PCB Through Hole Solder Sealing Prevents Underfiller Overflow

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Solution Overview

Problem

Existing methods for manufacturing printed circuit boards face challenges with underfiller overflow and spread due to through holes in the printed wiring board, requiring complex sealing processes and additional materials, which can compromise junction reliability and electrical characteristics.

Innovation Solution

A method involving coating the surfaces of electrode pads and through holes on the printed wiring board with a bonding material, mounting a semiconductor package, and filling the space between the package and the board with a filler material, using solder to seal and fill the through holes, thereby preventing underfiller overflow and spread.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Object-affected harmful factors

If through holes are sealed with a sealing material on the back surface, then underfiller outflow to the back surface is prevented, but the manufacturing process becomes complex

Engineering Contradiction:

Improveunderfiller outflowVSAvoidmanufacturing process

Core Design Contradiction:

Object-affected harmful factorsVSDevice complexity

Solution Approach 1:

The through holes are sealed with solder paste before the underfiller pouring process. This preliminary sealing action prevents underfiller from flowing into the through holes during the subsequent underfiller pouring step, eliminating the need for separate back-surface sealing operations and simplifying the manufacturing process

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

Solder paste serves as an intermediary material that fills and seals the through holes. This intermediary substance prevents direct contact between the underfiller and the through holes, blocking the harmful outflow path while maintaining process simplicity

Inventive Principle:

Principle #24Intermediary (Mediator)

2Object-affected harmful factors

If through holes are sealed on the back surface, then underfiller outflow is prevented, but the inside of through holes remains hollow allowing underfiller intrusion

Engineering Contradiction:

Improveunderfiller outflowVSAvoidjunction reliability

Core Design Contradiction:

Object-affected harmful factorsVSReliability

Solution Approach 1:

The harmful hollow space inside the through holes is removed by filling them with solder paste. This extraction of the problematic void space eliminates the pathway for underfiller intrusion while maintaining the structural integrity and electrical functionality of the through holes

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The hollow through holes, which initially represent a potential harm pathway for underfiller intrusion, are converted into beneficial sealed cavities filled with solder paste. The same through hole structure that could allow underfiller leakage is transformed into a protective element that prevents such leakage

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

3Object-affected harmful factors

If through holes are relocated to avoid underfiller overflow, then underfiller spread is prevented, but electrical characteristics may be compromised

Engineering Contradiction:

Improveunderfiller spreadVSAvoidelectrical characteristic

Core Design Contradiction:

Object-affected harmful factorsVSReliability

Solution Approach 1:

The through holes are segmented and individually filled with solder paste. This segmentation allows each through hole to be independently sealed, preventing underfiller spread while maintaining the original positions and electrical connectivity functions of the through holes in the circuit board design

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 approach reduces the need for extra underfiller, enhances junction reliability, and allows for optimal placement of through holes based on electrical characteristics, simplifying the manufacturing process and preventing underfiller spread.

Implementation Method 1

coating surfaces of a plurality of electrode pads and surfaces of through holes on an one side of the printed wiring board with a bonding material

Methodology Applied

Scientific EffectBonding: Adhesive

Implementation Method 2

filling a space between the semiconductor package and the printed wiring board with a filler material

Methodology Applied

Scientific EffectMelting: Melting

Data Source

PatentUS8101870B2Method for manufacturing printed circuit board, printed circuit board, and electronic apparatus

Publication Date: 2012.01.24 KIOXIA CORP

AI summary

A method for manufacturing a printed circuit board. The method includes: preparing a printed wiring board, the printed wiring board comprising through holes and a plurality of electrode pads; coating surfaces of the plurality of electrode pads and surfaces of the through holes on an one side of the printed wiring board with a bonding material; mounting a semiconductor package on the printed wiring board such that a plurality of bumps on a surface of the semiconductor package corresponds to the plurality of electrode pads; bonding the bumps to the electrode pads by heating the printed wiring board on which the semiconductor package is mounted; and filling a space between the semiconductor package and the printed wiring board with a filler material.