Materials for Advanced Packaging Larger Chip Packages Pose a Challenge for Encapsulation Materials

Larger, thinner, and more complex: Modern semiconductor packages place high demands on encapsulation materials and are in increasingly high demand. Sumitomo Bakelite therefore plans to significantly expand its production capacity for mold underfill and compression molding materials.

The larger and more complex a semiconductor package becomes, the more important the properties of the materials that protect its delicate structures become. In modern packaging processes, encapsulants must now reliably fill even microscopic gaps, compensate for mechanical stresses, and prevent large or particularly thin packages from deforming during processing.

An announcement by the Japanese specialty chemicals company Sumitomo Bakelite. The manufacturer plans to significantly expand its production capacity for mold underfill (MUF) materials and granules for compression molding. Capacity for MUF materials is expected to roughly double, while capacity for compression molding granules is expected to triple.

Why Modern Semiconductor Packages Require New Encapsulants

Encapsulants must be continuously improved because new requirements arise. One such requirement is the so-called warpage effect: When different materials in a semiconductor package are heated or cooled, they expand to different degrees due to their differing coefficients of thermal expansion. This can lead to mechanical stresses that deform the package and, in the worst-case scenario, damage connections or components.

The impact of this effect is particularly critical in large packages containing multiple chips, thin silicon structures, and a high density of electrical connections. In addition to thermomechanical stability, the flow properties of the encapsulation materials are therefore crucial. They must completely fill even the narrowest gaps without trapping voids.

Mold underfill is one way to ensure the required reliability. In this process, the areas around the solder joints between the chip and the substrate, as well as the package itself, are encapsulated in a single molding process. This allows process steps that are performed separately in other methods to be combined. For this purpose, Sumitomo Bakelite relies on materials from its Sumikon EME product family, which, according to the company, combine good flowability in microscopically small gaps with minimal warpage of the package.

The Interplay of Fillers, Viscosity, and Particle Sizes

Materials for compression molding are also becoming increasingly important for large-area packages and panel-level packaging. In this process, the encapsulant is distributed under pressure in a mold and then cured.

The key factor is the interplay of several material properties. The size of the filler particles affects how well tight structures can be filled. Viscosity determines the flow behavior during the molding process, while the material’s composition can influence, among other things, its thermal expansion and mechanical properties.

By carefully adjusting these parameters, Sumitomo Bakelite aims to cast even large panels uniformly while minimizing package warpage. This is a key requirement for cost-effective mass production, particularly in panel-level packaging, where numerous chips are processed on large-area substrates.

In semiconductor manufacturing, this is not just a matter of reliability: A consistent molding process can also make it easier to handle the packages, reduce scrap, and thus impact profitability.

Reliability Makes Repairs More Difficult

Mold underfill processes sound great from a technical standpoint, but there’s a catch. Increasing integration raises questions about the repairability and recyclability of modern semiconductor packages. Conventional epoxy underfill materials are difficult to remove once they have cured. If chips and substrates are permanently bonded together using mold underfill, it is generally not possible to replace individual defective components within the package.

The properties that ensure mechanical stability and a long service life also make disassembly and reuse more difficult. While there are already efforts to develop reworkable underfill materials, their suitability for highly integrated packages depends on the specific material and manufacturing process. The German manufacturer Hoenle, for example, offers flip-chip underfills that can be removed at temperatures above approximately 150 °C (302 °F).

Similar examples can be found in the field of electric mobility: While some manufacturers design their battery packs so that individual components can be disassembled, others glue or encapsulate cells and other parts. This makes repairs and material-specific disassembly considerably more difficult—a recycling disaster unlike any other.

Henkel Is also Developing Materials to Combat Package Warpage

Of course, work on encapsulation materials for large chip packages isn't limited to Japan or to Sumitomo. The Düsseldorf-based specialty chemicals group Henkel also offers, through its Adhesive Technologies business unit, various underfill and encapsulation materials for high-performance semiconductor packages through its Adhesive Technologies business unit.

One example is Loctite Eccobond LCM 1000AG-1, a liquid material for the compression molding of wafers and panels. Henkel relies on fine filler particles with a maximum particle size of 10 µm. According to the manufacturer, the material is designed to reliably fill even narrow gaps and reduce package warpage by more than 70 percent. Henkel lists additional properties, including curing in the mold within five minutes at 120 °C (248 °F), followed by post-curing at 150 °C (302 °F).

Henkel also offers capillary underfills for flip-chip and 2.5D packages. Unlike mold underfill, the material flows into the narrow gaps between the chip and the substrate due to capillary action. The Loctite Eccobond UF 9000AE product is specifically designed to protect the solder joints of large, highly integrated packages against mechanical and thermal stresses.

The various material approaches demonstrate that no single encapsulation technology is sufficient for advanced packaging. Which formulation is suitable depends, among other things, on the package architecture, the size of the voids to be filled, and the manufacturing process used.

Sumitomo Bakelite Expands Production in Asia

To meet growing demand, Sumitomo Bakelite plans to build new production lines in Suzhou, China, and Singapore. Additional production is scheduled to begin in Singapore at the end of fiscal year 2028 and in Suzhou in fiscal year 2030.

Additional capacity is expected to be added through the planned acquisition of Kyocera's chemicals business. Sumitomo Bakelite had already announced in June 2026 a separate expansion of its production of semiconductor encapsulation materials in Suzhou by about 30 percent.

For the semiconductor industry, this development makes it clear above all that the performance of modern chips does not depend solely on the structures on the silicon. The materials and processes used to connect multiple chips into a functional and reliable package are also becoming increasingly important.