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Product Information Electrical and Electronics Market: High-Specification Underfill Agent with Thermal Resistance and Shock Resistance ThreeBond2274S

For Operational Reliability Support of Portable Devices High-Specification Underfill Agents with Thermal Resistance and Shock Resistance

Nowadays, almost all people old and young have portable devices such as mobile phones, portable game machines, car navigation systems, and smartphones. As a result of this, portable devices are constantly exposed to the risks of being dropped, crushed, submerged in water, or exposed to high and low temperatures or to moisture and dust. They are also required to have instantaneous physical durability against these severe environmental conditions and to operate stably and reliably in such environments.
Among the parts used in these portable devices, surface-mounted chips in particular, such as BGA (Ball Grid Array) and CSP (Chip Size Package), have a low ability to adhere to circuit boards and may be damaged or broken by a slight external force. ThreeBond focused on this problem at an early stage and started the development of underfill agents which penetrate into gaps between the chips and the board to reinforce the chips.

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  • MSDS and Technical Data on TB2274S
  • Application Equipment for TB2200 Series
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"The use of our underfill agents covers the restrictions on mechanical design."

The underfill agents function to absorb physical and thermal shocks between surface-mounted chips and the board.
Generally, to improve physical shock resistance, it is advantageous to decrease the content of inorganic fillers to reduce the elasticity modulus of resin.

To the contrary, to improve thermal shock resistance, it is advantageous to increase the content of inorganic fillers. However, the cured resin is harder and more fragile, and since its elasticity modulus is increased, the physical shock resistance and permeability are degraded.

There have been no underfill agents which have these conflicting characteristics, but ThreeBond 2274S makes it a reality.

Commentator

Toshifumi Kuboyama

Okayama Development Section, Development Department, Research and Development Division

Physical Strength Improved by Reduction of Elasticity Modulus

Fig. 1 Ideal Underfill Agent Determined from SS Curve

At first, we succeeded in chemically providing the agent with flexibility by increasing bonds with a high degree of molecular freedom without deteriorating the original water resistance or the chemical resistance of epoxy resin.

In addition, we were able to ensure the intermolecular flexibility while maintaining the thermal resistance without using a plasticizer, which can easily reduce thermal resistance.
As a result of this, we succeeded in developing a technology for reducing the elasticity modulus while maintaining the high strength, high toughness, and high rigidity as shown in Fig. 1.

The key point of this technology consists in that the elasticity modulus can be freely controlled according to the customer's demand.
In other words, it is possible to cover the restrictions on the customer's mechanical design through the use of the underfill agent.

As a result of the evaluation on customer's actual equipment, it was confirmed that the agent has a shock resistance at least twice as high as that of existing products.

"We performed sufficient molecular design to find the best balance between the structure and composition ratio, and were able to greatly improve the possibility of design by customers." (Kuboyama)

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Thermal Resistance Improved by the Increase of Tg

Fig. 2 Relationship between Tg and Amount of Thermal Expansion
Fig. 3 Points of Stress Concentration During Temperature Cycles - Results of Numerical Analysis

To improve thermal resistance, generally, the content of inorganic fillers, such as silica, is increased. However, this method reduces not only the flexibility of the resin, but also its permeability because its viscosity is increased.

Therefore, we considered that the Tg should be increased considerably to obtain stable properties in the normal working temperature range from -40°C to 85°C.
ThreeBond 2274S has a Tg of approximately 124°C, about 20°C higher than existing products.

Therefore, it shows very stable properties in the above temperature range.
Since it does not contain inorganic fillers, its flexibility and permeability are maintained.

Fig. 2 shows change in amount of thermal expansion with change in Tg. As the Tg increases, the amount of thermal expansion caused by heating is less, and the property values are more stable.
The thermal cycle test of ThreeBond 2274S on actual equipment proved that it had a life of more than 2000 cycles while conventional products were broken after 500 cycles.

As shown in Fig. 3, the numeric analysis indicates that ThreeBond 2274S relieves the stress concentration during temperature cycles and disperses stress over the underfill agents.

Fig. 4 ThreeBond2274S

ThreeBond 2274S (Fig. 4) is a high-specification underfill agent which has the conflicting characteristics of flexibility and thermal resistance.
In addition, these characteristics can be freely controlled according to user's demands.

"It is certain that the demand for portable devices will grow. Our mission is to support reliable portable devices which people of the world can use easily in any environment." (Kuboyama)

Application Equipment for TB2200 Series

Several years ago, it was normal for people to exchange their mobile phones with new models when they began operating poorly.
However, nowadays, it is not recommended to discard products rather than repair them. Therefore, we are focusing on developing repairable underfill agents with which BGA and CSP can be removed from wiring boards.

We are simultaneously developing environmentally-friendly halogen-free underfill agents.

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