Semiconductor Substrate Thinning via Post-Reflow Grinding
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Solution Overview
Problem
The existing substrate thinning processes for flip-chip applications face challenges in achieving uniform thickness and reducing mechanical stress on substrates, particularly when using grinding methods, which can damage solder bumps and increase the risk of substrate breakage during handling and processing.
Innovation Solution
Integrating the substrate thinning process after the solder bump reflow and dicing steps, allowing for reduced handling of thinned substrates and utilizing a combination of mechanical, chemical, and chemical-mechanical techniques to achieve the desired thickness while minimizing damage to solder bumps.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If substrate thinning is performed before solder bump formation, then handling safety is improved, but solder bump damage occurs during grinding
Solution Approach 1:
The patent applies preliminary action by forming the solder bumps on the substrate before performing the thinning process. This reverses the conventional sequence where thinning occurs first, allowing the substrate to maintain sufficient thickness and structural integrity during handling while still achieving the final thin profile after bump formation. The solder bumps are established on a mechanically sound substrate, preventing damage during the thinning operation.
2Adaptability or versatility
If substrate thickness is reduced to achieve ultra-thin die, then flexibility and thermal performance are improved, but mechanical strength decreases
Solution Approach 1:
The patent performs solder bump formation while the substrate still has sufficient thickness to provide mechanical strength and structural support. Only after the bumps are securely formed does the substrate undergo thinning to achieve the final ultra-thin profile. This sequencing ensures that the mechanical strength required for bump formation and initial handling is present, while the final thin profile provides the desired flexibility and thermal performance.
Solution Approach 2:
The patent provides beforehand cushioning by maintaining greater substrate thickness during the critical bump formation stage. This extra thickness acts as a mechanical cushion that protects both the substrate and the forming solder bumps from damage. The cushioning is temporarily present during manufacturing but is removed in the subsequent thinning process to achieve the final ultra-thin product specifications.
3Productivity
If grinding is used for substrate thinning, then thickness reduction is efficient, but sub-surface damage increases
Solution Approach 1:
The patent introduces an intermediary step of solder bump formation before substrate thinning. This intermediary sequence allows the use of efficient grinding methods for thinning without directly exposing the solder bumps to mechanical damage. The bumps serve as a reference structure that guides the thinning process, and any sub-surface damage occurs in the substrate material rather than in the critical solder bump structures. This intermediary positioning resolves the conflict between efficient material removal and protection of sensitive components.
Data Source
AI summary
In a method according to the present invention, a substrate thinning process is performed on a bumped substrate prior to the ultimate solder reflow process to heal bump defects caused by the substrate thinning process. Concurrently, the risk of substrate breakage is reduced compared to the prior art process since the number of process steps, requiring handling of thinned substrates, is reduced.