BGA Underfill Reservoir Assembly for Reflow Soldering
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Solution Overview
Problem
Traditional underfilling methods for ball grid arrays (BGAs) are time-consuming and challenging, especially in densely packed PCB layouts, often requiring needle injection which reduces available space for traces.
Innovation Solution
A BGA assembly with underfill channels in the component substrate and a reservoir cavity filled with underfill material and gas, where the gas pushes the underfill material through channels during reflow, allowing for automatic underfilling without additional steps or manual methods.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If traditional needle injection method is used for underfilling, then underfill material can be injected into tight spaces, but the process becomes time-consuming and reduces available space for PCB traces
Solution Approach 1:
The underfill material is pre-loaded into a reservoir cavity within the BGA package before assembly, eliminating the need for post-assembly injection. This preliminary preparation allows the underfill to be automatically dispensed during reflow soldering through pre-formed channels in the PCB, significantly reducing process time while maintaining precision in tight spaces
Solution Approach 2:
The BGA package is designed with self-contained underfill delivery capability through integrated reservoir cavities and flow channels. During reflow soldering, the heat automatically melts the underfill material which then flows through the channels to the joint interfaces without requiring external injection equipment or manual intervention, making the system self-sufficient
2Ease of manufacture
If needle filling opening is fabricated in PCB, then underfill can be injected from back side, but available space for running traces in multilayered PCB is reduced
Solution Approach 1:
The underfill reservoir cavity is nested within the BGA package structure itself, utilizing the existing package volume. This nesting approach eliminates the need for separate PCB openings while maintaining accessibility for underfill delivery, as the material is contained within the package and delivered through integrated channels rather than requiring external PCB access points
Solution Approach 2:
The underfill delivery system transitions from a two-dimensional PCB surface approach to a three-dimensional volume-based approach. By storing underfill material within the vertical volume of the BGA package and delivering it through vertical channels, the system eliminates the need for horizontal PCB trace routing space while maintaining effective underfill delivery
3Reliability
If multi-step traditional underfilling method is used, then underfill can be provided, but the process becomes complex and time-consuming
Solution Approach 1:
The underfill delivery system merges multiple functions into a single integrated structure: the reservoir cavity stores the underfill material, the pre-formed channels provide the delivery pathway, and the package structure itself serves as the containment and delivery mechanism. This consolidation eliminates the need for separate injection equipment, multiple processing steps, and external tooling, reducing process complexity while ensuring reliable underfill application
Solution Approach 2:
The BGA package structure is designed to serve multiple functions: it provides mechanical support for the component, contains the underfill reservoir, provides the delivery channels, and facilitates the underfill dispensing during reflow. This multi-functionality eliminates the need for dedicated underfilling equipment and processes, simplifying the overall manufacturing workflow while maintaining connection reliability
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
This method provides efficient and space-saving underfilling, sealing the channels upon cooling, enhancing the strength between the component substrate and PCB, and reducing the need for secondary underfill steps.
Implementation Method 1
A ball grid array (BGA) assembly includes a gas disposed in the reservoir cavity above the underfill material to push the underfill material through the underfill channels when the underfill material is in a liquid state
Implementation Method 2
The underfill material in the cavity can be in an uncured state (in either in a solid or liquid state) at an operating temperature below reflow temperature and in liquid state at least at or above reflow temperature
Data Source
Figure 1~2A
Figure 2B~2C
Figure 3A~3B
AI summary
A ball grid array (BGA) assembly (100) can include a component substrate (101) having at least one underfill channel (107) defined therethrough providing fluidic communication between a first side (103) of the component substrate (101) and a second side (105) of the component substrate (101), a plurality of pads or leads exposed on the second side (105) and configured to be soldered to a mating PCB, a cover (115) mounted to the component substrate (101) defining a reservoir cavity (117) between the first side (103) and the cover (115), and an underfill material (119) disposed within the reservoir cavity (117) such that the underfill material (119) can flow through the at least one underfill channel (107) to a gap defined between the second side and the mating PCB when the component substrate (101) is being soldered to the mating PCB.