LED Package Test Pad Layout for Reverse Leakage Detection
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current LED packaging processes fail to accurately measure leakage current under reverse bias, leading to reduced reliability and detection of defects, especially due to micro cracks and thermal stress, which can cause package failures in high-reliability applications like automotive headlamps.
Innovation Solution
An LED package structure with multiple test pads and a parallel circuit element, featuring first, second, and third electrical test contacts for measuring the electrical characteristics of both the main LED chip and the parallel circuit secondary element, allowing for accurate detection of leakage current and reliability assessment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a Zener diode is connected in parallel circuit to prevent element damage, then element protection against static electricity is improved, but accurate measurement of leakage current under reverse bias deteriorates
Solution Approach 1:
The invention divides the test contacts into multiple groups: first test contacts for forward bias measurement, second test contacts for reverse bias measurement, and third test contacts for leakage current measurement. This segmentation allows independent measurement paths that do not interfere with each other, enabling accurate leakage current measurement while maintaining element protection through the parallel Zener diode circuit.
Solution Approach 2:
The invention introduces intermediate test contacts and conductive structures that act as mediators between the LED chip electrodes and the measurement instruments. These intermediaries provide dedicated measurement paths that isolate the leakage current measurement from the parallel Zener diode circuit, allowing both protection and accurate measurement to coexist.
2Productivity
If conventional test contacts are used to measure forward voltage and brightness, then photoelectric characteristics are detected, but reverse bias characteristics and micro cracks remain undetected
Solution Approach 1:
The invention designs a multi-functional test contact system where the same package structure supports multiple measurement modes (forward bias, reverse bias, leakage current) through different contact combinations. The first, second, and third test contacts can be used in various combinations to perform different measurements, making the testing system universal and comprehensive without requiring multiple separate test setups.
Solution Approach 2:
The invention adds a new dimension to the measurement capability by introducing reverse bias measurement capability alongside the conventional forward bias measurement. By utilizing the second test contacts specifically configured for reverse bias, the system can detect micro cracks and other defects that are invisible under forward bias conditions, effectively adding a new measurement dimension to the testing process.
3Reliability
If LED chip is packaged with bonding adhesive and wire bonding, then electrical connection is achieved, but micro cracks and film stripping occur due to stress
Solution Approach 1:
The invention performs preliminary stress relief by configuring the test contacts and conductive structures before final packaging completion. The test contact structure is designed to accommodate and distribute bonding stresses uniformly, preventing concentration of stress that would cause micro cracks. The conductive metal layers are arranged to provide mechanical support during the bonding process, reducing the risk of film stripping.
Data Source
AI summary
A package substrate comprises first, second and third electrical test contacts, wherein the package substrate is provided with an upper element plane and a lower SMD electrode plane on two sides. The side edge of the upper element plane is provided with first and second electrodes of the main element and first and second electrodes of the secondary element. The main element of LED chip is electrically connected between the first and second electrodes of the main element, a parallel circuit secondary element is electrically connected between the first and second electrodes of the secondary element. The electrical characteristics of the main element of LED chip and the parallel circuit secondary element are measured through the first, second, and third electrical test contacts when electrically connected.