PCB Resin Flow Control Using Repelling Member
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Solution Overview
Problem
In the manufacturing of printed circuit boards for electronic devices like digital cameras, the bonding portions between the electronic components and the printed wiring board can be broken due to mechanical stress or thermal expansion, especially when using downsized components with small pitch lands, leading to insufficient reinforcement by uncured thermosetting resin flowing away from the bonding areas.
Innovation Solution
A method involving a paste containing solder powder and uncured thermosetting resin is applied between the lands of the electronic component and the printed wiring board, with a member having a property to repel uncured thermosetting resin disposed on the board, preventing its flow and ensuring adequate coverage and curing of the resin to reinforce the bonding portions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the bonding portions are made smaller to accommodate downsized electronic components with reduced land pitch, then the electronic component can be downsized and performance improved, but the uncured thermosetting resin flows away from the bonding portions during heating, resulting in insufficient reinforcement
Solution Approach 1:
A repelling member is introduced as an intermediary element between the bonding portions and the uncured thermosetting resin. This member has a surface that repels the resin, creating a barrier that prevents the resin from flowing away during heating while still allowing the bonding portions to be adequately reinforced. The repelling member acts as a mediator that controls resin distribution without directly bonding to the lands.
Solution Approach 2:
The repelling member is disposed only in specific locations - on the printed wiring board or electronic component at areas corresponding to outermost bonding portions. This localized application ensures that resin is retained where it is most needed (at the outermost bonding portions that are most prone to resin loss) without preventing resin flow in areas where bonding is already sufficient.
2Ease of manufacture
If paste containing solder powder and thermosetting resin is heated to solder melting point, then solder bonding occurs and resin curing takes place, but the uncured resin separates from solder and flows to periphery, reducing reinforcement effectiveness
Solution Approach 1:
The repelling member serves as a mediator during the heating process, controlling the interaction between molten solder and uncured resin. By repelling the resin during the critical heating phase when resin fluidity is highest, the member ensures proper resin distribution without interfering with solder bonding, thus maintaining both ease of manufacture and manufacturing precision.
3Area of moving object
If the pitch of lands is reduced to downsize the electronic component, then the component size is reduced, but the bonding portions become smaller and more susceptible to resin flow away
Solution Approach 1:
The repelling member is strategically positioned at outermost bonding portions where resin flow away is most problematic. This localized approach compensates for the reduced size of all bonding portions by providing enhanced resin retention specifically where the smallest bonding portions are most vulnerable to losing reinforcement material.
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 effectively prevents the uncured resin from flowing away, ensuring sufficient reinforcement of the bonding portions, enhancing the reliability and longevity of the printed circuit board by maintaining the electrical and mechanical connection despite mechanical and thermal stresses.
Implementation Method 1
the uncured thermosetting resin with fluidity may not stay around the bonding portions but flow from around the bonding portions
Implementation Method 2
the resin is cured through curing reaction caused when the resin is heated
Implementation Method 3
when the paste is heated to a temperature equal to or higher than a solder melting point, the solder is separated from the thermosetting resin which is uncured
Implementation Method 4
disposing a member on one of the first portion and the second portion, the member having a property to repel the uncured thermosetting resin
Data Source
AI summary
A printed circuit board includes an electronic component including a first base and a plurality of first lands, the first base including a first main surface, the plurality of first lands being disposed around a first portion of the first main surface and spaced from each other, a printed wiring board including a second base and a plurality of second lands, the second base including a second main surface, the plurality of second lands being disposed around a second portion of the second main surface and spaced from each other, bonding portions configured to bond the first lands and the second lands, a resin portion configured to cover the bonding portions and including cured thermosetting resin, and a member having a property to repel uncured thermosetting resin and disposed on one of the first portion and the second portion.