Multi-wire interconnection: The impact of the lamination process and the encapsulant properties on the solder joint formation

Abstract

ABSTRACT: Multi-wire designs for photovoltaic modules already proved its advantages in the past. In previous contributions, several multi-wire interconnection approaches were presented, both for back-contact [4] and 2-side contacted cells [4,5]. This paper reports the progress in the woven multi-wire interconnection which enables a combined lamination and soldering process using low-temperature melting point solder alloys. This work focuses on the solder joint formation and aims to correlate the viscoelastic properties of the encapsulant material during lamination with the electrical and visual characterisation of the solder joint. To do so, three analysis techniques are used: electroluminescence (EL) imaging, current-voltage (IV) measurements and a cross-section analysis. The aim is to optimize the lamination process and material selection for optimal solder joint formation. Rheological measurements on the encapsulation polymers revealed the viscosities at various temperatures. Small modules were fabricated and tested. According to the results of these tests, the optimal lamination temperature is around 165 ºC and at which the viscosity of the encapsulant should be at least 7500 Pa∙s. One of the tested encapsulant materials met these requirements and had the best electrical properties according to the EL-imaging and IV-measurements