Embedded Solder Preform for Voiding Control in Electronic Assemblies
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Solution Overview
Problem
Solder voiding becomes problematic in large pad and component termination areas, such as in Quad Flat No-leads packages, due to trapped gases that reduce physical bonding strength and electrical and thermal conductivity, leading to reduced reliability of electronic assemblies.
Innovation Solution
Embedding a solder preform into the solder paste with a geometry that creates a gap between components, allowing gases to escape during reflow soldering, with the preform having a melting temperature similar to or higher than the solder paste to maintain this gap.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If solder paste is used to bond components to pads, then mechanical bonding and electrical connections are achieved, but trapped gases create voids that reduce bonding strength and conductivity
Solution Approach 1:
A preform is placed on the pad before applying solder paste. The preform creates a gap between the component and pad that allows gases to escape during reflow soldering, preventing void formation. This preliminary structural arrangement solves the voiding problem before the harmful effect occurs.
Solution Approach 2:
The preform acts as an intermediary element between the solder paste and the component/pad assembly. It provides a pathway for gas escape and maintains proper spacing, mediating the interaction between molten solder and trapped gases to prevent void formation.
2Productivity
If the pad area and component termination area are increased, then more components can be mounted, but solder voiding increases due to trapped gases
Solution Approach 1:
The preform is pre-positioned on large pads before solder paste application. This preliminary action ensures that even with increased pad area that would normally trap more gases, the gas escape pathway is already established, allowing larger components to be mounted without proportionally increased voiding.
3Object-generated harmful factors
If a preform is embedded in solder paste to create a gap for gas escape, then solder voiding is reduced, but the process complexity increases
Solution Approach 1:
The preform is placed on the pad before solder paste is applied. This preliminary action integrates the preform into the existing stencil printing and reflow process without requiring additional process steps, minimizing the increase in process complexity while achieving void reduction.
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
Reduces solder voiding from approximately 45% to 10%, improving the reliability and consistency of solder joints by allowing gases to escape, thereby enhancing bonding strength and conductivity.
Implementation Method 1
the preform has a melting temperature similar to or higher than the solder paste to maintain this gap
Implementation Method 2
the solder powder in the paste is melted and forms a solid mass, bonding the components to their respective metallization pads
Data Source
AI summary
Methods are provided for controlling voiding caused by gasses in solder joints of electronic assemblies. In various embodiments, a preform can be embedded into the solder paste prior to the component placement. The solder preform can be configured with a geometry such that it creates a standoff, or gap, between the components to be mounted in the solder paste. The method includes receiving a printed circuit board comprising a plurality of contact pads; depositing a volume of solder paste onto each of the plurality of contact pads; depositing a solder preform into each volume of solder paste; placing electronic components onto the printed circuit board such that contacts of the electronic components are aligned with corresponding contact pads of the printed circuit board; and reflow soldering the electronic components to the printed circuit board.