PBGA Stiffener Flatness Control for Column Alignment
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Solution Overview
Problem
Plastic ball grid arrays (PBGAs) experience high solder joint strain due to mismatched thermal expansion coefficients with printed wiring boards, leading to premature failure, as existing solutions like high melt solder columns have not been successfully implemented due to warpage issues during assembly.
Innovation Solution
A thin metal or ceramic stiffener is bonded to the top of the PBGA to maintain flatness, combined with the use of high melt solder columns instead of solder balls for improved strain relief and alignment during temperature cycling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If solder balls are replaced with high melt solder columns, then solder joint reliability is improved, but warpage during assembly process worsens alignment
Solution Approach 1:
A stiffener is bonded to the top of the PBGA substrate before the column attach process to pre-establish flatness maintenance capability. This preliminary action ensures the substrate maintains its flatness during subsequent high-temperature column attachment and assembly soldering processes, preventing misalignment of the solder columns.
2Stability of the object's composition
If a stiffener is bonded to the PBGA substrate, then flatness is maintained during temperature cycling, but device complexity increases
Solution Approach 1:
The stiffener is designed as a thin plate with specific material properties (high modulus of elasticity) to provide the necessary stiffness. By optimizing the thickness and material parameters, the stiffener maintains substrate flatness during temperature cycling while minimizing the increase in device complexity.
3Reliability
If high melt solder columns are used instead of solder balls, then strain relief is improved, but manufacturing difficulty increases due to warpage control
Solution Approach 1:
The stiffener is attached before the column attach process to pre-establish flatness maintenance capability. This preliminary action ensures the substrate maintains its flatness during subsequent high-temperature column attachment and assembly soldering processes, preventing misalignment of the solder columns.
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 solution significantly reduces warpage and enhances solder joint reliability, allowing PBGA components to function reliably in harsh environments by maintaining alignment and strain relief between components and printed wiring boards.
Implementation Method 1
The CTE of the PBGA maybe significantly different from that of the printed wiring board to which it is soldered. bonding an aluminum plate to the top of a PBGA can result in a significant reduction in warping during temperature cycling
Implementation Method 2
a stiffener is bonded to the top of the component
Data Source
AI summary
A method and product which provides a thin metal or ceramic plate to the top of a plastic grid array (PGA) as a stiffener to maintain its flatness over temperature during a column attach process, and the columns are used for attachment to circuit boards or other circuit devices. These may be constructed in this manner initially or may be retrofitted plastic ball grid arrays from which the solder balls are removed and, the stiffener is attached to the top, and the solder columns have been added to replace the solder balls. The stiffener is a bonded thin metal or ceramic plate attached to the top of the PGA to maintain its flatness over temperature during the column attach process. An aluminum plate bonded to the top of a PGA results in a significant reduction in warping during a temperature cycle. This allows attachment of solder columns to the PBGA. The high melt solder columns are attached to an area array pattern on the PBGA substrate. This array is typically either a solid or perimeter grid. It is critical that the ends of the solder columns opposite the ends attached to the substrate align precisely with the matching grid of solder pads on the printed wiring board. The purpose of the stiffening plate is to maintain the flatness of the PBGA during the process of attaching the columns to the substrate as well as attaching the component to the printed wiring board such that the columns maintain their alignment over this temperature range.