renewable energy 33
A high level of processing is required for fluid system during installation, end users may realise efficiencies based
components used in UHP semiconductor wafer on a less stringent packaging requirement.
manufacturing operations to minimise corrosion and
particle generation. Small line widths and high device
Cleaning
density drive the need for UHP gas and chemical delivery Each step in the manufacturing process introduces
as any particles carried downstream may contaminate contamination. After each step, therefore, UHP
the wafer, resulting in increased scrap and operating semiconductor components must be cleaned thoroughly
expenses. Substrates employed in solar cell production using organic solvents or alkaline- or acid-based cleaners.
are more tolerant of particles, which is, in part, why Similarly, PV components must be also cleaned during
UHP processing standards are too stringent for PV manufacturing. However, the PV market collectively
manufacturing. acknowledges that UHP semiconductor grade cleaning
A clean processing environment is also critical to is not required for crystalline silicon (c-Si) or thin film
ensure proper adhesion between layers in thin film solar PV technologies, the two most common manufacturing
cells (TFSCs), particularly during the wiring process. methods for producing solar cells. Compared to UHP
Properly rated PV components provide the right level of component cleaning standards, the Swagelok Photovoltaic
contamination control for reliable TFSC production. Process Specification reduces requirements for bath
Safety is a further consideration related to corrosion controls, including resistivity and bacteria levels. Rather
and cleanliness. Certain gases used in PV manufacturing than following today’s stricter UHP purity standards, the
are highly reactive. If component connections corrode Swagelok Photovoltaic Process Specification aligns PV
or otherwise deteriorate, these gases may escape to the component cleaning methods to the purity needs of the
atmosphere as fugitive emissions, creating a potentially market.
dangerous work environment. UHP and PV components undergo a variety of tests
during manufacturing to confirm product cleanliness and
PV Manufacturing Protocols
quality. Component producers are particularly concerned
The Swagelok Photovoltaic Process Specification outlines with verifying the corrosion-resistant properties of the
protocols for stainless steel component design, material chromium-enriched oxide surface layer of stainless
selection, and manufacturing steps that are similar to, steel components. These surfaces are enhanced during
but in some cases less stringent than, those used for manufacturing through electropolishing and passivation
UHP semiconductor components. For example, surface processes that remove surface iron and smooth surfaces.
finish requirements are relaxed in the PV specification. UHP standards typically call for advanced surface
Minimising surface flaws and inclusions within a chemistry analysis techniques to confirm corrosion
component reduces the total wetted surface area, which, resistance. The techniques analyse a series of discrete
in turn, improves purging and moisture removal. While points on a sample. Common testing methods
these characteristics are important to maintain cleanliness include Auger Electron Spectroscopy (AES), Electron
in both semiconductor and PV processes, PV production Spectroscopy for Chemical Analysis (ESCA), and
systems are much more tolerant of small amounts of Secondary Ion Mass Spectroscopy (SIMS). These tests are
possible contamination that may result from less polished complex and are often performed by third-party labs, two
surfaces. factors that add cost to UHP component manufacturing
Under the specification, design promotes clean operations.
operation. Components must be able to be cleaned The Photovoltaic Process Specification drives out those
and purged quickly and easily, generate few particles in added costs by specifying an alternative testing method,
service, and contain minimal areas of entrapment. Sound known as the critical pitting temperature (CPT) test.
component designs are of particular importance in TFSC CPT testing is based on ASTM G150: Standard Test
production, which utilises a continuous manufacturing Method for Electrochemical Critical Pitting Temperature
process. In such an environment, equipment must be of Stainless Steels. It evaluates the entire passivated
very reliable to avoid shutting down the entire line. surface of the sample by stressing a sample’s chromium
Component cleanliness specifications must therefore be oxide surface layer to the point of failure to determine its
commensurate with high reliability. resistance to localised pitting corrosion. The temperature
The areas in which UHP semiconductor and PV at which the surface layer fails is known as the CPT.
component manufacturing protocols differ most notably Because CPT testing analyses the full wetted surface
are during the end stages of the product manufacturing area of a sample, it provides a better indication of how
cycle, including the cleaning, verification and testing, well a component will stand up to a harsh environment
and assembly and packaging steps. In these stages, the compared to surface chemistry analysis techniques. n
practices outlined in the Swagelok Photovoltaic Process
Specification enable suppliers to reduce costs compared to John Baxter is Products and Technology Manager, Swagelok
UHP component manufacturing. The resulting savings Company, Solon, Ohio, USA, and Al Bousetta is Marketing
may be passed on down the supply chain, helping to Manager, Gas Products, Santa Clara, California, USA.
reduce the total cost of solar power generation. Further, Swagelok Company. www.swagelok.com
www.engineerlive.com
Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32  |  Page 33  |  Page 34  |  Page 35  |  Page 36