Dielectric Isolation in HGA Flexure for Solder Shrinkage
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Solution Overview
Problem
The use of solder to connect bonding pads of the transducer to termination pads on the flexure in head gimbal assemblies leads to distortion and potential failure due to shrinkage, causing pitch static angle changes, which are exacerbated by environmental conditions like temperature and humidity variations.
Innovation Solution
A flexure assembly with a stainless steel base layer, a conductive trace layer, a dielectric layer, and a cover layer is designed, where the dielectric layer's thickness is matched with the cover layer in the thinning zone to minimize gimbal distortion, and the dielectric layer isolates trace termination pads from the support island, preventing solder wetting and reducing pitch stiffness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If solder is used to connect bonding pads to termination pads, then electrical connection is achieved, but flexure distortion and solder bond failure occur due to solder shrinkage
Solution Approach 1:
The patent introduces an intermediary structure (the isolated trace termination pad design with dielectric layer) between the solder joint and the flexure body. This intermediary configuration absorbs and isolates the shrinkage forces, preventing them from transmitting to the flexure structure and causing distortion, while still maintaining reliable electrical connection.
Solution Approach 2:
The patent segments the flexure into functionally independent zones by isolating the trace termination pad from the support island using a dielectric layer. This segmentation allows the solder joint area to independently accommodate shrinkage forces without affecting the overall flexure geometry, resolving the contradiction between connection reliability and shape stability.
2Ease of manufacture
If standard layered flexure structure is used, then manufacturing is simplified, but pitch static angle variation occurs due to environmental conditions
Solution Approach 1:
The patent applies local quality changes by introducing a dielectric layer specifically in the region of the trace termination pad to isolate it from the support island. This localized modification maintains the overall simplicity of the layered manufacturing process while locally enhancing stability against environmental variations, preventing unwanted stress transmission that would affect pitch static angle.
3Ease of manufacture
If trace termination pads are not isolated, then manufacturing is simpler, but solder wetting of support island causes additional distortion
Solution Approach 1:
The dielectric layer serves as a protective intermediary between the solder and the support island. During assembly, this intermediary prevents solder from wetting the support island, thereby eliminating the harmful effect of solder-induced distortion while adding minimal complexity to the manufacturing process.
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 minimizes pitch static angle variations during assembly and reduces the adverse effects of environmental changes, ensuring stable head positioning and preventing flexure distortion and solder bond failure.
Implementation Method 1
a dielectric layer, where the dielectric layer's thickness is matched with the cover layer in the thinning zone to minimize gimbal distortion, and the dielectric layer isolates trace termination pads from the support island, preventing solder wetting
Implementation Method 2
One problem that arises during HGA assembly, when solder is used to connect bonding pads of the transducer to the termination pads on the flexure, is that the solder shrinks as it cools and solidifies
Data Source
AI summary
Disclosed is a flexure for a head/gimbal assembly suspension for a disk drive. The flexure comprises a metal base layer that includes two outrigger beams and a support island supported by a pair of beams extending from a flexure tongue. The flexure further comprises: a trace layer that is disposed over the base layer that includes a plurality of conductive traces, each conductive trace having a curved section that terminates in a trace termination pad; and a dielectric layer disposed between the trace and base layers including a portion underlying the trace termination pads and overlying the support island. The support island is supported by the pair of beams extending from the flexure tongue and is sized to fully support the trace termination pads of the conductive traces.