The invisible guardian of electronic packaging is facing challenges, epoxy resin bottom filling glue three major problems

With the development of electronic products in the direction of miniaturization and high performance, epoxy resin underfill is the key material of electronic packaging, and its technical bottleneck has become increasingly prominent.

In today's fast-growing electronics industry, epoxy-based underfill is an indispensable material in the chip packaging process. It flows between the chip and the substrate through capillary action, and can effectively disperse the solder joint stress after curing, improve the structural strength of the chip connection, and resist the influence of external impact and temperature change.

One. Three core technical problems

The thermal expansion coefficient matching problem is the first to bear the brunt. Electronic components are composed of materials with different linear expansion coefficients, and under thermal cycling, thermal stress differences will occur due to different expansion scales.

The CTE of epoxy resin is generally higher than that of other packaging materials. When the temperature changes, stress will be generated at the bonding interface, which may lead to local cracking. CTE mismatch is one of the main causes of solder joint fatigue failure.

The internal stress problem in the curing process can not be ignored. Due to the change of bond length, the adhesive will shrink during curing, and large internal stress will be generated during the process from liquid to complete curing, which will easily lead to bonding failure. This stress may cause cracks in the adhesive layer, adhesive desorption and even failure of the device itself.

Material purity control is also a challenge. Most of the epoxy resin synthesis through the epichlorohydrin ring-opening closed-loop process route, will produce chlorine-containing by-products. Chloride ions can corrode the substrate, leading to bonding failure, and their migration can also affect the optoelectronic properties of electronic devices.

At present, the high-purity low-chlorine epoxy resin market is dominated by foreign companies, and domestic products are still insufficient in terms of purity and quality stability.

II. Common problems in the application process

In the practical application process of underfill, the phenomenon of glue overflow occurs frequently. When the adhesive force of some components in the underfill to the substrate is greater than the cohesive force of the underfill, the resin and the filler will separate, and the resin will precipitate to form an overflow.

Glue spills can contaminate components and can cause the underfill to crack from the edges during aging.

Cavity and air gap problems are equally common. The shape, size, frequency and location of voids are important indicators for evaluating the characteristics of voids, which can lead to a decrease in product reliability. Water vapor is the main cause of bubbles, which may be caused by the water vapor attached to the PCB board after a few hours of SMT, or the adhesive is not fully warmed.

Flowability and filling performance are also a pair of contradictions. Viscosity is the main factor affecting the fluidity of the filling glue, and temperature is an important factor affecting viscosity. High viscosity will lead to slow flow, filling is not full; low viscosity is easy to lead to the production process of glue.

Three. Solution Path and Industry Outlook

Faced with these challenges, materials scientists are seeking solutions in multiple dimensions. In terms of anti-overflow technology, the study found that the introduction of cage silsesquioxane can improve the cohesion of the underfill, so that the components can be better combined during the curing process, thereby inhibiting the overflow.

This cage structure can also stop the development of resin microcrack tip and improve the toughness of epoxy resin system.

Optimizing the hardening recipe and process control is another path. By adjusting the type and amount of curing agent, the curing time and process of epoxy resin can be optimized. The introduction of advanced process control equipment, such as temperature control systems and automated hardening equipment, can ensure that the hardening process is carried out under optimal conditions.

The substrate surface treatment is also effective in improving adhesion. Plasma treatment, chemical cleaning or mechanical polishing of the substrate surface can improve surface roughness and activity and enhance adhesion. Modified epoxy resins can also enhance adhesion to substrates by introducing polar groups or using tackifiers.