ABF (Ajinomoto Build-up Film) is a thermosetting insulating material used between circuit layers in semiconductor package substrates. Its main components include epoxy resin, a curing agent, and inorganic microparticle fillers. Through specialized resin formulation and film processing, ABF provides electrical insulation, low thermal expansion, and processing characteristics required for semiconductor packaging.
Developed by the Ajinomoto Group, ABF is widely used in substrates for high-performance CPUs and other semiconductor packages. Its manufacturing process can be divided into several main stages: resin varnish preparation, mixing and dispersion, coating, drying, and film finishing.
Ajinomoto has not disclosed its complete industrial formulation or all manufacturing parameters. However, the company has published an overview of the basic production process. The following sections describe the manufacturing stages based on publicly available information.
1. Raw material preparation and formulation
The performance of ABF depends on the resin system and the combination of inorganic fillers. Public information identifies several main material groups:
Epoxy resin: Forms the main resin matrix and participates in the subsequent curing reaction to produce the insulating polymer structure.
Curing agent: Reacts with the epoxy resin and influences the curing process and final material properties.
Inorganic microparticle fillers: Silica is a typical filler identified in research on ABF materials. It can help control thermal expansion and other physical properties.
Solvents and other additives: Used to prepare the resin varnish and adjust material properties according to processing and product requirements.
The proportions and combinations of these materials affect the thermal properties, electrical performance, and processability of the finished film. Ajinomoto's technical information specifically identifies uniform dispersion of organic epoxy resin and inorganic microparticle fillers as an important part of ABF development.
2. Resin varnish preparation and dispersion
The raw materials are combined according to a defined formulation to produce a liquid resin mixture known as varnish.
At this stage, the dispersion of the epoxy resin, curing agent, and inorganic fillers must be controlled. Since organic resins and inorganic particles have different physical properties, achieving a uniform and stable mixture is an important part of ABF manufacturing.
The composition and dispersion state of the varnish affect subsequent coating uniformity, film surface quality, and final insulation performance.
The exact material addition sequence, mixing ratios, dispersion equipment, processing time, and temperature are part of the manufacturing process. Ajinomoto has not published the complete parameters used in its production.
3. Coating and film formation
After varnish preparation, the liquid mixture is processed through a film coating operation to form the insulating layer.
Public product information identifies PET film as the support medium for the ABF resin layer. The general manufacturing sequence includes the following steps:
Support film preparation: A PET (polyethylene terephthalate) film is used as the support medium for coating and subsequent processing.
Resin coating: The varnish is applied evenly to the PET support film to form a resin layer with the specified thickness.
Drying: The coated film passes through a drying process to remove the solvent and form a stable insulating layer.
Coating thickness and surface uniformity must be controlled during production. Drying conditions must also be matched to the resin formulation to obtain the required film properties.
The exact coating speed, oven temperature profile, and drying time are proprietary manufacturing parameters. Complete process data is not publicly available.
4. Protective film lamination and product finishing
After drying, a protective film is applied to the other side of the resin layer to complete the insulating film structure.
According to Ajinomoto Fine-Techno's product information, ABF has a three-layer construction:
PET support film
ABF resin insulating layer
Protective film
The protective film helps protect the resin surface during subsequent handling, storage, and use.
Different ABF products have different performance specifications. The official product range includes GX-92, GX-T31, GZ-41, and GL-102. These grades differ in properties such as surface roughness, coefficient of thermal expansion (CTE), glass transition temperature (Tg), and dielectric loss tangent.
5. Product quality inspection
ABF is used in multilayer semiconductor package substrates, where film quality and processing performance must meet demanding requirements. Quality evaluation is carried out according to the specifications of each product.
The main properties include:
Film thickness and uniformity: The resin layer must meet the specified thickness requirements, with local thickness variations controlled.
Surface quality: The film surface is checked for defects that may affect subsequent lamination and circuit fabrication.
Thermal properties: Relevant parameters include the coefficient of thermal expansion (CTE) and glass transition temperature (Tg).
Electrical properties: Insulation performance and dielectric loss are evaluated against the product specifications.
Processing performance: The material is evaluated for its behavior during lamination, laser processing, and subsequent copper circuit formation.
Specific inspection methods, sampling procedures, and acceptance criteria depend on the product grade and the manufacturer's quality requirements. A general inspection procedure should not be assumed to represent Ajinomoto's actual production standards.
6. Subsequent ABF processing in semiconductor packaging
After manufacturing, ABF is used to build multilayer circuit structures in semiconductor package substrates. These operations are part of downstream substrate fabrication rather than the production of the ABF film itself.
Substrate manufacturers typically use the following processes:
Lamination: The ABF film is applied to the substrate. Heat and pressure are used to bond the resin layer to the substrate surface.
Laser processing: Microvias are formed in the insulating layer to establish electrical connections between circuit layers.
Desmear: Residual resin and other contaminants left by the drilling process are removed before metallization.
Copper metallization: Electroless copper deposition and subsequent electroplating are used to form conductive layers.
Multilayer build-up: Insulating film lamination and circuit fabrication are repeated to form the required multilayer substrate structure.
During downstream lamination and subsequent heat treatment, the ABF resin system undergoes the required curing reactions to form the insulating structure between circuit layers.
ABF manufacturing involves resin formulation, inorganic filler dispersion, and precision film processing. Public information provides an overview of the production route, but the detailed formulation, dispersion conditions, and film formation parameters remain proprietary to the manufacturer.
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