Flip-Chip Leadframe Plating to Prevent Solder Spreading

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Solution Overview

Problem

Existing flip-chip semiconductor package manufacturing techniques result in solder balls or bumps spreading out or collapsing during reflow, leading to a low standoff between the chip and leadframe, which prevents proper filling of the molding compound and creates voids in the finished package.

Innovation Solution

Plating a small area of the leadframe with a metal or alloy and forming an oxide or organometallic layer around it to laterally constrain the solder ball during reflow, maintaining a good standoff distance between the chip and leadframe.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If solder balls are used to create electrical contact between chip pads and leads, then electrical connectivity is achieved, but the solder spreads out during reflow causing low standoff and voids in molding compound

Engineering Contradiction:

Improveelectrical connectivityVSAvoidstandoff distance

Core Design Contradiction:

ReliabilityVSManufacturing precision

Solution Approach 1:

The patent changes the physical state and composition parameters of the solder material by using eutectic alloy composition and controlling reflow temperature profiles to prevent solder spreading while maintaining electrical connectivity and proper standoff distance

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent employs composite solder materials with specific eutectic compositions that combine multiple metal elements to achieve optimal melting characteristics, wetting properties, and resistance to spreading during the reflow process

Inventive Principle:

Principle #40Composite materials

2Reliability

If solder balls collapse during reflow, then electrical contact is formed, but molding compound cannot fill properly creating voids in the package

Engineering Contradiction:

Improveelectrical contactVSAvoidmolding compound filling

Core Design Contradiction:

ReliabilityVSEase of manufacture

Solution Approach 1:

The patent modifies the thermal and compositional parameters of the solder material to control its flow characteristics during reflow, ensuring it remains sufficiently viscous to maintain shape while still forming reliable electrical contacts, thereby enabling proper molding compound filling

Inventive Principle:

Principle #35Parameter changes

3Adaptability or versatility

If lead-free solder paste is used instead of high-lead solder balls, then environmental compliance is achieved, but solder spreading and collapse occurs during reflow

Engineering Contradiction:

Improveenvironmental complianceVSAvoidsolder shape control

Core Design Contradiction:

Adaptability or versatilityVSManufacturing precision

Solution Approach 1:

The patent adjusts the compositional parameters of lead-free solder alloys to achieve eutectic formulations with optimized melting points and rheological properties, allowing environmental compliance while preventing solder spreading and maintaining shape control during reflow

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent develops composite lead-free solder materials with multi-element compositions that provide both environmental compliance and improved flow characteristics, preventing collapse and spreading while ensuring reliable electrical connections

Inventive Principle:

Principle #40Composite materials

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

Prevents solder spreading and maintains a consistent standoff, allowing the molding compound to fill properly and minimizing voids in the package, resulting in improved package quality.

Implementation Method 1

forming an oxide or organometallic layer around it to laterally constrain the solder ball during reflow

Methodology Applied

Scientific EffectOxidation: Oxidation

Implementation Method 2

Plating a small area of the leadframe with a metal or alloy and forming an oxide or organometallic layer around it to laterally constrain the solder ball

Methodology Applied

Scientific EffectPhysical barrier constraint: Physical Containment

Data Source

PatentUS8129229B1Method of manufacturing semiconductor package containing flip-chip arrangement

Publication Date: 2012.03.06 UTAC HEADQUARTERS PTE LTD

AI summary

A metal leadframe to be used in manufacturing a “flip-chip” type semiconductor package is treated to form a metal plated layer in an area to be contacted by a solder ball or bump on the chip. The leadframe is then process further to form an oxide or organometallic layer around the metal plated layer. Pretreating the leadframe in this manner prevents the solder from spreading out during reflow and maintains a good standoff distance between the chip and leadframe. During the molding process, the standoff between the chip and leadframe allows the molding compound to flow freely, preventing voids in the finished package.