CASE STUDY

By Dean Quaderer, Automotive Business Director at L&L Products, Romeo, Michigan

Dispensing technology and curing equipment are helping to reliably seal a new generation of switches.

In many instances, you can't do without switches. Whether they be door openers, in production systems, or in medical devices, safe switches are often in demand. With the help of bonding technology expert CREDIMEX, SCHURTER relies on a systems solution that is comprised of adhesives as well as dispensing and curing equipment from DELO to reliably seal its new generation of switches.

As a leading supplier of electronic components, input systems and complete solutions, SCHURTER develops and produces micro and piezo switches, mechanical push-buttons, and non-contact switches in various configurations. The company sees itself as an innovation leader that also offers smart, sustainable device connectors made from bio-based plastic.

SCHURTER also offers it MSMII switches, which are also constantly being developed and improved. This extremely robust product is designed for harsh indoor and outdoor environments, and is therefore used in sectors such as healthcare, food, automotive, and mechanical engineering. Thanks to its IP67 certification, with which devices prove their dust and water resistance, as well as an ultra-high ESD resistance (contact discharge ±8 KV; air discharge ±15 KV), these switches promise to last for up to 20 million actuations, even under demanding conditions.

Diverse Adhesive Requirements

To achieve the promise of lasting up to 20 million actuations, the inside of the switch must be hermetically sealed. For this purpose, and to achieve the aforementioned ESD resistance, a circuit board made of FR4 must be potted and sealed with adhesives. The exact requirements include the following: superior adhesion to FR4, IP67 certification of the switch, consistent tightness throughout the entire temperature range from -40 °C to +85 °C, high media resistance, and a transparent potting appearance so that color of the push-button is clearly visible and optimum signaling is achieved.

SCHURTER produces its new generation of switches in numerous variants with the goal of meeting a wide range of customer requirements. Therefore, as it relates to production, the bonding solution selected for this process should be easy to automate and suitable for producing quantities in the millions annually.

In order to find the best solution for these diverse requirements, the adhesive specialists at CREDIMEX in Alpnach, Switzerland, subjected several candidate products to a series of tests in their in-house laboratory. SCHURTER also conducted its own adhesive strength tests, which included testing after 15 hours of cold storage at -45 °C, after 15 hours of heat storage at +85 °C, and after a six-fold temperature change from -45 °C to +85 °C and back. Further tests were carried out under heat and humidity. For example, SCHURTER tested strength after 21 days of storage at +40 °C and 55% relative humidity.

Following these tests, CREDIMEX recommended the use of a dual-curing product. Specifically, it is a modified, colorless and solvent-free UV acrylate that achieves a compression shear strength of 9 MPa on FR4 and glass. Additional features include flame protection in accordance with ANSI/UL 94 HB and a secondary curing mechanism with humidity. This is particularly useful for reliable curing in shadowed areas where no light reaches during exposure, as is often the case with sealing applications.

The typical exposure time is three seconds at a wavelength of 400 nm. After this short time, the sealant cures and the entire assembly can be processed further. This also makes it suitable for integration into the new, fully automated production line developed by SCHURTER itself, which also includes the necessary dispensing and curing equipment.

The sealant is dispensed via the DELO-DIV VD600 volumetric dispensing system, which achieves up to 99% dispensing accuracy thanks to its endless piston. This, in turn, makes for clean, drip-free dispensing, regardless of viscosity. The sealant is then cured by two DELOLUX 202 / 400 A1 active air-cooled area lamps with a maximum intensity of 1,000 mW / cm². SCHURTER controls them via a compact DELOLUX pilot A2i PROFINET device, which is also integrated into the production line.

The solution that was chosen met all adhesive and production requirements. As the entire process — from dispensing to sealing, to curing — comes from a single source, SCHURTER also benefits from the fact that the system is so coordinated and functions smoothly. This is another reason why production of this new generation of switches has been running as reliably and efficiently as it has at full speed since start of production in fall 2023.