Device Module With Asymmetric Pads To Suppress Chip Tilt
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Solution Overview
Problem
In surface mount technology, the tilting of chips during the reflow process is problematic, leading to issues such as optical axis tilt in optical devices, which affects their optical characteristics, and can compromise bonding reliability when reducing solder amount.
Innovation Solution
A device module design featuring a mounting substrate with pads of varying widths, where one end of the electrode surfaces is bonded to a narrower pad portion and the other end to a wider pad portion, using a conductive bonding agent, to create a gentler solder curvature and reduce tilt.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If solder amount is reduced to improve productivity or reduce cost, then bonding reliability deteriorates due to insufficient solder volume, but increasing solder amount increases cost and process complexity
Solution Approach 1:
The pad structure is designed with non-uniform width along the longitudinal direction, creating different local bonding characteristics. The first pad portion has a narrower width while the second pad portion has a wider width, allowing different regions of the same pad to serve different functions in the bonding process
Solution Approach 2:
The pad geometry is made asymmetric by varying the width in the longitudinal direction. This asymmetric design creates a specific solder flow pattern during reflow that generates a gentler curvature, improving chip orientation control while maintaining reliable bonding with reduced solder volume
2Manufacturing precision
If chip tilt is suppressed to improve optical characteristics, then manufacturing precision requirements increase, but relaxed precision requirements can lead to optical axis tilt
Solution Approach 1:
Different portions of the pad are designed with different widths to create specific local solder distribution patterns. The first pad portion (narrower width) and second pad portion (wider width) create varying solder curvature along the longitudinal direction, which helps control chip tilt during bonding
Solution Approach 2:
The varying pad width design intentionally creates a curved solder surface during reflow instead of a flat surface. This controlled curvature in the solder joint helps accommodate and correct chip tilt, improving optical axis alignment while maintaining manufacturing feasibility
3Area of stationary object
If pad width is increased to improve bonding area, then solder curvature increases causing chip tilt, but reduced pad width decreases bonding reliability
Solution Approach 1:
The pad is designed with spatially varying width characteristics. The first pad portion has a narrower width while the second pad portion has a wider width, creating different local solder wetting and curvature characteristics that collectively reduce overall chip tilt
Solution Approach 2:
The pad structure is segmented into different width portions along the longitudinal direction. This segmentation allows the solder to form different curvature profiles in different regions, with the transition from narrower to wider portions creating a gentler overall curvature that reduces chip tilt
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 effectively suppresses chip tilt, maintains bonding reliability, and ensures optimal optical characteristics by creating a nearly flat or gently tilted solder surface, even with reduced solder amounts.
Implementation Method 1
The bonding agent is provided between the pads and the electrode surfaces. The bonding agent is conductive.
Data Source
AI summary
According to one embodiment, a device module includes a mounting substrate, a device, and a bonding agent. The mounting substrate has a mounting surface and a plurality of pads. The device includes a plurality of electrode surfaces arranged in a first direction. The pad has a first width portion and a second width portion. The first width portion has a width in a second direction orthogonal to the first direction. The second width portion is wider than the first width portion and the electrode surfaces in the second direction. One end portion in the first direction of the electrode surface is bonded to the pad on the first width portion via the bonding agent. The other end portion in the first direction of the electrode surface is bonded to the pad on the second width portion via the bonding agent.