Pad-on-via wiring circuit board surface flatness
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Solution Overview
Problem
In the pad-on-via structure of wiring circuit boards, the conductive layer forming the pad portion has a recessed portion, leading to the formation of solder voids when solder bumps are bonded, which decreases the bonding strength.
Innovation Solution
A wiring circuit board design that includes a pad portion on one side of a second insulating layer, with a conductive connection portion connected to the peripheral end portion of the pad and the wiring layer, ensuring surface flatness and high-density arrangement of the pad portion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If a pad-on-via structure is used to achieve high density arrangement of pad portions, then the arrangement density of pad portions is improved, but the surface flatness of the pad portion deteriorates due to recessed portions
Solution Approach 1:
The invention transitions from a conventional pad structure where the pad is formed within a recessed via hole to a structure where the pad portion is formed on the surface of the insulating layer. This dimensional change eliminates the recessed portion problem while maintaining high density arrangement capability through the via structure for electrical connection.
Solution Approach 2:
The invention separates the pad portion formation from the via hole formation. The via hole provides electrical connection through the insulating layer, while the pad portion is independently formed on the insulating layer surface, allowing each component to optimize its function without compromising the other.
2Reliability
If a recessed conductive layer is used to form the pad portion, then the electrical connection through the insulating layer is achieved, but the bonding strength with solder bumps deteriorates due to gap formation
Solution Approach 1:
The pad portion is moved from within the via hole recess to the surface of the insulating layer, creating a flat bonding surface for solder bumps. The electrical connection function is maintained through the via structure, while the bonding function is optimized on the flat surface, eliminating gap formation.
Solution Approach 2:
The invention divides the electrical connection function (performed by the via and conductive connection portion) from the mechanical bonding function (performed by the pad portion on the flat surface). This segmentation allows each component to optimize its respective function without compromise.
Data Source
AI summary
A wiring circuit board includes two insulating layers, a wiring layer, a pad portion, and a conductive connection portion. The wiring layer is on one side in a thickness direction of the first insulating layer, and has a contact portion. The second insulating layer is on one side in the thickness direction of the first insulating layer to cover the wiring layer. The pad portion is on one side in the thickness direction of the second insulating layer. The second insulating layer has a through opening portion and having an opening along at least a part of a peripheral end portion of the pad portion. The contact portion of the wiring layer faces the through opening portion. The conductive connection portion, is connected to at least the peripheral end portion of the pad portion, and the contact portion, and electrically connects the wiring layer to the pad portion.