Semiconductor Package Pad Opening for Solder Ball Bonding
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional circuit boards with SMD and NSMD type solder resist openings face issues such as insufficient bonding area for solder balls, incomplete curing of solder resist layers leading to undercut problems, and challenges in reducing the size of circuit boards due to deep undercuts.
Innovation Solution
A semiconductor package with a protective layer having a new type of opening region, where the inner wall of the through hole includes a contact surface in contact with the pad and a non-contact surface, with a specific ratio of contact surface thickness to pad thickness, and a design that minimizes the horizontal distance of the undercut while ensuring the entire pad surface overlaps vertically with the opening.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the opening region width is smaller than the pad width (SMD type), then the solder resist provides better protection and insulation, but the bonding area for solder balls becomes insufficient
Solution Approach 1:
The solder resist layer is designed with different properties in different regions: in the opening region, the thickness is reduced to expose the pad for solder bonding, while in other regions, the full thickness provides protection and insulation. This local variation in thickness creates the desired differential functionality.
Solution Approach 2:
The solution transitions from a two-dimensional planar opening to a three-dimensional structured opening with varying thickness. The opening region has a thickness less than the pad thickness, creating a stepped structure that simultaneously provides protection, insulation, and adequate bonding area.
2Ease of operation
If the opening region width is larger than the pad width (NSMD type), then the solder resist is spaced apart from the pad allowing better access, but the pad becomes separated from the circuit board and bonding reliability decreases
Solution Approach 1:
The solder resist layer is designed with different properties in different regions: in the opening region, the thickness is reduced to expose the pad for solder bonding, while in other regions, the full thickness provides protection and insulation. This local variation in thickness creates the desired differential functionality.
3Reliability
If conventional SMD type opening region is used, then the solder resist provides protection, but light is not sufficiently transmitted to the lower region during exposure, causing incomplete curing and undercut
Solution Approach 1:
The solder resist layer is designed with different properties in different regions: in the opening region, the thickness is reduced to expose the pad for solder bonding, while in other regions, the full thickness provides protection and insulation. This local variation in thickness creates the desired differential functionality.
Solution Approach 2:
The opening region is pre-formed with reduced thickness before the exposure process. This preliminary structural preparation ensures that light can effectively reach and cure the solder resist in the lower regions during the exposure step, preventing incomplete curing and undercut.
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 design enhances the bonding area for solder balls, reduces the depth of undercuts, improves the flowability of connection parts, and allows for a more compact circuit board design with improved reliability and reduced manufacturing time.
Implementation Method 1
when performing a process of exposing the solder resist layer, there is a problem in that light is not sufficiently transmitted to a lower region of an exposure region of the solder resist layer, and accordingly, the lower region of the exposure region is not sufficiently cured
Data Source
AI summary
A semiconductor package according to an embodiment includes an first insulating layer; a first pad disposed on the first insulating layer; and a first protective layer disposed on the first insulating layer and having a first through hole vertically overlapping the first pad, wherein an inner wall of the first through hole includes a contact surface in contact with a side surface of the first pad, and a non-contact surface located on the contact surface, and wherein a ratio of a thickness of the contact surface to a thickness of the first pad is 1:2 or more and less than 1:1.