Compression-Loaded PCB Assembly for BGA Solder Defect Mitigation
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Solution Overview
Problem
Solder joint defects and separations occur during secondary reflow or rework processes due to mismatched thermal expansion coefficients and thermal gradients between VIPPO, deep-backdrilled VIPPO, and non-VIPPO structures on printed circuit boards, leading to tensile loads that can cause solder joints to disconnect.
Innovation Solution
A compression-loading assembly is applied to ASIC packages, using a top plate, compression plate, and adjustable compression mechanisms with springs to apply a uniform compression load that counteracts tension forces, preventing solder joint separation and maintaining joint integrity during reflow or rework.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If reflow soldering is performed on double-sided PCBs with components on both sides, then components can be attached to both sides of the PCB, but solder joint defects and separations occur due to mismatched thermal expansion coefficients and thermal gradients
Solution Approach 1:
The compression loading assembly applies a preliminary compressive force to the PCB assembly before and during the reflow soldering process. This pre-applied compression counteracts the tensile stresses that develop during heating due to thermal expansion mismatches between different PCB structures (VIPPO, deep-backdrilled VIPPO, and non-VIPPO), preventing solder joint separation and defects.
Solution Approach 2:
The system dynamically adjusts the compression load parameters during the reflow process. The compression force is modified in response to changing thermal conditions, maintaining optimal pressure on the solder joints throughout the heating and cooling cycles to prevent defects while accommodating thermal expansion variations.
2Reliability
If compression load is applied to counteract tensile forces during reflow, then solder joint separation is prevented, but the assembly requires additional compression mechanisms and springs
Solution Approach 1:
The compression loading assembly is divided into multiple independent compression mechanisms, each with its own spring element. These segmented units are distributed across the PCB assembly, allowing the compressive force to be applied at multiple locations simultaneously. This segmentation makes the complex system more manageable and enables uniform pressure distribution across the entire assembly.
Solution Approach 2:
The compression mechanisms serve multiple functions: they apply compressive force during reflow soldering, maintain pressure during cooling, and provide structural support for the PCB assembly. The same mechanical components are utilized throughout the manufacturing process, reducing the need for additional specialized equipment.
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 compression load effectively prevents solder joint separation and maintains joint integrity during secondary reflow or rework, ensuring reliable connections across different thermal expansion structures without deforming the solder joints or altering their stand-off distance.
Implementation Method 1
Each compression mechanism may include a compression member and at least one spring positioned on each compression member. The at least one spring may be located between the compression plate and the top plate.
Implementation Method 2
Solder joint defects and separations occur during secondary reflow or rework processes due to mismatched thermal expansion coefficients and thermal gradients between VIPPO, deep-backdrilled VIPPO, and non-VIPPO structures on printed circuit boards
Data Source
AI summary
The present disclosure provides systems for applying a compression load on at least part of an application specific integrated circuit (“ASIC”) ball grid array (“BGA”) package during the rework or secondary reflow process. The compression-loading assembly may include a top plate and a compression plate. The compression plate may exert a compression load on at least part of the ASIC using one or more compression mechanisms. The compression mechanisms may each include a bolt and a spring. The bolt may releasably couple the top plate to the compression plate and allow for adjustments to the compression load. The spring may be positioned on the bolt between the top plate and the compression plate and, therefore, may exert a force in a direction away from the top plate and toward the compression plate. The compression load may retain the solder joint and may prevent the solder separation defect during the reflow process.