Solder Bump Height Uniformity via Mask-Mediated Mounting
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing methods for manufacturing printed wiring boards with solder bumps face challenges in achieving uniform bump heights due to deformation and damage of small-diameter solder balls during the alignment process, leading to reliability issues and variations in bump volume and height.
Innovation Solution
A method involving the formation of a solder-resist layer with both small-diameter and large-diameter apertures, where a low-melting metal ball is used in paste form for the large-diameter aperture and as a solid for the small-diameter aperture, allowing for the formation of bumps of consistent height through reflowing, and using a mask and cylinder system to accurately position and mount the balls without deformation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a mask and squeegee are used to align and mount solder balls on joint pads, then the solder balls can be positioned on the pads, but the small-diameter solder balls are deformed and damaged during the alignment process
Solution Approach 1:
The patent introduces a specially designed mask as an intermediary tool that mounts solder balls without direct contact between the squeegee and small-diameter solder balls. The mask holds the solder balls in position during alignment, preventing deformation while maintaining positioning accuracy. This mediator approach allows the squeegee to apply pressure only to the printed wiring board and flux, not directly to the vulnerable solder balls.
2Quantity of substance
If solder paste is printed in all apertures and solder balls are mounted in all apertures, then all joints can be formed, but the bump heights become non-uniform due to deformation of small-diameter solder balls
Solution Approach 1:
The patent applies different materials and processes to different aperture sizes. For small-diameter apertures, only solder balls are used without printed solder paste, while for large-diameter apertures, both solder paste printing and solder ball mounting are performed. This local differentiation ensures that small-diameter bumps achieve uniform heights without the deformation issues that would occur if solder paste and balls were combined in all apertures.
3Device complexity
If the same mounting process is used for both small-diameter and large-diameter apertures, then the process is simple, but the bump heights and volumes vary significantly
Solution Approach 1:
The patent segments the mounting process into two distinct procedures: one for small-diameter apertures (solder ball only, no printed paste) and one for large-diameter apertures (solder paste printing followed by solder ball mounting). This segmentation allows each process to be optimized for its specific aperture type, achieving consistent bump dimensions across different sizes while managing complexity through clear process differentiation.
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 ensures consistent bump heights across varying aperture diameters, enhancing joint reliability between the IC chip and the printed wiring board by preventing deformation and damage during the alignment process, thereby improving the overall quality and reliability of the solder bumps.
Implementation Method 1
forming a solder bump from the solder ball by reflowing
Implementation Method 2
the solder bump and the pad (terminal) of the IC chip are joined together by reflowing
Data Source
AI summary
A method for manufacturing a printed wiring board having a bump. The method includes forming a solder-resist layer having a small-diameter aperture and a large-diameter aperture, each aperture exposing a respective conductive pad of the printed wiring board, and printing a solder paste in the large-diameter aperture in the solder-resist layer, but not printing the solder paste in the small-diameter aperture in the solder resist layer. The method also includes loading a solder ball in each of the large-diameter aperture and the small-diameter aperture using a mask having aperture areas that correspond to the small-diameter aperture and large-diameter aperture of the solder-resist layer, and forming a small-diameter bump from the solder ball in the small-diameter aperture and a large-diameter bump from both the solder paste and the solder ball in the large-diameter aperture.