Laser Reflow Solder Fillet for HDD Slider-Suspension Interconnects

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Solution Overview

Problem

Conventional soldering techniques in hard disc drive systems face challenges in achieving precise and reliable connections due to inherent trajectory errors and solder ball expansion, leading to inadequate separation between pads and traces, particularly in high-density applications.

Innovation Solution

The method involves plating solder on back pads at the wafer level for precision solder positioning, using a laser for reflow to form ellipsoidal solder protrusions, and applying pressurized nitrogen to control the shaping of molten solder, creating a solder fillet between slider and suspension pads for accurate electrical interconnections.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Manufacturing precision

If conventional solder jetting is used to provide electrical connections, then the process is simple and fast, but trajectory errors and solder ball expansion cause inadequate separation between pads and traces, leading to bridging or open connections

Engineering Contradiction:

Improvesolder placement precisionVSAvoidsolder placement process complexity

Core Design Contradiction:

Manufacturing precisionVSDevice complexity

Solution Approach 1:

Solder posts are formed on the slider pads before the slider is assembled with the suspension assembly. This preliminary formation allows precise positioning and control of solder material before final assembly, eliminating trajectory errors associated with conventional solder jetting during assembly operations.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The conventional mechanical solder jetting process is replaced with a laser-based reflow process. The laser provides precise, contactless heating to melt the solder posts, eliminating mechanical trajectory errors and controlling solder flow through optical energy rather than mechanical impact.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Temperature

If a reflow oven is used to melt solder posts, then uniform heating is achieved, but excessive heat causes heat-related issues and potential damage to sensitive components

Engineering Contradiction:

Improveheating uniformityVSAvoidexcessive heat damage

Core Design Contradiction:

TemperatureVSObject-affected harmful factors

Solution Approach 1:

The conventional thermal reflow oven process is replaced with a laser-based heating system. The laser provides localized, on-demand heating only where needed, eliminating the excessive heat exposure that occurs with oven reflow while maintaining sufficient temperature for solder melting.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

Instead of uniform heating across the entire component surface, the laser applies heat locally and selectively only to the solder posts requiring melting. This localized heating approach ensures precise temperature control and prevents heat-related damage to other sensitive components.

Inventive Principle:

Principle #3Local quality

3Manufacturing precision

If solder posts are formed with high aspect ratio (solder volume to pad area), then precise ellipsoidal shaping is achieved with laser, but the process becomes more complex and requires additional controls

Engineering Contradiction:

Improvesolder protrusion shaping precisionVSAvoidsolder formation process complexity

Core Design Contradiction:

Manufacturing precisionVSDevice complexity

Solution Approach 1:

The solder post aspect ratio is optimized to a specific range that enables effective laser reflow. By controlling the solder material dimensions and geometry parameters during formation, the process achieves precise ellipsoidal shaping while maintaining manageable process complexity.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The complex mechanical processes of shaping and positioning solder material are replaced with laser-based melting and surface tension-driven formation. The laser process naturally forms the desired ellipsoidal shape through optical energy, simplifying the overall process despite the high aspect ratio requirements.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

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 enables precise and reliable solder connections with increased interconnect density, minimizing heat-related issues and preventing bridging or open connections, thereby enhancing the reliability of high-density data storage systems.

Implementation Method 1

applying a laser to the ellipsoidal protrusion to reflow the solder bump

Methodology Applied

Scientific EffectLaser heating: Laser

Implementation Method 2

provide the feed material for a surface tension driven interconnect

Methodology Applied

Scientific EffectSurface tension: Surface Tension

Data Source

PatentUS8947830B1Method of forming electrical connections from solder posts

Publication Date: 2015.02.03 SEAGATE TECH LLC

AI summary

A method for forming an electrical interconnection between a slider pad and a suspension pad that is adjacent to and positioned at an angle relative to the slider pad, which includes the steps of forming a solder bump on a first surface of the slider pad, reshaping the solder bump into a protrusion having an ellipsoidal shape that extends from the slider pad and contacts the suspension pad, and applying a laser to the ellipsoidal protrusion to reflow the solder bump while simultaneously applying a downward pressure to the solder bump in order to form a solder fillet between the slider pad and the suspension pad.