Pad-Edge Solder Deposition Patterns for Tin Whisker Mitigation

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Solution Overview

Problem

Current methods for mitigating tin whisker formation in electronic assemblies, such as using conformal coatings or tin-lead solder dipping, are costly, time-consuming, and risk damaging sensitive components, with no industry standards for solder coverage, leading to increased costs and risks of electronic failures.

Innovation Solution

A method and system for depositing solder and adhesives in a pattern of discrete domains that extends across the pad area of a substrate, optimizing coverage to the edge of the pad, using lead to mitigate whisker growth and reducing the need for additional resurfacing processes, thereby lowering costs and production time.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If conformal coatings or tin-lead solder dipping are used to mitigate tin whisker formation, then whisker mitigation is achieved, but costs increase and production time increases

Engineering Contradiction:

Improvewhisker mitigationVSAvoidproduction time

Core Design Contradiction:

ReliabilityVSLoss of time

Solution Approach 1:

The patent applies segmentation by using a stencil with multiple discrete openings to deposit solder paste in specific patterns rather than applying conformal coatings uniformly across the entire surface. This targeted approach achieves whisker mitigation only where needed (on pad surfaces) without requiring time-consuming full-surface coating and curing processes

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent extracts the essential function of whisker mitigation from the broader conformal coating process. By using stencil printing to deposit solder paste directly onto pads, it achieves the protective function without the additional time required for applying and curing conformal coatings over the entire circuit board surface

Inventive Principle:

Principle #2Taking out (Extraction)

2Reliability

If conformal coatings or tin-lead solder dipping are used to mitigate tin whisker formation, then whisker mitigation is achieved, but costs increase

Engineering Contradiction:

Improvewhisker mitigationVSAvoidmanufacturing cost

Core Design Contradiction:

ReliabilityVSEase of manufacture

Solution Approach 1:

The stencil printing process segments the solder deposition into discrete pad locations, achieving whisker mitigation only where required rather than applying expensive conformal coatings or tin-lead solder dipping across the entire board surface, thereby reducing material and processing costs

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent uses inexpensive solder paste deposited through a reusable stencil to achieve whisker mitigation, replacing the need for expensive conformal coatings or tin-lead solder dipping processes. The stencil itself is a relatively low-cost tool compared to the expensive materials and processes it replaces

Inventive Principle:

Principle #27Cheap short-living objects (Disposable)

3Reliability

If tin-lead solder dipping is used to mitigate tin whisker formation, then whisker mitigation is achieved, but risk of damaging sensitive components increases

Engineering Contradiction:

Improvewhisker mitigationVSAvoidcomponent damage risk

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The stencil printing process applies solder paste only to specific pad locations rather than immersing the entire component in molten solder, thereby achieving whisker mitigation on critical pads without exposing sensitive components to the high temperatures and mechanical stresses of solder dipping

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent extracts the whisker mitigation function from the harsh solder dipping process by using stencil printing to deposit solder paste that is then reflowed in a controlled manner, eliminating the need for components to withstand the extreme conditions of molten solder immersion

Inventive Principle:

Principle #2Taking out (Extraction)

4Adaptability or versatility

If no industry standards for solder coverage are established, then manufacturing flexibility is maintained, but costs increase and risk of electronic failures increases

Engineering Contradiction:

Improvemanufacturing flexibilityVSAvoidelectronic failure risk

Core Design Contradiction:

Adaptability or versatilityVSReliability

Solution Approach 1:

The patent applies local quality by using stencil openings of varying sizes and shapes tailored to specific pad requirements. This allows optimization of solder coverage for each pad location based on its specific needs, achieving reliable electrical connections and whisker mitigation without requiring uniform solder coverage standards across all pads

Inventive Principle:

Principle #3Local quality

Data Source

PatentUS11033990B2Low cost approach for depositing solder and adhesives in a pattern for forming electronic assemblies

Publication Date: 2021.06.15 RAYTHEON CO

AI summary

A method for depositing a material to join two surfaces of an electronic assembly includes determining, using dimensions of a pad area of a substrate, a deposition pattern for the material that extends across the pad area of the substrate. The method further includes creating a tool to deposit the material in the deposition pattern that extends across the pad area of the substrate.