Twice-Molded Semiconductor Package with Exposed Solder Balls

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Solution Overview

Problem

Traditional semiconductor packaging methods require complex processes to protect the semiconductor die while ensuring electrical connections, often resulting in reliability issues and increased costs due to the need for precise exposure of electrical connections during the molding process.

Innovation Solution

A twice-molded semiconductor package approach where a leadframe array with solder balls is first encapsulated in a molding compound, then the semiconductor die is connected and encapsulated again, allowing for separate manufacturing lines and rapid, cost-effective attachment, with the solder balls being fully encased initially to ensure robust electrical connections.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If traditional single-molding process is used to encase die and leadframe together, then packaging is simplified, but electrical connections cannot be properly exposed and reliability decreases

Engineering Contradiction:

Improveelectrical connection reliabilityVSAvoidpackaging process complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The packaging process is divided into two separate molding operations: first molding the leadframe with solder balls exposed, then molding the die separately and attaching it to the leadframe. This segmentation allows electrical connections to be properly exposed and protected in sequence, resolving the contradiction between reliability and process complexity.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The leadframe is pre-molded with solder balls attached and exposed before the die is attached. This preliminary action ensures that electrical connections are prepared and protected in advance, improving reliability while managing process complexity through structured sequencing.

Inventive Principle:

Principle #10Preliminary action

2Ease of manufacture

If die is attached to leadframe before molding, then electrical connections can be made, but the molding process becomes complex and costly

Engineering Contradiction:

Improvemanufacturing cost and easeVSAvoidpackage reliability

Core Design Contradiction:

Ease of manufactureVSReliability

Solution Approach 1:

Instead of attaching the die to the leadframe before molding, the patent inverts the sequence by first molding the leadframe with solder balls, then attaching the die. This inversion simplifies the molding process and reduces costs while maintaining reliability through proper sequencing of operations.

Inventive Principle:

Principle #13The other way round (Inversion)

3Reliability

If solder balls are exposed during molding, then electrical connections are accessible, but protection of solder balls becomes difficult

Engineering Contradiction:

Improveelectrical connection protectionVSAvoidsolder ball exposure precision

Core Design Contradiction:

ReliabilityVSManufacturing precision

Solution Approach 1:

The molding process is segmented into two stages: first molding protects the solder balls while leaving them exposed for connection, then second molding protects the die and its connections. This segmentation resolves the contradiction by providing protection at appropriate stages without requiring precise exposure control in a single complex molding operation.

Inventive Principle:

Principle #1Segmentation

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 method enhances package reliability and reduces manufacturing costs by allowing for mass production of semiconductor packages with improved electrical connections and reduced failure rates, while enabling various package profiles and exposure configurations as needed.

Implementation Method 1

the leadframe array and solder ball combination is placed in a first mold and encased in a first molding compound

Methodology Applied

Scientific EffectEncapsulation:

Implementation Method 2

Solder balls are then applied to the leadframe array... providing electrical connections so the signals may be received by and sent out from the semiconductor die

Methodology Applied

Scientific EffectElectrical conduction: Conduction (electrical)

Implementation Method 3

After the molding compound is cured...

Methodology Applied

Scientific EffectCuring:

Data Source

PatentUS10204814B1Semiconductor package with individually molded leadframe and die coupled at solder balls

Publication Date: 2019.02.12 STMICROELECTRONICS INT NV

AI summary

According to principles as taught herein, a leadframe array for a semiconductor die is prepared having locations to receive solder balls. Solder balls are then applied to the leadframe array, after which the leadframe array and solder ball combination is placed in a first mold and encased in a first molding compound. After the molding compound is cured, a layer of molding compound is removed to expose the solder balls. After this, a semiconductor die is electrically connected to the exposed solder balls. The combined semiconductor die and leadframe are placed in a second mold, and a second molding compound injected. The second molding compound flows around the semiconductor die and leadframe combination, fully enclosing the electrical connections between the leadframe and the semiconductor die, making the final package a twice-molded configuration. After this, the twice-molded semiconductor package array is cut at the appropriate locations to singulate the packages into individual products.