A review of photovoltaic module technologies for increased performance in tropical climate

The global adoption and use of photovoltaic modules (PVMs) as the main source of energy is the key to realising the UN Millennium Development Goals on Green Energy. The technology – projected to contribute about 20% of world energy supply by 2050, over 60% by 2100 and leading to 50% reduction in global CO2 emissions – is threatened by its poor performance in tropical climate. Such performance discourages its regional acceptance. The magnitude of crucial module performance influencing factors (cell temperature, wind speed and relative humidity) reach critical values of 90 °C, 0.2 m/s and 85%, respectively in tropical climates which negatively impact module performance indices which include power output (PO), power conversion efficiency (PCE) and energy payback time (EPBT). This investigation reviews PVM technologies which include cell, contact and interconnection technologies. It identifies critical technology route(s) with potential to increase operational reliability of PVMs in the tropics when adopted. The cell performance is measured by PO, PCE and EPBT while contacts and interconnections performance is measured by the degree of recombination, shading losses and also the rate of thermo-mechanical degradation. It is found that the mono-crystalline cell has the best PCE of 25% while the Cadmium Telluride (CdTe) cell has the lowest EPBT of 8-months. Results show that the poly-crystalline cell has the largest market share amounting to 54%. The CdTe cell exhibits 0% drop in PCE at high-temperatures and low irradiance operations – demonstrating least affected PO by the conditions. Further results establish that back contacts and back-to-back interconnection technologies produce the least recombination losses and demonstrate absence of shading in addition to possessing longest interconnection fatigue life. Based on these findings, the authors propose a PVM comprising CdTe cell, back contacts and back-to-back interconnection technologies as the technology with latent capacity to produce improved performance in tropical climates

Effect of operating temperature on degradation of solder joints in crystalline silicon photovoltaic modules for improved reliability in hot climates

Accelerated degradation of solder joint interconnections in crystalline silicon photovoltaic (c-Si PV) modules drives the high failure rate of the system operating in elevated temperatures. The phenomenon challenges the thermo-mechanical reliability of the system for hot climatic operations. This study investigates the degradation of solder interconnections in c-Si PV modules for cell temperature rise from 25 °C STC in steps of 1 °C to 120 °C. The degradation is measured using accumulated creep strain energy density (Wacc). Generated Wacc magnitudes are utilised to predict the fatigue life of the module for ambient temperatures ranging from European to hot climates. The ANSYS mechanical package coupled with the IEC 61,215 standard accelerated thermal cycle (ATC) profile is employed in the simulation. The Garofalo creep model is used to model the degradation response of solder while other module component materials are simulated with appropriate material models. Solder degradation is found to increase with every 1 °C cell temperature rise from the STC. Three distinct degradation rates in Pa/°C are observed. Region 1, 25 to 42 °C, is characterised by degradation rate increasing quadratically from 1.53 to 10.03 Pa/°C. The degradation rate in region 2, 43 to 63 °C, is critical with highest constant magnitude of 12.06 Pa/°C. Region 3, 64 to 120 °C, demonstrates lowest degradation rate of logarithmic nature with magnitude 5.47 at the beginning of the region and 2.25 Pa/°C at the end of the region. The module fatigue life, L (in years) is found to decay according to the power function L=721.48T-1.343. The model predicts module life in London and hot climate to be 18.5 and 9 years, respectively. The findings inform on the degradation of c-Si PV module solder interconnections in different operating ambient temperatures and advise on its operational reliability for improved thermo-mechanical design for hot climatic operations

Investigation of the effect of nitrogen and air atmospheres on solder wettability of plasma-treated HASL finish PCBs

Purpose – The purpose of this paper is to evaluate the effect of nitrogen and air atmospheres on the solderability testing of plasma-treated hot air solder level (HASL) finish printed circuit boards (PCBs). Design/methodology/approach – In this paper, the soldering performance of plasma-treated HASL finish PCBs in nitrogen and air atmospheres have been evaluated using the wetting balance technique. The results were compared with the performance of conventionally flux-treated samples soldered in air and nitrogen atmospheres and non-flux treated samples soldered in air. Auger chemical analysis results were also compared with the solderability test results in order to obtain a complete profile of the plasma-treated and non-treated surfaces. Findings – The results of the auger chemical analysis show high organic (carbon) levels in the control samples and a significant drop in organic levels in the plasma-treated samples. The significant drop in the level of carbon leads to a decrease in contact angle and an increase in both surface energy and solder wettability. The results indicate that plasma cleaning of PCBs prior to soldering is a viable alternative to the conventional use of flux. Originality/value – The paper indicates that the soldering performance of plasma-treated PCBs in air and nitrogen atmosphere are comparable. The findings give the motivation for the use of plasma-assisted dry cleaning for fluxless soldering

Modelling evaluation of Garofalo-Arrhenius creep relation for lead-free solder joints in surface mount electronic component assemblies

The use of different sets of values of creep parameter in Garofalo-Arrhenius constitutive creep relation has generated distinct magnitude of creep strain (ɛacc) and strain energy density (ωacc) for the same set of solder joints in electronic assemblies. This study evaluates the effect of the use of four set of values on predicted magnitude of damage (ɛacc, ωacc) and number of cycle to failure ( and ) of two different solder joint geometries. The four set of values, proposed by Lau (2003), Pang et al. (2004), Schubert et al. (2003) and Zhang et al. (2003), are used to generate four hyperbolic sine creep relations. The relations are inputted in Ansys FEM software used to simulate the damage on Sn[3.0–4.0%]Ag[0.5–1.0%]Cu solder joints in flip chip model FC48 D6.3C457DC and resistor model R102. The components are assembled on printed circuit boards; and the relations are characterised by comparing the magnitude of each model simulation output with a reference least value. The assemblies are subjected to accelerated high-temperature cycles utilising IEC standard 60749–25 in parts. It was found that each model produces distinctive magnitude and history of stress, strain, hysteresis loop, ɛacc, ωacc, and with the values of stress and hysteresis loop histories generated using Pang et al. and Schubert et al. models being very close. Characterisation results show that the use of ωacc as input parameter in fatigue life model proposed by Syed 2004 demonstrates higher probability of predicting accurately the damage in resistor solder joints while the use of ɛacc demonstrates higher probability for BGA flip chip solder joints. Based on these results, the authors propose a paradigm for selecting suitable constitutive model(s) for accurate ɛacc, ωacc and Nf prediction whilst suggesting the development of new solder constitutive relations

Effects of inter-metallic compound on high temperature reliability of flip chip interconnects for fine pitch applications

Solder joint is a method widely used to attach electronic chip on substrate. It is a generally knowledge that solder joint contains inter-metallic compound (IMC) at interconnects of solder bump and copper pads. The magnitude of IMC layer thickness impacts reliability of chip level packages. Extensive experimental investigations are conducted, however complementary numerical studies are needed to fully characterise the effects of IMC on high temperature reliability of flip chip (FC) assembly. In this work, thermo-mechanical response of FC lead-free solder joints to accelerated temperature cycle (ATC) is investigated using finite element analysis (FEA) code. The ANAND's model is employed to study the inelastic, nonlinear, rate dependent and visco-plastic behaviour of two models of FC48D6.3C457DC mounted on printed circuit boards (PCBs). While one model consists of conventional joints without IMC, the other is realistic with IMC embedded. In the result analysis based on damage indicators such as induced strain, stress, plastic work and hysteresis, it is found that negative impact of IMC on static structural integrity of solder joint operating at high temperature ambient is nontrivial

High temperature electronics: R&D challenges and trends in materials, packaging and interconnection technology

The development of new high temperature electronics (HTE)/systems is the key to achieving high reliability safety critical operations in aerospace, automotive and well-logging applications. Reliability issues associated with the operation of HTE devices have been shown to account for some of the recent aircraft crashes as well as failures of the electronic control Unit in modern vehicles. The reliability of electronic systems is partly dependent on its operating ambient conditions; and reliability generally decreases in harsh operating conditions. The life expectancy of components and systems is known to reduce exponentially as the operating temperature increases; adversely impacting long-term system reliability. As under-bonnet, aerospace and well-logging applications require the direct exposure of sensors to very harsh conditions – these applications demand new HTE systems which can operate reliably in harsh conditions whilst preserving their properties/functions over long operating periods. The packaging and interconnection of the new HTE systems requires better understanding of the complex interactions between HTE system parameters and specific environmental conditions. The paper presents an overview of HTE research, reviews the trends in materials, component packaging and interconnect technology. The paper also outlines the key challenges in HTE research and the outstanding R&D issues

Empirical modeling of the time-dependent structural build-up of lead-free solder pastes used in the electronics assembly applications

Solder paste is the primary bonding material used in the assembly of surface mount devices in electronics industries. It generally has a flocculated structure, which may break-down on shearing and slowly rebuild at rest. The proper characterization of the time-dependent rheological behaviors of solder pastes is crucial for establishing the relationships between the pastes’ structure and flow behavior and for correlating the physical parameters with paste printing performance. In this paper, we present a novel method that has been developed for characterizing the time-dependent and non-Newtonian rheological behavior of solder pastes and flux mediums as a function of shear rates. The objective of the study reported in this paper was to investigate the thixotropic build-up behavior of solder paste and flux mediums. The stretched exponential model has been used to model the structural changes during the build-up process and to correlate model parameters with the paste printing process. As expected, for solder paste samples, the rate of structural recovery was found dependent on the applied shear rate. The model parameters, such as equilibrium viscosity and characteristic time, have been correlated with the shear-thinning and slumping behaviors of solder paste during the stencil printing process