PLCC Package Reflector Cup Encapsulant Thermal Stress

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Solution Overview

Problem

The current process for producing plastic leaded chip carrier (PLCC) packages faces issues with thermal expansion mismatches between materials, leading to thermal stress, de-lamination, and potential failure of the electrical connection due to repeated temperature changes.

Innovation Solution

A PLCC package design featuring a domed optical lens made from the same encapsulant material as the encapsulant, which covers the reflector cup on all sides, reducing thermal expansion mismatch issues and incorporating rigid lead frames to minimize movement and maintain electrical connectivity.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If silicone is used as encapsulant material, then cracks are reduced, but optical lens performance deteriorates

Engineering Contradiction:

Improvecrack resistanceVSAvoidoptical lens performance

Core Design Contradiction:

ReliabilityVSIllumination intensity

Solution Approach 1:

The encapsulant is divided into two distinct portions: a first portion (silicone) that contacts the die and reflector cup to provide crack resistance, and a second portion (epoxy or similar material) that forms the optical lens to provide optimal light transmission. This segmentation allows each material to perform its specialized function without compromise.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different regions of the encapsulant are assigned different material properties: the first portion uses soft, pliable silicone for mechanical protection and stress absorption, while the second portion uses harder, optically superior epoxy for light transmission. Each local region has quality optimized for its specific function.

Inventive Principle:

Principle #3Local quality

2Adaptability or versatility

If different materials are used in PLCC package, then functional requirements are met, but thermal stress increases

Engineering Contradiction:

Improvefunctional requirementsVSAvoidthermal stress

Core Design Contradiction:

Adaptability or versatilityVSStress or pressure

Solution Approach 1:

The first and second encapsulant portions are configured to be in direct contact with each other, creating a homogeneous interface that eliminates gaps and reduces thermal stress concentration. The materials work together as an integrated system rather than separate components.

Inventive Principle:

Principle #33Homogeneity

Solution Approach 2:

The encapsulant system uses a composite structure combining silicone and epoxy materials, each contributing their advantageous properties. The silicone provides flexibility and stress absorption, while the epoxy provides structural integrity and optical performance, together creating a system that handles thermal expansion better than either material alone.

Inventive Principle:

Principle #40Composite materials

3Stability of the object's composition

If thermal expansion mismatch occurs, then de-lamination happens, but electrical connectivity is maintained

Engineering Contradiction:

Improvestructural integrityVSAvoidelectrical connectivity

Core Design Contradiction:

Stability of the object's compositionVSReliability

Solution Approach 1:

The soft silicone first portion acts as a cushioning layer between the die and the harder second portion, absorbing thermal expansion stresses before they can propagate to cause de-lamination. This beforehand cushioning prevents stress concentration at critical interfaces.

Inventive Principle:

Principle #11Beforehand cushioning (Prior cushioning)

Solution Approach 2:

The first encapsulant portion (silicone) serves as an intermediary between the die and the second encapsulant portion (epoxy), mediating the thermal stress transfer. Its compliant nature allows it to accommodate differential thermal expansion while maintaining the integrity of the electrical connection.

Inventive Principle:

Principle #24Intermediary (Mediator)

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 significantly reduces thermal stress-related de-lamination and maintains electrical connectivity by minimizing thermal expansion mismatches and stabilizing the reflector cup, ensuring the light source functions consistently under thermal cycling conditions.

Implementation Method 1

Silicone is commonly used as a material to encapsulate a light source in a PLCC because it is soft and pliable. Because silicone is soft and pliable, it is often used to reduce cracks in a PLCC package.

Methodology Applied

Scientific EffectElasticity: Elasticity

Implementation Method 2

A PLCC package design featuring a domed optical lens made from the same encapsulant material as the encapsulant, which covers the reflector cup on all sides

Methodology Applied

Scientific EffectReflection: Reflection

Data Source

PatentUS8101955B2PLCC package with a reflector cup surrounded by an encapsulant

Publication Date: 2012.01.24 BENCH WALK LIGHTING LLC

AI summary

In an embodiment, the invention provides a PLCC package comprising first and second lead frames, a plastic structural body, a light source, an encapsulant, and an optical lens. The first lead frame comprises two tongues and a reflector cup. The first and second lead frames are attached to the plastic structural body. The light source is mounted and electrically connected at the bottom of the inside of the reflector cup. The light source is also electrically connected to the second lead frame by a wire bond. The reflector cup is surrounded on at least four sides by the encapsulant, the encapsulant having a domed portion that functions as the optical lens, the encapsulant being an integral single piece structure.