Application of Sekisui Polyvinyl Alkali (PVB) Resin in Conductive Pastes

In conductive pastes, PVB (polyvinyl butyral) is a key component serving as an organic carrier , primarily acting as a temporary binder and dispersant . It determines the paste's printability, film quality, and the precision and reliability of the final conductive circuitry.

Simply put, its role is like that of a " temporary worker " and an " organizer ":

• During the printing and molding stages, it is responsible for binding conductive particles (such as silver, copper, etc.) and solid powders such as glass powder together to form a paste with suitable viscosity and rheological properties so that it can be accurately printed onto the substrate.
• During the subsequent high-temperature sintering stage, it will completely decompose and volatilize , leaving only pure conductive lines with almost no residue.

A.       The core role of PVB in conductive pastes

effect	Detailed Explanation
Binder​	Provides the necessary adhesion to ensure that the printed paste adheres firmly to the substrate (such as silicon wafers or ceramics) and keeps the conductive particles in a stable shape before sintering, preventing them from collapsing or flowing .
Dispersant​	Adsorbed on the surface of conductive particles, the steric hindrance effect prevents their aggregation, thus keeping the slurry in a uniform and stable dispersion state.
rheology modifiers	It can reduce the thixotropy of the paste , providing better fluidity and making it suitable for precision processes such as screen printing .
Film Former	, a smooth and uniform wet film is formed , which, after drying, forms a "green" layer with a certain strength and flexibility , facilitating subsequent lamination and other operations.

 

B.       How to use PVB?

In actual production, PVB is used in the form of resin powder . The standard process is:

1. Dissolution : Dissolve the PVB powder in a suitable organic solvent .
2. Mixing : Thoroughly mix and stir the PVB solution with conductive metal powder, glass powder, and other additives (plasticizers, dispersants, thixotropic agents, etc.) to form a uniform slurry.
3. Aging : Sometimes the prepared slurry is sealed and left to stand (plasticize) for a period of time to stabilize its properties.
4. Printing and sintering : The paste is printed onto the substrate by means of screen printing or other methods, and then sintered at high temperature. The PVB will be completely burned and decomposed to obtain the final conductive layer.

 

C.       How to choose the right PVB?

When selecting PVB, key parameters such as molecular weight, hydroxyl content, and purity need to be considered comprehensively.

• Molecular weight : directly affects the viscosity of the slurry and the strength of the film.
• High viscosity/high molecular weight : suitable for making thicker film layers (such as LTCC green ceramic tape) or for applications requiring high strength.
• Low viscosity/low molecular weight : suitable for fabricating ultra-thin film layers (such as MLCCs, with a thickness of only 2-5μm ) to obtain finer printed lines.
• The specific choice depends on the process. For example, PVB with a weight-average molecular weight (Mw) of 250,000 to 400,000 is commonly used in the internal electrode paste of MLCC, while some formulations use varieties with a molecular weight of less than 50,000 .
• Hydroxyl content : affects adhesion and dispersibility.
• The hydroxyl content of PVB is typically between 10-25 mol% .
• A higher hydroxyl content can provide stronger adhesion, but it may also affect other rheological properties of the slurry.
• The specific choice needs to strike a balance between adhesion and slurry flowability .
• Purity : In high-end electronic ceramic applications such as MLCCs, extremely high purity is required.
• High-purity PVB must be used to ensure no residue remains after sintering , thus not affecting the electrical performance of electronic components. For example, Sekisui Chemicals' S-LEC series offers high-purity products specifically for this application.

D.       Typical Formulation Reference

The specific dosage of PVB in the slurry varies depending on the formulation. The following are common reference ranges:

• Polymer resin (containing PVB) : 10-20 wt %
• Plasticizer : 5-15 wt %
• Organic solvents : 60-85 wt %

In addition, some patents mention that the proportion of organic adhesives (such as PVB) in a specific formulation can be 10-30% .

E.        Summarize

In summary, PVB plays a crucial "temporary" role in conductive pastes. It ensures the precise fabrication of conductive pastes by providing key functions such as bonding, dispersion, and film formation . Furthermore, it completely disintegrates without leaving any residue in the final product , making it an ideal choice for achieving high-performance conductive circuits.

 

Shanghai Canal distributes Japanese Sekisui Chemicals PVB resin suitable for use in conductive pastes such as silver paste, gold paste, and nickel paste. It has good thermal decomposition properties and meets the requirements for low carbon residue .

https://www.canalchem.com/products/prd-category-004/product-007.html