IPC-HDBK-4691

Description / Abstract: For the purpose of the initial version of this document, the discussion of adhesives will be limited to liquid, paste and gel materials and closely related film adhesives, which require some form of ‘‘cure’’ mechanism to achieve their full performance. Materials that rely primarily on pressure-sensitive bonds, whether coated on an inert film or not (generically ‘‘tapes’’) will not be addressed at this time. Similarly, though there is much overlap in material chemistry and application, the subcommittee has chosen to defer the discussion of underfill materials at present. Underfill materials are discussed in J-STD-030. Surface mount adhesives are also not addressed in this document. Surface mount adhesives are discussed in IPC-SM-817.

Adhesives, for the purpose of this document, are defined as a material (e.g., epoxy, silicone, urethane, cyanoacrylate, polyimide, etc.) that is applied in an uncured state and subsequently processed (i.e., cured) to form a rigid or rubber-like state.

Processing characteristics and curing mechanisms are dependent on the adhesive chemistries used. The desired performance characteristics of an adhesive are dependent on the application and must be considered when selecting adhesive bonding materials and adhesive bonding processes. Users are urged to consult their suppliers for detailed technical data.

This guide enables a user to select an adhesive based on industry experience and pertinent considerations. It is the responsibility of the user to determine the suitability, via appropriate testing, of the selected adhesive and the application method for a particular end-use application. Adhesive bonds may have several functions depending on the type of application. The most common are to:

• Attach one or more electronic functional devices to a substrate.

• Absorb mechanical stresses that would otherwise compromise electrical (e.g., solder) joints.

• Inhibit corrosion.

• Improve fatigue life of solder joints to leadless packages.

• Inhibit arcing and corona, in particular for high-voltage applications.

• Provide mechanical support and prevent damages due to mechanical shock and vibration.

• Provide a mitigation method for the growth of tin whiskers.

Purpose

The term ‘‘adhesive bonding’’ can be ambiguous and be interpreted to mean many things in various industry assembly processes.

The purpose of this handbook is to assist individuals who must either make choices regarding adhesive bonding or who must work in adhesive bonding operations and also to provide guidelines for the design, selection and application of adhesive bonding as it pertains to electronic assembly only.