CO2 spray cleaning in precision parts production

Cleaning parts and assemblies is an extremely critical stage of production, especially in microtechnology. CO 2 snow jet cleaning is a dry, environmentally friendly method that has proven itself in a wide range of applications. The use of snow-blown technology with in-line capabilities means repeatable high cleanliness levels up to the sub-micron range.

Whether processing microchips, molded interconnect devices (MIDs), or mechanical microparts and components, such as gears, gears and pump cleanliness, are key to the success of microfabrication. Even the smallest particles and / or film residues can cause malfunctions and product failures. Therefore, a very thorough cleaning process is required. The CO 2 snow spray cleaning process can be implemented in a repeatable and efficient manner. Fine carbon dioxide snow removes particulate dirt such as particles, chips, dust, and film residues (such as oil, fat, and processing media) from almost all materials.

CO2 injection

Dry, no residue and temperature Compared with CO 2 dry ice blasting, CO 2 snow blasting uses liquid carbon dioxide as a medium. It is fed by bottles or jars and can be stored indefinitely, which means there is no longer a need to separately manufacture and store dry ice pellets. The softness of the fine snow crystals also ensures that sensitive components and fine structures are cleaned without damaging the substrate.

The "core" of snow-blasting technology is a patented cleaning head, designed as a supersonic two-component annular nozzle. When the fluid carbon dioxide leaves the nozzle, it expands to form a snow-air mixture, forming a core jet. In addition, compressed air is forced into the airbag jet, accelerating the CO 2 snow to supersonic speed. By combining thermal, mechanical and sublimation functions, excellent cleaning results can be achieved.

Thermal function When the blasting agent hits the surface at about -78.5 ° C, the surface is rapidly cooled, and the dirt layer becomes cracked and brittle. The difference in the coefficient of thermal expansion of the material and the soil layer maximizes the results.

Mechanical function The dirt particles are detached from the substrate due to the mechanical effect transmitted to the surface by the CO 2 propellant. The aerodynamics of the carbon dioxide and compressed air jets then blow away the dirt particles.

The sublimation of CO 2 from solid to gas produces a pressure wave. This causes the volume to increase, which supports the first two functions.

As the carbon dioxide changes to the gas phase, the material to be cleaned immediately dries. This offsets the energy-intensive drying process required by traditional wet chemistry methods. No cleaning or rinsing residues remain, ensuring biocompatible products in medical technology components.

Application of dry ice

These advantages of removing ablation residues from LDS-MIDS mean that dry ice cleaning is used in more and more cleaning applications for the production of micro-components. One application is the use of LDS technology (laser direct structuring) to remove ablation residues in MID manufacturing. This process enables circuit layouts to be generated directly on complex three-dimensional carrier structures. The advantages of LDS are: expanded design opportunities, fairly low component size and weight, and faster electronic component changes: this can significantly reduce development and mass production costs. Lasers can also produce more precise structures than traditional processes. Special additives in thermoplastic materials are specific to the manufacture of LDS MID. The laser beam initiates a physical-chemical reaction to activate the additive. It is then decomposed in the polymer matrix in the process and used as a catalyst in subsequent reducing copper plating. During laser structuring, active ablation residues, which are also metallized and therefore may cause problems, remain on the surface. Use CO to remove these residues 2 snow spray clean. Compared to conventional cleaning, such as using ultrasonic waves or high-pressure water jets, the process simultaneously smoothes the rough laser structure. The result is a simplified structure and internal connection system for LDS MIDs, such as wire bonding, mating with unmounted chips, and flip-chip technology. In addition, the cleaning module can be easily integrated directly into the laser structure system.

Non-destructive cleaning

The multifunctional CO 2 snow spray cleaning in MICROCHIP production has also been proven in the classic production of microchips by photolithography. It is used to produce magnetoresistive (MR) sensors for various applications at Sensitec GmbH. TOOICE established CO 2 snow spray technology in the manufacture of 3D microchips for MR sensors as an effective and environmentally friendly alternative to conventional wet chemical cleaning. These usually require an expensive rinsing process using ultrapure media. The CO 2 technology removes so-called fences formed at the edges of conductive paths after metallization. The next structure can then be applied to a silicon wafer.

Since even the smallest residues of the fluid medium can affect the function of the microelectronic component or the adhesion of the protective coating, they need to be removed reliably. CO 2 snow provides an economical, residue-free solution for cleaning and improving the adhesion of protective coatings. At the same time, the method is capable of selectively processing specific parts such as adhesion and contact areas.

This method also provides a solution for microchip packaging for RFID applications. Prior to assembly, semiconductors are placed in special magazines by fixtures. During this process, the robot generates sufficient airflow, which can cause extremely light chips to be lifted from the package. To prevent this, the chip is suppressed by the vacuum applied from the back of the package. To do this, a small hole must be drilled and the residue caused by the drilling must be removed. CO 2 snow jet cleaning is good at this particular process.

TOOICE CO2 cleaning technology

Fences produced by chemical reactions in the photoresist at the edges by sputtering on the conductor path can be effectively and reliably removed by using a dry CO 2 snow spray cleaning process.

Using integrated clean laser material processing 3-D laser removal can make very small, fine cavities and shapes. This type of material processing is used in the computer industry, medical technology, automotive and aerospace industries, and other sectors moving toward miniaturization. Due to shorter processing time and lower labor requirements, this process has considerable economic benefits compared to traditional technologies. This is particularly exemplified in the manufacture of injection molds, electronic and semiconductor shapes, mold inserts, indexable inserts, and molds and prototypes.

Lasers can be used to process various materials such as steel, aluminum, brass, hard metals, ceramics, graphite and boron carbide. During the removal process, very fine residues, such as slag or scale, are produced and then removed by suction. For very fine shapes, especially those with steep walls, accumulated residues can reduce laser efficiency and lead to scrap.

Sauer GmbH | Lasertec for residue removal integrates the CO 2 snow spray cleaning module in its 3-D laser system. These modules can be laser-processed to achieve the required cleaning steps for several hours. In addition to the turntable, workpieces are processed on guided machines equipped with X and Y axes. During the (approximately) 10-minute cleaning interval, the machine is guided to position the workpiece in front of the cleaning head according to a part-specific procedure. This integrated cleaning process can use laser systems to make extremely fine parts or even steep walls up to 90 ° (some materials can reach a depth of 2 mm).

Smoke is often left during laser writing of components such as data matrix codes. Because this contamination can lead to inaccurate identification of the code by the reading device, the use of carbon dioxide snow is key to the success of the process.

Cryogenic cleaning

Micro-cleaning and cleaning in one operation Another application is the simultaneous micro-deburring and cleaning of workpieces, such as gears, gear and pump assemblies, and medical technology components. The deburring effect is first based on the mechanical effects caused by the direct influence of snow crystals on the chip. Second, the burrs are damaged by turbulence, causing bending stress. These processes are instantaneous. Clean and deburr in the shortest possible time and get repeatable results.

Integrated automated cleaning

It is used for CO2 and snow spray cleaning in the chemical industry as a by-product. It is not extracted from fossil fuels, so the cleaned CO 2 saves resources and has no impact on the environment. In contrast to wet chemical cleaning, no chemicals are required, no wastewater is generated, and no solvent treatment is required. Furthermore, this method is significantly more energy efficient, as no energy is required to heat, distill or prepare a cleaning medium or for partial drying. This makes CO 2 cleaning an alternative, which has considerable economic and ecological benefits.