RFID Antenna Resist Layer for Solder Overflow Control
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Solution Overview
Problem
RFID tags used in medical gauze, especially in liquid or high-humidity environments, face issues with antenna corrosion and structural dissolution, leading to variations in electrical characteristics due to improper soldering and printing alignment, which affect the characteristic impedance of the wireless IC element.
Innovation Solution
A wireless IC device with a rectangular base material sheet featuring antenna radiation portions and connection portions, where the resist layer covers the radiation portions but not the connection portions, ensuring the conductive bonding material flows along the connection areas and maintains alignment even if displaced, preventing solder ball formation and impedance mismatches.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the antenna is exposed on the surface of the RFID tag to simplify manufacturing, then the manufacturing process is easier, but the antenna becomes corroded and structural components are dissolved in liquid or high-humidity environments
Solution Approach 1:
The patent applies local quality by selectively coating only the radiation portions of the antenna with a resist material, while leaving the connection portions exposed. This localized protection approach provides environmental resistance where needed (radiation portions) while maintaining ease of connection and manufacturing (connection portions remain accessible). The resist layer 220 is formed to cover the radiation portions 231A and 231B but not the connection portions 232A and 232B, creating different protective qualities in different locations.
2Reliability
If excessive solder is supplied during reflow soldering to ensure adequate connection, then connection reliability improves, but solder overflows and forms ball-shaped solder grains that cause printing misalignment and electrical characteristic variations
Solution Approach 1:
The patent applies preliminary action by pre-forming the resist layer 220 to cover the radiation portions before the reflow soldering process. This pre-established protective structure prevents solder from spreading to areas where it should not go, thereby controlling solder flow paths in advance. The resist layer acts as a barrier that guides solder to remain within the connection portions 232A and 232B, preventing overflow and ball formation even when excessive solder is supplied, thus maintaining printing alignment precision.
3Reliability
If the resist layer is printed to precisely cover only radiation portions, then environmental protection is optimized, but printing misalignment occurs that displaces connection portions and varies electrical characteristics
Solution Approach 1:
The patent applies local quality by designing the resist layer 220 to have different functional zones: it covers the radiation portions 231A and 231B for environmental protection, while deliberately leaving the connection portions 232A and 232B exposed for reliable electrical connection. This localized differentiation resolves the contradiction by providing protection where needed without compromising connection precision, as the connection portions remain accessible and properly positioned without resist interference.
4Reliability
If solder is pressed by the wireless IC element during connection, then electrical connection is achieved, but molten solder contacts the resist layer causing overflow and ball formation
Solution Approach 1:
The patent applies the intermediary principle by using the resist layer 220 as a protective barrier between the molten solder and the radiation portions. The resist material acts as an intermediary that prevents solder from contacting and damaging the resist-coated areas. During reflow soldering, even when solder is pressed by the wireless IC element 250, the resist layer serves as a mediator that contains the solder within the connection portions 232A and 232B, preventing overflow and ball formation while maintaining electrical connection reliability.
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 configuration enhances environmental resistance and maintains consistent electrical characteristics by preventing solder overflow and ensuring accurate connection portion alignment, thus improving communication reliability and preventing accidents like lost surgical gauze.
Implementation Method 1
the antenna needs to be coated with a resist material (a coverlay)... a resist layer 220 is provided on a pair of radiation portions 231A and 231B
Implementation Method 2
when the solder 228 is caused to melt due to reflow soldering used to make the electrical connection... the solder 228 in a molten state comes into contact with the resist layer 220
Data Source
AI summary
A wireless IC device includes a base material sheet having a long-side direction and a short-side direction, an antenna element provided on a surface of the base material sheet and that includes two radiation portions extending in the long side direction with a predetermined gap therebetween and two connection portions located in a gap through which the two radiation portions oppose each other, a wireless IC element connected to the two connection portions via a conductive bonding material, and a resist layer that covers the two radiation portions and does not cover the two connection portions and at least areas adjacent to the connection portions in the short-side direction.