Printed Wiring Board Slit Design for Solder Joint Strain Reduction
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Solution Overview
Problem
The existing printed wiring boards experience premature rupture of solder joints due to strain caused by temperature cycling, as the standing substrate and parent substrate expand and contract, leading to constant stress on the solder joint.
Innovation Solution
A printed wiring board design where the slit in the parent substrate is dimensioned to be significantly larger than the support and its tolerances, allowing for reduced strain on the solder joint during temperature changes, thereby preventing premature rupture.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If the slit dimension is made equal to the support dimension to ensure precise fit, then the structural stability is improved, but the solder joint reliability deteriorates due to constant strain from thermal expansion
Solution Approach 1:
The patent applies beforehand cushioning by designing the slit with dimensions larger than the support dimensions, creating a gap that accommodates thermal expansion before strain can damage the solder joint. This preventive design allows the substrate to expand and contract without transmitting excessive strain to the solder joint, thereby maintaining solder joint reliability under temperature cycling conditions.
2Reliability
If the slit dimension is increased to reduce strain on the solder joint, then the solder joint reliability is improved, but the manufacturing precision deteriorates due to larger tolerance accumulation
Solution Approach 1:
The patent applies parameter changes by deliberately modifying the slit dimension parameters to be larger than the support dimensions. This parameter adjustment creates a dimensional buffer that reduces strain on the solder joint during thermal cycling. The invention specifies that the slit length and width should exceed the corresponding support dimensions to provide sufficient clearance for thermal expansion while maintaining acceptable manufacturing tolerances.
3Reliability
If the slit dimension is made larger than the support to accommodate thermal expansion, then the solder joint reliability is improved, but the device complexity increases due to additional dimensional considerations
Solution Approach 1:
The patent applies local quality by making the slit dimensions locally larger than the support dimensions only in the specific regions where thermal expansion occurs. This localized dimensional adjustment is focused on the slit geometry rather than the entire substrate, providing the necessary clearance for thermal expansion while minimizing the overall design complexity. The invention specifies particular dimensional relationships for the slit relative to the support without requiring complex design changes throughout the entire device.
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
The design effectively reduces strain on the solder joint, extending its lifespan and preventing premature failure by accommodating the thermal expansion of the substrates without applying excessive rotational force on the joint.
Implementation Method 1
The parent substrate and the standing substrate included in the electronic device disclosed in Japanese Patent Laying-Open No. 2004-153178 expand or contract in accordance with a temperature in use environment
Data Source
AI summary
A first substrate has a slit formed therein, passing through the first substrate from one first primary surface to the other first primary surface opposite the one first primary surface, the first substrate including at least one first electrode. A second substrate has one second primary surface and the other second primary surface opposite the one second primary surface, the second substrate: including a support inserted in the slit so as to intersect with the first substrate; and having at least one second electrode on the support. The first electrode and the second electrode are bonded by a solder. A dimension of the slit in the longitudinal direction is greater than the sum of a design dimension of the support in the longitudinal direction, a maximum design dimension tolerance of the support in the longitudinal direction, and a maximum design dimension tolerance of the slit in the longitudinal direction.