A Brief Guide on PV Module Assembly

Posted by Alphaassembly on February 23rd, 2017

PV stands for ‘photovoltaic’ and it pertains to the solar cell module assembly, which is becoming increasingly preferred by electronics manufacturing service providers that use SMT. With PV module assembly, EMS providers can effectively fill capacity and diversify. Solar module assemblies accomplish PV cell stringing using conventional SMT processes and materials. Conventional reflow technologies, fluxes, and solders create electrical interconnects in c-Si and a-Si photovoltaic assembly technology. The increasing need for PV module assembly is attributed to the growing demand for clean energy. Manufacturers of PV products have come up with various types of photovoltaic modules, namely CIGS (copper-indium-gallium selenium), Si (silicon), a-Si (amorphous silicon), and CdTe (cadmium-telluride).

Materials
Fluxes, solder preforms, solder wires, and solder pastes are common materials in the SMT process and they are used in the interconnecting procedure during photovoltaic solar cell module assembly. WEEE and RoHS initiatives are not applicable to the solar industry, so a lot of manufacturers still use tin-lead solder alloys for that procedure. Sn62 and Sn60 are popular choices. Tin and silver alloys are used occasionally, and some manufacturers are experimenting on using tin-silver-copper alloys, like SAC305, to produce solder that is up to one-mil thick.

PV ribbon or tabbing ribbon is an interconnect material that is required throughout PV module assembly. It is made of solder-coated OFHC (oxygen-free high conductivity) copper ribbon, which is considered dead soft. The PV ribbon carries current from every PV cell to the bus, a bigger tabbing ribbon that transfers power from PV cell clusters to the power output or junction box. PV ribbons are either photovoltaic cell interconnect ribbon (stringing ribbon) or bussing ribbon.  Stringing ribbon links individual PV cells to one another while keeping them in a cluster, so they can deliver current to the bussing ribbon, which delivers the current to the junction box of the module.

The assembly process
PV modules are assembled using two basic steps: PV cell interconnect using stringing, and PV module assembly via bussing. Solar cell interconnect or tabbing pertains to the process of linking individual PV cells to a PV module. In this process, a solder-coated tabbing ribbon is dipped into flux or sprayed with it. Flux or solder paste may be printed onto the PV cell in an SMT assembly process, and the no-clean paste is preferred to avoid reliability issues.

Solder reflow is usually applied at the tabbing machine while the ribbon is placed on the substrate. Soldering is performed usually using radiant IR (infrared) energy or with automated soldering irons. Once PV cells are strung together, they are placed on the substrate. Six to 10 rows of cells are soldered or bussed together, resulting in a collector grid before another layer of substrate is applied above the cells. Anti-reflective coating is applied to the top glass before the module is sealed and tested. Once it passes the inspection, the module is framed and tested further using a sun simulator to make sure that it can generate enough power.

About the Author:

Alpha Assembly Solutions Inc. is a premier company engaged in the development and manufacture of high quality electronics assembly materials. Since the year of its inception, way back in 1872, the company has played its role on the frontline of innovation, bringing many first-to-market products to the fore thereby, creating a premier niche for itself in the market.