Snow for optimal connections

Wire bonding is an established interconnection technique in the semiconductor industry and microelectronics. Clean surfaces tailored to specific requirements are essential for high-quality bonds. (Image source: Bond-IQ)

Snow-jet cleaning is a highly efficient method for removing film-like contaminants - in this case, a fingerprint - and particulate contaminants from printed circuit boards. (Image source: Bond-IQ)

The interaction of the four mechanisms ensures that cleaning is effective and fast, yet gentle at the same time. The automated process, integrated into production, guarantees consistent, reproducible results. (Image source: acp systems)

All flux residues are completely and reliably removed from the printed circuit board without compromising the PCB structure. (Image source: acp systems)

Wire bonding is an established connecting technology in the semiconductor industry and microelectronics. Whether high-quality, long-lasting connections are achieved depends crucially on the cleanliness of the bonding surfaces. The dry and scalable quattroClean snow-jet technology reliably and cost-effectively ensures the required cleanliness and can be automated as needed.

As the standard method for electrical contacting in assembly and interconnection technology, wire bonding has been established for 70 years across a broad spectrum of applications. These range from semiconductor technology, microelectronics, and optical components to automotive, consumer products, MEMS, and industrial sensors, as well as specialized applications such as the bonding of battery cells for electric mobility, cordless tools, and energy storage systems. “Wire bonding is generally divided into three major process groups. Two of these are fine-wire processes, in which - depending on the application - wires made of gold, silver, aluminum, or copper with diameters ranging from 18 to 50 µm are used. The third group involves thick-wire bonding with wire diameters ranging from 100 to 500 µm,” explains Stefan Schmitz, Managing Director of Bond-IQ GmbH. The consulting firm specializing in wire bonding technology is the initiator of the Surf:Guide industry project. The project’s goal is to develop a guideline on the cleanliness and condition of bond surfaces, which will serve as the basis for creating an internationally recognized, industry-standard specification.

Cleanliness - a Critical Factor for Quality

Since the bond formation occurs in the nanometer range for both fine-wire and thick-wire bonding, the metals to be bonded must be brought into an atomic state relative to one another. Accordingly, contaminants or interlayers as small as 5 to 10 µm can already hinder the bonding process. These include, for example, fingerprints, bleeding adhesives, flux residues, outgassing from adhesives and other polymers, dust, oxides, or residues from wet-chemical cleaning processes in particular. “Visually detectable contamination is critical for bonding. If this contamination is no longer visible after cleaning, the bonding surface is usually sufficiently clean. This can generally be determined using a microscope and a visual before-and-after comparison. This alone can increase the success rate three- to fourfold,” explains Stefan Schmitz.

Methods for Cleaning Bonding Surfaces

Traditionally, bonding surfaces are still cleaned using wet chemical processes with solvents or water-based media, which require energy-intensive drying. Plasma cleaning can be used for thin, known, and very specific types of contamination. Laser cleaning represents another alternative. “For very sensitive surfaces, such as those in microelectronics, however, the costs of a laser system and the appropriate laser technology must first be balanced,” explains Stefan Schmitz. “The industry is currently showing interest in quattroClean snow-jet cleaning, as it can also remove more stubborn, encrusted contaminants.”

Dry, targeted, and sustainable cleaning

The scalable and cleanroom-compatible quattroClean snow-jet technology is a dry cleaning process for full-surface and localized applications. The process is suitable for the reproducible removal of particulate contaminants down to the submicrometer range and film-like contaminants down to the nanolayer level. The quattroClean technology uses liquid, recycled, and purified carbon dioxide - sourced from chemical production processes and biomass-based energy generation - as its cleaning medium. It is directed through a flexibly adjustable, wear-free dual-component ring nozzle and expands upon exiting into fine snow crystals, which are concentrated by a separate jet of compressed air and projected at supersonic speed onto the surface to be cleaned. The cleaning effect is based on a combination of thermal, mechanical, solvent, and sublimation effects. Since the crystalline carbon dioxide completely sublimates during the process, the treated surfaces remain dry. Removed contaminants are extracted along with the process gas, preventing recontamination of the surfaces and contamination of the surrounding area. In combination with process gas from Linde, the effective quattroClean process holds the Green Screen certification for cleaners and degreasers from Clean Production Action.

Cleaning Technology for a Wide Range of Applications

The low abrasiveness of the fine snow crystals allows even very sensitive and finely structured surfaces to be cleaned.  quattroClean snow-jet technology  can be applied to a very broad range of applications. Among others, the process is used to remove flux and solder residues from PCBs and PCBAs, removing chemical and particulate contaminants from bond pads, and cleaning battery cells prior to contacting. “The process can be used very efficiently on printed circuit boards, which often have a mixture of organic residues such as grease, fingerprints, flux, or residues from wet chemical cleaning processes. We have also achieved excellent results on semiconductors and on housings that have undergone electroplating or other wet chemical processes,” reports Stefan Schmitz. The relatively simple automation of the cleaning process - and its integration into production lines - also contributes to the ease of use. “This results in two advantages. First, automated cleaning ensures reproducible, uniform results. Second, when cleaning is integrated into the manufacturing process, freshly deposited contaminants can be removed immediately,” Stefan Schmitz adds.

acp systems AG will be exhibiting at Electronica in hall A2, booth 112, the fair will be held from 10th to 13th November 2026 in Munich, Germany.