM working with EMS providers doesn’t fully understand the nuances of effective wire bonding and related failures.

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PCB Hybrid Manufacturing: Coming Your Way

05-15-2019

Today, PCB manufacturing is rapidly evolving to include SMT as well as microelectronics, such as chip-on-board (CoB) installation, flip-chip assembly, wire bonding, and die attach. SMT merged with microelectronics is also known as hybrid manufacturing. This is occurring because PCBs have begun shrinking at a faster pace in recent years due to the introduction of wearables, IoT devices, and portables demanding smaller circuit boards.

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2014

Tighter Scrutiny Needed for PCB Cleaning Agents

05-13-2014

PCB cleanliness on the assembly floor is now getting more attention, due to tiny residues and contaminants being left on assemblies after new, advanced assembly processes. Cleaning methodologies, testing, analysis, and special chemistries are being taken to a new level to assure customers of ultraclean boards to avoid costly latent issues.

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Zulki's PCB Nuggets: Tighter Scrutiny Needed for PCB Cleaning Agents

05-13-2014

PCB cleanliness on the assembly floor is now getting more attention, due to tiny residues and contaminants being left on assemblies after new, advanced assembly processes. Cleaning methodologies, testing, analysis, and special chemistries are being taken to a new level to assure customers of ultraclean boards to avoid costly latent issues.

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Uncovering Assembly Problems of High-Speed PCBs

03-12-2014

The high-speed board may be perfect when it comes to BGA assembly. All the balls properly collapse; all the thermal profiles are accurately determined and performed. All soak temperatures, pre-heat, soak, and cool-off periods fall within manufacturer limits and ranges. Yet, this high-speed board fails at high speed at the time of system functional level testing in the system.

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Zulki's PCB Nuggets: Uncovering Assembly Problems of High-Speed PCBs

03-12-2014

The high-speed board may be perfect when it comes to BGA assembly. All the balls properly collapse; all the thermal profiles are accurately determined and performed. All soak temperatures, pre-heat, soak, and cool-off periods fall within manufacturer limits and ranges. Yet, this high-speed board fails at high speed at the time of system functional level testing in the system.

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EMS Discovers Mature IC Technologies

01-14-2014

Columnist Zulki Khan asks, "Did you know that really new, up-to-the-moment PCB technologies are nesting on the doorstep of PCB assemblers?" In fact, he says some of these technologies are very mature, but they're completely new to the assembly side of things.

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Zulki's PCB Nuggets: EMS Discovers Mature IC Technologies

01-14-2014

Columnist Zulki Khan asks, "Did you know that really new, up-to-the-moment PCB technologies are nesting on the doorstep of PCB assemblers?" In fact, he says some of these technologies are very mature, but they're completely new to the assembly side of things.

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2013

Another Look at AOI

11-13-2013

PCB inspection is taking on greater significance as boards and packaging become increasingly smaller, with greater functionality. Automated optical inspection (AOI) and its backup associate, X-ray, team up to catch a variety of board assembly problems. But it's AOI that's at the forefront of this process.

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Zulki's PCB Nuggets: Another Look at AOI

11-13-2013

PCB inspection is taking on greater significance as boards and packaging become increasingly smaller, with greater functionality. Automated optical inspection (AOI) and its backup associate, X-ray, team up to catch a variety of board assembly problems. But it's AOI that's at the forefront of this process.

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Zulki's PCB Nuggets: ECOs Reviewed - The Importance of Accuracy

09-11-2013

Designers can perfectly layout a design and, in theory, follow written specifications to the letter, but when one factors in the practicality of that design, virtually everything associated with it has its limitations--ranging from the material used to make the board to assembly, machine tolerances, and process limitations.

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