Selective Heating for Flip Chip Solder Reflow Alignment
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Solution Overview
Problem
In flip chip mounting of integrated circuit dies on substrates, the thermal reflow process causes substrate expansion, leading to misalignment, solder bridging shorts, and cold solder joints or opens due to fine pitch metal traces and contraction issues.
Innovation Solution
The implementation of selective heating methods, such as infrared, laser, or radio frequency energy sources, is used to heat the integrated circuit die and conductive terminals to a sufficient temperature for solder reflow without heating the substrate, preventing thermal expansion and ensuring stable solder connections.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If thermal reflow process is used to reflow solder, then solder connections are formed between metal bump conductors and substrate, but substrate expansion causes metal traces to move and solder to form bridging shorts
Solution Approach 1:
The patent segments the heating process into two distinct phases: (1) selective heating of the die and solder bump to melt the solder, and (2) cooling of the entire assembly. This segmentation allows the die and substrate to be heated to different temperature profiles, preventing substrate expansion during the critical solder reflow phase while still achieving proper solder connections.
Solution Approach 2:
The patent applies local quality by heating only specific regions (the die and solder bump area) to the reflow temperature while keeping the substrate at a lower temperature. This localized heating approach ensures that the substrate does not expand and cause trace misalignment, while the solder still melts and forms reliable connections.
2Reliability
If substrate is heated during reflow process, then solder melts and forms connections, but substrate contraction upon cooling causes cold solder joints or opens
Solution Approach 1:
The patent segments the thermal processing into distinct phases with different temperature profiles for different components. The die and substrate are heated to different temperatures during reflow, and cooled at different rates, preventing the substrate from contracting and causing solder joint failures.
Solution Approach 2:
The patent applies preliminary action by pre-heating the die and substrate to different temperature profiles before the solder reflow occurs. The substrate is heated to a lower temperature in advance, preventing it from expanding and contracting during the critical solder connection phase, thereby maintaining dimensional stability.
3Productivity
If conventional thermal reflow is used, then solder connections are formed, but fine pitch substrates experience misalignment and solder bridging shorts
Solution Approach 1:
The patent applies local quality by heating only the die and solder bump regions to the reflow temperature while maintaining the substrate at a lower, stable temperature. This localized heating approach enables fine pitch substrates to be processed without thermal expansion, preventing misalignment and solder bridging while maintaining assembly throughput.
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 approach effectively prevents solder bridging and cracking, enabling reliable fine pitch substrates for flip chip mounting with improved yield and process throughput, reducing costs and maintaining substrate integrity.
Implementation Method 1
selective heating methods, such as infrared, laser, or radio frequency energy sources
Implementation Method 2
selective heating methods, such as infrared, laser, or radio frequency energy sources
Implementation Method 3
selective heating methods, such as infrared, laser, or radio frequency energy sources
Implementation Method 4
heating the integrated circuit die and conductive terminals to a sufficient temperature for solder reflow
Implementation Method 5
heating the integrated circuit die and conductive terminals to a sufficient temperature for solder reflow
Implementation Method 6
causes the solder to melt and reflow, forming an electrical and physical connection
Implementation Method 7
the substrate and the die are subjected to heating. However, as the pitch between the metal traces on the substrate becomes smaller ('fine pitch') with advances in semiconductor processing, problems can arise when the substrate is heated. Substrate expansion can occur
Data Source
AI summary
Methods for assembling metal bump dies. In an embodiment, a method includes providing an integrated circuit die having a plurality of conductive terminals; depositing solder to form solder depositions on the conductive terminals; providing a substrate having a die attach region on a surface for receiving the integrated circuit die, the substrate having a plurality of conductive traces formed in the die attach region; aligning the integrated circuit die and the substrate and bringing the plurality of conductive terminals and the conductive traces into contact, so that the solder depositions physically contact the conductive traces; and selectively heating the integrated circuit die and the conductive terminals to a temperature sufficient to cause the solder depositions to melt and reflow, forming solder connections between the conductive traces on the substrate and the conductive terminals on the integrated circuit die. Various energy sources are disclosed for the selective heating.