Solder Ball Placement Using Resist Layer and Ball Feeder
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
As ball pitch in semiconductor packages decreases, existing stencil-based systems face challenges in accurately and reliably positioning solder balls due to the need for thinner stencils, which become fragile and prone to wrinkle or tear, making it impractical for fine-pitch arrays with ball diameters less than 50 μm.
Innovation Solution
A method involving a resist layer with openings over contact pads, where flux paste is deposited and solder balls are positioned within these openings using a ball feeder that aligns with the openings, allowing for reflow to form solder bumps, eliminating the need for a stencil and addressing the fragility issues of thin stencils.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If stencil thickness is reduced to accommodate finer ball pitch, then manufacturing precision for fine-pitch arrays is improved, but stencil strength and reliability deteriorate causing wrinkles and tears
Solution Approach 1:
The patent removes the stencil component entirely from the ball placement system. Instead of using a stencil to define opening positions, the invention uses a ball carrier with cavities that directly receive and position solder balls. This extraction eliminates the fundamental contradiction between thin stencil requirements for fine-pitch arrays and the need for sufficient stencil strength.
Solution Approach 2:
The invention replaces the reusable, fragile stencil with a disposable or replaceable ball carrier system. The ball carrier can be easily replaced when worn or damaged, avoiding the need to maintain extremely thin, fragile stencils for fine-pitch applications. This approach trades the longevity of a stencil for the simplicity and robustness of a replaceable ball carrier.
2Manufacturing precision
If stencil thickness is reduced to accommodate finer ball pitch, then manufacturing precision for fine-pitch arrays is improved, but device reliability deteriorates due to fragility
Solution Approach 1:
By removing the stencil from the system entirely, the patent eliminates the reliability issues associated with thin, fragile stencils. The ball carrier system provides a more reliable mechanism for fine-pitch ball placement without suffering from the wrinkle and tear problems that plague thin stencils.
Solution Approach 2:
The ball carrier acts as an intermediary device between the solder ball supply and the substrate. Instead of using a fragile stencil to define positions, the ball carrier's cavities directly hold and transfer solder balls to precise locations, providing a more reliable intermediate step in the ball placement process.
3Adaptability or versatility
If traditional stencil-based systems are used for fine-pitch arrays, then existing process compatibility is maintained, but manufacturing precision and reliability worsen due to stencil fragility
Solution Approach 1:
The patent replaces the mechanical stencil system with a ball carrier system that uses cavities and direct placement mechanics. This substitution maintains adaptability to fine-pitch arrays while achieving superior manufacturing precision by eliminating the fundamental limitations of thin stencils.
Solution Approach 2:
The invention changes the fundamental parameters of the ball placement system by transitioning from a stencil-based approach (where precision is limited by stencil thickness) to a ball carrier approach (where precision is determined by cavity positioning). This parameter change enables fine-pitch ball placement without the constraints of stencil fragility.
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 the accurate placement and formation of solder bumps for ball grid arrays with pitches less than 100 μm without the fragility issues associated with thin stencils, allowing for the production of fine-pitch arrays with solder balls as small as 50 μm in diameter.
Implementation Method 1
forming solder bumps on each of the plurality of contact pads by reflowing the plurality of solder balls in the respective openings
Data Source
AI summary
A system and process for forming a ball grid array on a substrate includes defining a plurality of openings in a resist layer on the substrate, and forming a plurality of openings in the resist layer, each positioned over a contact pad of the substrate. Flux is then deposited in the openings, and solder balls are positioned in each opening with the flux. Solder bumps are formed by reflowing the solder balls in the respective openings. The resist layer is then removed, leaving an array of solder bumps on the substrate. The flux can be deposited by depositing a layer of flux, then removing the flux, except a portion that remains in each opening. Solder balls can be positioned by moving a ball feeder across the resist layer and dropping a solder ball each time an aperture in the ball feeder aligns with an opening in the resist layer.