Laser Thermal Imaging for Flip-Chip Bonding Inspection
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Solution Overview
Problem
Existing methods for electrically connecting semiconductor chips to boards, such as flip-chip mounting, face issues with thermal stresses and poor productivity, and lack a reliable method to inspect bonding success in mass production without daisy chains.
Innovation Solution
An inspection method using a laser reflow process with thermal imaging to capture temperature information, comparing it to pre-stored reference data to determine successful bonding between semiconductor chips and boards.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If mass reflow step is used to bond chips to board, then bonding is achieved, but thermal stresses are caused by heating the board entirely
Solution Approach 1:
The patent applies laser beam irradiation to locally heat only the specific regions where chips need to be bonded to the board, rather than heating the entire board. This localized heating approach achieves the required bonding temperature at the bump locations without subjecting the whole board to high temperatures, thereby reducing thermal stress on the board and other components.
2Reliability
If TCB step is used to bond chips to board, then bonding is achieved, but productivity is poor because it takes time to cool the bonder head
Solution Approach 1:
The patent replaces the mechanical contact-based TCB bonding method with a non-contact laser beam irradiation method. The laser beam delivers energy to melt and reflow the bumps without requiring physical contact between a bonder head and the chips, eliminating the cooling time constraint of mechanical systems and enabling faster, more efficient bonding.
3Measurement precision
If electrical continuity test is conducted to determine bonding success, then bonding quality is assessed, but inspection is not possible for mass-produced products where daisy chains are not incorporated
Solution Approach 1:
The patent utilizes thermal radiation (infrared emission) from the chip and bump regions during laser heating as an inspection mechanism. By capturing and analyzing the thermal radiation patterns and temperature distributions, the system can determine whether bonding is occurring successfully without requiring electrical continuity tests or daisy chain structures, making it applicable to all mass-produced chips regardless of circuit design.
4Productivity
If laser beam is applied to multiple chips simultaneously, then productivity is improved, but temperature control becomes more difficult
Solution Approach 1:
The patent incorporates a thermal radiation detection system that monitors the temperature and thermal patterns of multiple chips during laser beam irradiation. This real-time feedback allows the control system to adjust laser parameters dynamically, ensuring uniform and precise temperature control across all chips being processed simultaneously, thereby maintaining bonding quality while achieving high productivity.
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
Enables efficient and reliable inspection of bonding quality, increasing yield by identifying and reworking defective connections, thus improving productivity and reducing thermal stress.
Implementation Method 1
a laser beam applying step of applying a laser beam to the semiconductor chip from an opposite surface of the semiconductor chip to reflow the bump included in an irradiation range of the workpiece
Implementation Method 2
a temperature information acquiring step of capturing an image of the irradiation range with use of a thermal camera while the laser beam is applied to the semiconductor chip, and acquiring temperature information regarding the semiconductor chip from the captured image
Data Source
AI summary
An inspection method includes applying a laser beam to a semiconductor chip to reflow a bump disposed on a surface of the semiconductor chip and included in an irradiation range of the workpiece, the laser beam being applied from an opposite surface of the semiconductor chip, capturing an image of the irradiation range with use of a thermal camera while the laser beam is applied to the semiconductor chip, and acquiring temperature information regarding the semiconductor chip from the captured image, storing in advance reference temperature information that represents temperature information obtained when the semiconductor chip and the board have normally been bonded to each other by the laser beam applied thereto, and determining whether or not the semiconductor chip and the board have normally been bonded to each other by the laser beam applied thereto, on the basis of the reference temperature information and the temperature information.