Cu Core Ball Solder Joint Alpha Dose Reduction
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Solution Overview
Problem
Existing technologies fail to effectively reduce alpha dose in solder joints used for high-density electronic component mounting, leading to soft errors and thermal stress issues due to the presence of radioactive isotopes in solder alloys, particularly in Cu core balls and Pb-Sn solder alloys, which are difficult to manage with current plating methods.
Innovation Solution
A core ball with a high-purity metallic powder coated with a Sn-Bi based Pb-free solder alloy, where the alpha dose is reduced by using a plating method that vaporizes radioactive elements during the manufacturing process, and the solder plating film is formed using a Sn-Bi alloy with Bi content between 40-60% to lower the junction temperature and thermal stress.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If Cu core ball or Pb-Sn solder alloy is used to support semiconductor package weight, then mechanical strength is improved, but alpha dose increases causing soft errors
Solution Approach 1:
The invention changes the chemical composition parameters of the solder alloy by completely eliminating Pb and strictly limiting Bi content to 0.01 wt% or less. This parameter change maintains mechanical strength while reducing alpha dose to 0.0100 cph/cm2 or less, resolving the contradiction between strength and alpha radiation harm.
Solution Approach 2:
The invention extracts and removes the harmful radioactive elements (Pb and Bi) from the solder alloy composition. By taking out these elements that cause alpha radiation, the solder paste achieves both mechanical strength through Cu powder and low alpha dose, resolving the technical contradiction.
2Area of stationary object
If high-density mounting is implemented to meet compact requirements, then mounting area is reduced, but soft error probability increases due to alpha ray exposure
Solution Approach 1:
The invention extracts harmful radioactive elements from the solder material used in high-density mounting. By removing Pb and limiting Bi to 0.01 wt% or less, the solder paste enables compact high-density mounting while reducing alpha ray exposure and soft error probability.
Solution Approach 2:
The invention changes the compositional parameters of the solder paste by eliminating Pb and strictly controlling Bi content. This allows high-density mounting to be implemented with reduced alpha dose (0.0100 cph/cm2 or less), thereby reducing soft error probability while maintaining compact design.
3Ease of manufacture
If conventional plating methods are used to form solder coating, then manufacturing process is simple, but radioactive isotopes remain causing high alpha dose
Solution Approach 1:
The invention changes the compositional parameters of the solder paste by completely eliminating Pb and limiting Bi to 0.01 wt% or less. This parameter change is achieved through careful selection of raw materials (Cu powder, flux, organic vehicle) and maintains manufacturing simplicity while reducing alpha dose to 0.0100 cph/cm2 or less.
4Temperature
If Bi content is increased to lower melting temperature, then junction temperature is reduced, but alpha dose increases causing soft errors
Solution Approach 1:
The invention changes the compositional parameters by strictly limiting Bi content to 0.01 wt% or less while eliminating Pb. This maintains a higher melting temperature but achieves much lower alpha dose (0.0100 cph/cm2 or less), resolving the contradiction between temperature control and alpha radiation harm.
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
The solution significantly reduces alpha dose to below 0.0200 cph/cm2, minimizing soft errors and thermal stress, while maintaining high sphericity and electrical conductivity of the Cu core balls, thereby enhancing the reliability of high-density electronic component mounting.
Implementation Method 1
the solder plating film is a Sn—Bi based Pb-free solder alloy including Bi in an amount of 40-60 mass percent
Implementation Method 2
the alpha dose is reduced by using a plating method that vaporizes radioactive elements during the manufacturing process
Data Source
AI summary
A core ball wherein a junction melting temperature and a low alpha dose are set for suppressing a soft error generation and solving a mounting problem. A metallic powder as a core is a sphere. A pure degree of a Cu ball of the metallic powder is equal to or higher than 99.9% but equal to or less than 99.995%. A contained amount of one of Pb and Bi or a total contained amount of Pb and Bi is equal to or higher than 1 ppm. A sphericity of the Cu ball is at least 0.95. A solder plating film for coating the Cu ball comprises Sn—Bi based alloy. U contained in the solder plating film is equal to or less than 5 ppb and Th is equal to or less than 5 ppb. An alpha dose of the core ball is equal to or less than 0.0200 cph/cm2.