Actively Cooled Heatshield for Clamshell BGA Rework
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Solution Overview
Problem
During the rework of a second BGA package in a clamshell BGA structure, the first BGA package on the opposite side of the PCB is prone to solder joint defects due to excessive heat, leading to hot tears, separation, and joint failure.
Innovation Solution
A heatshield with active cooling capability is applied to the first BGA package, utilizing a backer plate, a metal plate, and package pedestal to direct cooling gas towards the metal plate and the first BGA package, maintaining the solder joint temperature below the reflow and solidus temperatures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If active cooling is applied to the first BGA package during rework of the second BGA package, then solder joint defects are prevented and reliability is improved, but device complexity increases due to the heatshield structure with air inlet ports, ducting, and vents
Solution Approach 1:
A heatshield structure is introduced as an intermediary component between the rework area (second BGA package) and the protected area (first BGA package). The heatshield includes a backer plate with air inlet ports, air inlet ducting, and vents that direct cooling gas flow. This intermediary structure actively manages thermal energy distribution to prevent solder joint defects while maintaining a relatively simple overall design
Solution Approach 2:
The heatshield utilizes pneumatic principles by incorporating air inlet ports connected to a cooling gas source, air inlet ducting to channel the gas, and vents to direct the cooling flow toward the first BGA package. This pneumatic system actively removes thermal energy from the protected BGA package during rework operations, preventing solder joint defects without requiring complex active cooling mechanisms
2Reliability
If cooling gas is directed towards the first BGA package to maintain temperature below reflow and solidus temperatures, then solder joint defects are prevented, but the rework process complexity increases
Solution Approach 1:
The heatshield applies local quality by directing cooling gas flow specifically to the first BGA package area that requires temperature control during rework. The backer plate includes strategically positioned air inlet ports, air inlet ducting, and vents that channel cooling gas precisely where needed. This localized cooling approach maintains solder joint temperatures below reflow and solidus temperatures without requiring system-wide complex cooling infrastructure
Solution Approach 2:
The system controls the temperature parameter of the first BGA package by adjusting the cooling gas flow through the heatshield. By modifying the flow rate and distribution of cooling gas through the air inlet ports and vents, the system maintains the solder joint temperature within the safe range (below reflow and solidus temperatures) during the rework process, preventing defects without requiring overly complex temperature control mechanisms
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 active cooling of the heatshield effectively prevents solder joint defects in the first BGA package during the rework of the second BGA package, maintaining the solder joints in a solid state and preventing reflow-related issues.
Implementation Method 1
cooling gas may be forced into the heatshield via the air inlet port and/or air inlet ducting. The cooling gas is directed towards the metal plate and the first BGA package
Implementation Method 2
The heatshield may absorb thermal energy, or heat, during rework of the second BGA package
Implementation Method 3
The cooling gas is directed towards the metal plate and the first BGA package... The heatshield may absorb thermal energy, or heat, during rework of the second BGA package
Data Source
Figure 1
Figure 2A
Figure 2B
AI summary
The present disclosure provides for a heatshield that can be actively cooled during a rework process. The heatshield may include a backer plate, a metal plate, and/or a package pedestal. The backer plate may include one or more air inlet ports configured to be connected to an air compressor. Air inlet ducts may extend from the air inlet ports through at least a portion of the backer plate. A plurality of vents may extend from the air inlet ducts to a top surface of the backer plate such that the plurality of vents directs cooling gas forced into the heatshield towards the metal plate and a first BGA. The cooling gas may maintain the solder joint temperature of the first BGA package below the reflow temperature and below the solidus temperature of the solder joints to prevent reflow-related solder joint defects from occurring in the first BGA package during rework of a second BGA package.