Heat Sealing Processes

heatsealingHeat Sealing Procedures, Process Parameters, and Guidelines for Plastics Assembling

For heat sealing of plastics, anisotropic and formono-isotropic liquid crystal display (LCD) assembly, heat seal connector (HSC) to printed circuit boards (PCB connectors), front panel displays, or other substrates.

Monosotropic and Anisotropic Connector Application Process

Thermal Press International, a manufacturer of assembly equipment utilizing the application of precise temperature and pressure, has developed a method for bonding connectors to LCDs or PCBs and other substrates. The process utilizes precise temperature and pressure control. This consistently and repeatedly produces high quality, sealed bonds.

A heat sealing connector (HSC) consists of an electrically conductive trace printed on a thin film of polyester (or other material). A thermosetting anisotropic or mono-isotropic adhesive, in which electrically conductive particles are dispersed, is used to bond the connector onto the substrate.

Bonding Parameters

Applying a combination of temperature and pressure activates a thermosetting adhesive common with an HSC. Typically, temperatures of at least 120°C (°F) and pressures of at least 20 kg/cm² (PSI) are applied for a minimum of 5 seconds to bond the HSC to a substrate. Actual production process parameters are unique for each application. A study based on what substrates, connectors, process requirements, and process equipment is required in determining the operating parameters for each application. Once optimum parameters are determined, they rarely need adjustment during the production operations.

Plastic Heat Seal Connector Assembly Procedures

The procedural steps for bonding connectors to a substrate are as follows: Clean substrate and HSC as required. Position HSC either visually (fiducials) or mechanically (tooling holes) aligning traces of a HSC, to traces of a substrate. Bond the HSC to the LCD’s substrate or printed circuit board. Inspect the HSC assembly for trace alignment, electrical continuity, and bond strength.

Trace Alignment

The conductive traces of an HSC can be aligned to traces or pads of a substrate by several methods. Tooling holes through an HSC and/or the substrate can be used in aligning them accurately. If an HSC design does not permit tooling holes, they can be aligned manually. A proper manual alignment can be achieved by adjusting an alignment mechanism on a tooling-fixture while viewing the alignments on a magnified optical vision system monitor. Automated alignments are accomplished using a computer-controlled indexing device that can accurately align them while verifying with a computer-controlled magnified vision system (typically incorporating visual inspection software).

Common Assembly Issues

The HSC assembly process has minimal variables.  Assemblies can be rejected for several reasons and are often related to poor machines or tooling design. Common reasons for rejected connector assemblies include: insufficient connector bond strength, inconsistent bond strength, misalignment, broken or damaged components, and continuity inconsistencies on individual traces.

While rejected assemblies in any production process are virtually unavoidable, HSCs can be bonded onto many substrates with a high rate of success if the following application requirements are met. Never use any HSCs that have been on the shelf past their expiration date. Maintain bonding blade planarity with the sealing area of an HSC. Proper use of an interposer material (separator) aids in maintaining a consistent thermal and pressure dispersion. Apply a minimal amount of contact pressure on glass substrates. Maintain a consistent blade temperature.

Plastic Connector Bonding Machines

The principal requirement for any “plastic heat seal” equipment is the ability of the equipment to repeatedly and consistently apply optimum pressure and temperature onto a bonded area while maintaining planarity of the bonding blade to an HSC and substrate.

A manual arbor press can be used for connectors, but inconsistent pressure and dwell time often create quality control issues. High quality equipment is better suited for the HSC assembly process. With any type of system, planarity of the blade to an HSC or substrate can only be maintained if the machine frame is specifically designed to accommodate thermal and force stresses associated with any heat sealing process.

Avoid using equipment with interposer material (usually silicone rubber) inserted into the sealing / bonding blade itself as the material will degrade when exposed to a hot temperature. The degradation will have a direct effect on the success of the process.


Any machine used for connector sealing must meet planarity requirements that are much more stringent than for any other typical bonding application. The equipment should be designed with the idea of maintaining planarity without the requirement of an interposer material.

At Thermal Press we can demonstrate the ease at which our process and equipment can resolve your most demanding sealing, connector seal, LCD to PCB connector assemblies, or any other bond connector requirements. Our equipment can be used for a multitude of staking and heat sealing post. We can help in engineering, design, prototype development, and manufacturing needs. Thermal Press International can save you dollars on the bottom line.

Contact Us at Thermal Press for all of your Heat Sealing Equipment needs: 925-454-9800