Application of epoxy solder paste to improve the solder strength of chip soldering

2023-04-23

Application of epoxy solder paste to improve the solder strength of chip soldering

Chip soldering is the process of soldering a chip to a circuit board. Solder strength is the maximum load that the soldered joint can withstand and it is very important for chip soldering.

First, solder strength is critical to ensure the reliability and long-term stability of the board. If the solder strength is insufficient, the solder joint is prone to fracture or loosen, leading to the failure of the board. Especially in some high temperature, high pressure, high vibration and other harsh environments, the importance of the solder strength is more obvious.

NDT X-RAY inspection

Second, the solder strength can also affect the electrical properties of the chip. Parameters such as impedance and capacitance of the solder joint can be affected by the solder strength, which in turn affects the efficiency and stability of the chip.

Therefore, during the chip soldering process, attention must be paid to the issue of solder strength and the selection of appropriate soldering processes and solder materials to ensure that the solder joint has sufficient strength and reliability. At the same time, adequate quality inspection is carried out after welding to ensure that the quality of the welded joints meets the requirements.

Factors affecting chip soldering strength

There are many properties that characterize the strength of a chip weld, including thrust, tensile strength, elongation, Young's modulus, and so on. The one that has the most attention and influence is the thrust force. That is, how much thrust can be used to make the chip from the substrate peel.

The main factors affecting the strength of the solder are

1. the type of solder

Due to the differences in alloy properties, different types of solder has different solder strength performance.

2. pad surface treatment

Commonly used pad surface treatments include OSP, chemical or electroplated gold, silver, nickel, tin plating, etc.. Pad surface treatment will affect the oxidation, wetting and other soldering characteristics, and different metals and different reactions occur between the solder, the final will get different welding effect.

3. Soldering process

Commonly used chip soldering process methods include reflow soldering, hot press welding, hot table, laser welding, etc., the heating time, temperature rise rate varies. At the same time the welding process environmental factors also have an impact on the welding effect, and sometimes even the key impact, such as oxygen concentration.

Real-time feedback temperature profile of pulse hot press welding

Common general laser pulse waveform schematic

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Common reflow profiles for reflow soldering

4. Chip size and pad size

Generally speaking, the larger the chip size, the greater the thrust required to ensure the reliability of the chip. The larger the size of the pad can provide greater thrust, and vice versa. When the chip size is too large relative to the pad size, it is easy to produce the phenomenon of insufficient thrust.

Ways to improve chip solder strength

1. the correct choice of solder, according to the needs of the correct choice of alloy, process, solder size;

2. choose the right pad surface treatment technology, choose a good surface treatment with the solder paste compatibility;

3. the use of bottom filler adhesive, the use of bottom filler adhesive can greatly improve the mechanical connection performance, but should pay attention to the bottom filler adhesive and solder paste flux residue compatibility issues, if the bottom filler adhesive and solder paste flux residue chemical reaction is not conducive to improving reliability;