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Solder Paste Printing and Optimizations for Interconnecting Back Contact CellsJuly 26, 2022 | Narahari S Pujari and Krithika PM, MacDermid Alpha Electronics Solutions
Estimated reading time: 2 minutes
The interdigitated back contact (IBC) is one of the methods to achieve rear contact solar cell interconnection. The contact and interconnection via rear side theoretically achieve higher efficiency by moving all the front contact grids to the rear side of the device. This results in all interconnection structures being located behind the cells, which brings two main advantages. First, there is no frontside shading of the cell by the interconnection ribbons, thus eliminating the need for trading off series resistance, losses for shading losses when using larger interconnection ribbons. Second, a more homogeneous looking frontside of the solar module enhances the aesthetics. This combined increased power yield and improved aesthetics make back-contact modules particularly suited for special applications such as vehicle and building integration.
Out of many ways of interconnecting the IBC cells, busbar stringing, which is similar to conventional tabbing and stringing of two-side contacted cells, is the most common method2. In this technique, the metallization design of the cell contains multiple parallel-printed busbars distributed over the cell, allowing shorter finger length, and ribbon on busbar soldering. This reduces the resistance losses in the metallization compared to the edge stringing. With the advent in multibar bar (MBB) technology, the width of these busbars is also reducing and is down to around 300 to 500 microns. The interconnection can be carried out by either ECA (electrically conductive adhesives) or by using direct ribbon/wire. Both materials have created some challenges. The poor peel strength is often the major issue. The uniform IMC (intermetallic layer), which is characteristic of reliable bond strength, is absent with ECA. The metallization paste used in IBC is low-temperature-curing silver paste. The paste is fired at lower temperature around 500°C or less and deposited on silicon cell. In addition to that, the height of the paste is only about 8-12 micron. Because of this, silver leaching during interconnection is commonly observed. The metallization just comes off during interconnection at high temperature. If used, solder wire, cold solder joints, and solder diffusion through the cell are the major issues. Poor adhesion between cell and ECA, and interconnecting wire, high contact resistance are other common problems. Accordingly, when a circuit or conductive layer or interconnection is formed on a substrate using such conventional pastes, damage to the substrate or failure in reliability of the device may occur. Further, when ECA is used, silver in the ECA is expensive and appears on various restricted chemicals lists due its short supply.
To read this entire paper, which appeared in the July 2022 issue of SMT007 Magazine, click here.
AIM Solder, a leading global manufacturer of solder assembly materials for the electronics industry, is pleased to announce its new NC259FPA Ultrafine No Clean Solder Paste, which it revealed recently during the Productronica Germany trade show.
Real Time with... productronica 2023: Koh Young Discusses Semiconductor and Advanced Packaging Inspection11/27/2023 | Real Time with...productronica
Koh Young’s Harald Eppinger talks about the company’s technology for the semiconductor and advanced packaging market and how they address the challenges introduced by reflective components and micro solder deposits.
HyRel Technologies Attains ITAR Registration, Reinforcing Leadership in Robotic Solder Component Tinning11/27/2023 | HyRel
HyRel Technologies, a global provider of quick turn semiconductor modification solutions, announces the achievement of International Traffic in Arms Regulations (ITAR) registration.
Mek (Marantz Electronics), a leader in Automated Optical Inspection (AOI) solutions, used last weeks’ Productronica show in Munich to proudly introduce the SpectorBOX X series, a modular full 3D AOI system for THT solder joints and THT components.
Productronica 2023 played host to the IPC World Hand Soldering Competition, bringing talented regional solder champions from all over the globe to compete for the title of World Champion. Each competitor was given sixty minutes to assemble a complex printed circuit board with their performance judged in accordance with IPC-A-610 Class 3 criteria. Each competitor’s efforts were rated on the merits of the results achieved, scored on the quality of the assembly process, the electrical functionality of the assembly and the speed at which the assembly was produced.