Cooling Heatshield Venting for Clamshell BGA Solder Joint Protection
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Solution Overview
Problem
During the rework of ball grid array (BGA) packages on printed circuit boards, solder joint defects can occur due to temperature variations, leading to issues like hot tears, separation, and joint failure, especially in clamshell BGA configurations with Via-in-Pad-Plated-Over (VIPPO) and non-VIPPO designs, where increased temperature variations during the reflow process can cause warpage-related defects.
Innovation Solution
A heatshield with active cooling capability is applied to the bottom-side BGA package during the rework of the top-side BGA package, using a backer plate and a finned metal plate with air inlet ports and ducting to direct cooling gas towards the metal plate, maintaining the solder joint temperature below the reflow and solidus temperatures, thus preventing solder joint defects.
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, but device complexity increases
Solution Approach 1:
A heatshield comprising a backer plate and a metal plate is introduced as an intermediary component between the rework area and the first BGA package. The heatshield absorbs excess thermal energy and directs cooling gas to prevent heat transfer to the solder joints, thereby protecting them without requiring modification to the BGA packages themselves
Solution Approach 2:
A pneumatic cooling system is implemented using an air compressor connected to the heatshield through air inlet ports and ducting. Cooling gas is forced through the heatshield structure to actively remove heat from the first BGA package area, maintaining solder joint temperatures below critical thresholds during the rework process
2Temperature
If cooling gas is directed towards the solder joint area, then the first BGA package is cooled, but rework cannot occur on the second BGA package
Solution Approach 1:
The heatshield is designed with differentiated zones: a first surface facing the second BGA package allows heat absorption and rework operations, while internal ducting and a second surface direct cooling gas specifically to the first BGA package area. This localized cooling approach cools only the necessary region without interfering with the rework process on the opposite side
3Reliability
If the metal plate absorbs thermal energy, then the first BGA package is protected from heat, but the heatshield structure becomes more complex
Solution Approach 1:
The heatshield employs a composite structure consisting of a backer plate and a metal plate with high thermal conductivity. The metal plate serves as the primary thermal absorption component, while the backer plate provides structural support and houses the cooling ducting. This composite design efficiently manages heat transfer while maintaining structural integrity
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 system effectively prevents solder joint defects by maintaining the temperature of the first BGA package below the reflow temperature, ensuring the solder joints remain solid and preventing hot tears, separation, and joint failure during the rework of the second BGA package.
Implementation Method 1
The cooling gas may be configured to decrease a temperature of at least one of the metal plate and the backer plate
Implementation Method 2
The heatshield may absorb thermal energy, or heat, during rework of the second BGA package
Data Source
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.