Multi-Shot Laser Reflow for Low-Warpage Package Bonding
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Solution Overview
Problem
The warpage of package substrates due to differing Coefficients of Thermal Expansion (CTE) between device dies and package substrates during solder reflow, leading to cold joints and bump cracks, adversely affecting packaging process yield.
Innovation Solution
A multi-shot laser reflow process using controlled laser shots to selectively reflow solder regions on package components, reducing global heating and minimizing warpage by local heating, ensuring complete solder connection without excessive heating of the substrate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional reflow heating is used to melt solder balls, then solder reflow is achieved, but warpage occurs due to elevated temperatures and CTE mismatch
Solution Approach 1:
The patent applies local quality by using a laser beam to heat only the specific solder region that requires reflow, rather than heating the entire substrate. The laser beam is focused on a localized area containing the solder balls, enabling selective heating that melts the solder while minimizing thermal exposure to the rest of the substrate, thereby reducing warpage caused by CTE mismatch.
Solution Approach 2:
The patent segments the heating process into multiple discrete laser shots or pulses, where each shot targets a specific portion of the solder region. This segmentation allows precise control over the heating zones, enabling different areas to be heated independently according to their specific reflow needs, thus avoiding unnecessary heating of adjacent areas that would contribute to warpage.
2Manufacturing precision
If elevated temperature reflow is applied, then solder melting is achieved, but cold joints and bump cracks occur due to warpage
Solution Approach 1:
By concentrating laser energy precisely on the solder regions requiring reflow, the patent achieves complete solder melting and proper bonding without subjecting the entire substrate to elevated temperatures. This localized heating prevents warpage-induced defects such as cold joints and bump cracks that would otherwise occur with conventional global heating methods.
Solution Approach 2:
The patent replaces the conventional mechanical/convection heating system with a laser-based optical heating system. This substitution enables precise spatial and temporal control of thermal energy delivery, allowing solder reflow to be achieved without the uniform high-temperature exposure that causes warpage and associated defects.
3Temperature
If global heating is used for solder reflow, then uniform heating is achieved, but excessive heating of substrate occurs leading to warpage
Solution Approach 1:
The laser beam is focused to heat only the specific solder regions requiring reflow, creating a localized high-temperature zone while keeping the rest of the substrate at lower temperatures. This selective heating achieves the necessary solder reflow temperature in the target areas without causing excessive heating and energy waste across the entire substrate.
Solution Approach 2:
The patent employs periodic laser pulses or shots to deliver thermal energy to the solder regions. This periodic action allows controlled heating cycles that achieve solder melting while providing intervals for heat dissipation, preventing excessive temperature buildup in the substrate and reducing overall energy consumption.
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
Reduces warpage and eliminates defects like cold joints and solder bridging, achieving consistent solder heights and improved bonding quality.
Implementation Method 1
performing a first laser shot on a first portion of a top surface of a first package component... performing a second laser shot on a second portion of the top surface of the first package component
Implementation Method 2
a first solder region between the first package component and the second package component is reflowed by the first laser shot; a second solder region between the first package component and the second package component is reflowed by the second laser shot
Implementation Method 3
a first solder region between the first package component and the second package component is reflowed by the first laser shot
Implementation Method 4
the first solder region is solidified during the period of time
Data Source
AI summary
A method includes performing a first laser shot on a first portion of a top surface of a first package component. The first package component is over a second package component, and a first solder region between the first package component and the second package component is reflowed by the first laser shot. After the first laser shot, a second laser shot is performed on a second portion of the top surface of the first package component. A second solder region between the first package component and the second package component is reflowed by the second laser shot.