Printed Wiring Board Solder Bump Height Uniformity
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Solution Overview
Problem
Existing methods for forming solder bumps on printed wiring boards result in inconsistent bump heights due to deformation and damage during the ball arrangement process, leading to quality and reliability issues, especially with high-speed IC chips requiring larger power supply bumps and smaller signal line bumps.
Innovation Solution
A method involving a solder-resist layer with varying aperture sizes for loading metal balls, followed by reflow to form bumps of different heights, and subsequent flattening to ensure uniformity, using a mask and suction device to accurately place balls without deformation, ensuring equal volumes and heights across apertures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a conventional ball arrangement method using a squeegee is used, then the process is simple, but the solder balls are deformed and damaged resulting in inconsistent bump heights
Solution Approach 1:
The patent replaces the mechanical squeegee-based ball arrangement method with a suction-based system. A suction device applies negative pressure through a suction port to hold and position solder balls without mechanical contact, eliminating deformation and damage while achieving precise positioning for consistent bump heights.
Solution Approach 2:
The patent introduces a suction device as an intermediary between the solder balls and the substrate. This intermediary uses negative pressure to transfer and position the balls without direct mechanical contact that would cause deformation, thereby improving ball integrity and bump height consistency.
2Manufacturing precision
If solder balls are loaded without precise positioning, then the loading process is fast, but the bump heights vary due to ball deformation
Solution Approach 1:
The patent replaces mechanical pressing methods with a suction-based positioning system. The suction device holds solder balls in precise positions through negative pressure without mechanical contact, achieving both high positioning precision for uniform bump heights and maintaining loading efficiency.
Solution Approach 2:
The patent controls the negative pressure parameter of the suction device to optimize ball positioning. By adjusting the suction pressure, the system achieves precise ball placement without deformation, ensuring uniform bump heights while maintaining efficient loading speeds.
3Reliability
If different sized solder balls are used for power supply and signal lines, then the electrical requirements are met, but the bump heights become inconsistent
Solution Approach 1:
The patent applies different aperture sizes in the mask for different functional areas: larger apertures for power supply connections requiring larger solder balls, and smaller apertures for signal lines requiring smaller solder balls. The suction device positions each ball type precisely in its designated aperture, ensuring both electrical performance and acceptable bump height uniformity within each category.
Solution Approach 2:
The patent varies the aperture size parameter in the mask according to the electrical requirements of different connection types. This allows optimization of solder ball size for each application while the suction positioning system ensures consistent placement precision, achieving both electrical reliability and manufacturing precision.
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 enhances the mountability and connection reliability of IC chips by maintaining consistent bump heights and volumes, reducing the likelihood of non-connections and improving electrical conductivity.
Implementation Method 1
using a mask and suction device to accurately place balls without deformation
Implementation Method 2
followed by reflow to form bumps of different heights
Data Source
AI summary
A method of manufacturing a printed wiring board with solder bumps includes forming a solder-resist layer having small and large apertures exposing a respective conductive pad of the printed wiring board, loading a solder ball in each of the small and large apertures using a mask with aperture areas corresponding to the apertures of the solder-resist layer, forming a first bump having a first height, from the solder ball in the small aperture, and a second bump having a second height, from the solder ball in the large aperture, the first height being greater than the second height, and pressing a top of the first bump such that the first height becomes substantially the same as the second height. A multilayer printed wiring board includes a solder-resist layer with apertures of differing sizes and solder bumps having substantially equal volumes but a difference in height no greater than 10 μm.