Photovoltaic Cell Die-Attach Inline Testing via Voltage Drop
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Solution Overview
Problem
Current methods for testing die-attach quality in photovoltaic cell assemblies are too time-consuming and complex for integration into manufacturing lines, making it difficult to identify and discard defective assemblies before they are assembled into modules, especially for concentrator photovoltaic modules which are expensive and costly to replace.
Innovation Solution
A method that uses the temperature sensitivity of the forward voltage of a photovoltaic cell to monitor die-attach quality by injecting a high current pulse and measuring the resulting voltage drop, allowing for direct assessment of the thermal interface between the cell and heat sink without the need for external temperature sensors or calibration, enabling inline testing during manufacturing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If thermal transient testing methods are used to verify die-attach quality, then measurement precision is improved, but testing time and complexity increase significantly
Solution Approach 1:
The invention extracts only the essential measurement elements needed for die-attach quality assessment - specifically the forward voltage measurement at a single temperature point - while eliminating time-consuming calibration procedures and multiple measurement points. This allows rapid testing without sacrificing the core measurement capability.
Solution Approach 2:
The method uses a simplified measurement approach that applies partial action - measuring forward voltage at one temperature point rather than multiple points - which is sufficient to detect die-attach quality issues. The excessive heating current is applied briefly to create a measurable temperature rise, then immediately removed for measurement.
2Measurement precision
If thermal transient testing with calibration is performed, then measurement precision is improved, but device complexity and procedural complexity increase
Solution Approach 1:
The invention removes the complex calibration procedure and external temperature sensor requirements from the testing system. By using the photovoltaic cell's own forward voltage temperature coefficient and eliminating the need for stabilized measurement points, the method drastically simplifies the testing procedure while maintaining measurement capability.
Solution Approach 2:
The photovoltaic cell itself serves as the temperature sensor by utilizing its inherent forward voltage temperature dependence. The cell's electrical characteristics provide the temperature information needed for die-attach assessment, eliminating the need for separate temperature sensing devices and calibration procedures.
3Reliability
If conventional die-attach testing is performed after module assembly, then reliability is improved by catching defects, but loss of time and productivity decrease due to late detection
Solution Approach 1:
The invention enables die-attach quality testing to be performed early in the manufacturing process, before photovoltaic modules are fully assembled. This preliminary testing allows defective assemblies to be identified and discarded before they undergo complex module assembly, preventing waste of subsequent assembly efforts and improving overall manufacturing efficiency.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This method allows for quick and reliable identification of defective die-attach assemblies, preventing their use in module assembly and improving the quality and reliability of photovoltaic cell assemblies and modules by integrating the testing process into the manufacturing line, reducing thermal resistance and process variations.
Implementation Method 1
The LED is then subjected to a short non-destructive heating current. Quickly after removal of the heating current, the measurement current is re-applied and the forward voltage is re-measured
Implementation Method 2
The forward voltage of the LED is first measured using a small low-heating measurement current... The difference in forward voltage before and after application of the heating current and the temperature coefficient of the LED material are then used to determine the temperature rise of the LED
Data Source
AI summary
A method for testing the die-attach quality of a photovoltaic cell assembly, in particular, for electrical inline monitoring of a photovoltaic cell die-attach quality during the manufacturing of a concentrator photovoltaic module, comprises the steps of providing a photovoltaic cell assembly comprising at least one photovoltaic cell, in particular, a concentrator photovoltaic cell, attached to a heat sink, injecting a current into the photovoltaic cell assembly, measuring the voltage across the photovoltaic cell during the current injection, and determining the relative voltage drop over the duration of the current injection, whereby insufficiently bonded photovoltaic cell assemblies can be identified and screened.