LGA Package Land Solder Joint Control for Bridging Prevention
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Solution Overview
Problem
The challenge in the field of printed circuit boards is the occurrence of solder bridging and open solder joint failures due to the warpage and undulation of ceramic substrates during the bonding process, which affects the flatness and alignment of lands on LGA semiconductor packages, leading to issues with solder distribution and flux separation.
Innovation Solution
The solution involves forming a printed circuit board where the semiconductor package and printed wiring board are bonded with solder, with specific land arrangements and solder bonding areas that ensure the solder height is 30% or less of the land diameter, and a ratio of solder bonded area on the printed wiring board to the package substrate land is between 56% and 81%, to manage surface tension and flux distribution effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If ceramic material is used for package substrate to reduce dust emission and improve heat dissipation, then reliability and thermal management are improved, but warpage and undulation occur during baking, deteriorating manufacturing precision and land flatness
Solution Approach 1:
The patent applies parameter changes by carefully controlling the baking temperature profile and duration to minimize thermal stress and warpage in ceramic substrates. By optimizing the heating parameters during the baking process, the patent reduces undulation while maintaining the dust-resistant and heat-dissipating properties of ceramic materials.
2Device complexity
If LGA semiconductor package is used to reduce height and simplify manufacturing, then device complexity and height are reduced, but solder bridging and open solder joint failures occur due to substrate warpage, deteriorating reliability
Solution Approach 1:
The patent applies local quality by creating a convex portion on the package substrate specifically at the land area. This localized structural modification ensures that the land surface remains flat and properly aligned with the printed wiring board, while other areas of the substrate can accommodate the overall warpage without affecting solder joint integrity.
Solution Approach 2:
The patent applies preliminary action by pre-forming the convex portion on the package substrate before the soldering process. This advance preparation compensates for the warpage that will occur during baking, ensuring that the land surface is properly positioned relative to the printed wiring board before soldering begins, thereby preventing solder bridging and open joint failures.
3Productivity
If lands are arranged at finer pitch to achieve high pin count with smaller package, then productivity and integration density are improved, but solder distribution control becomes more difficult, deteriorating manufacturing precision
Solution Approach 1:
The patent applies local quality by providing each land with a dedicated convex portion that ensures proper solder distribution. This localized structural feature maintains consistent solder height and prevents bridging between adjacent lands, even when lands are arranged at fine pitch, thereby enabling high pin count while maintaining manufacturing precision.
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 configuration reduces the risk of solder bridging failure by controlling the force of surface tension and facilitates the proper spreading of solder, thereby minimizing open solder joint failures and ensuring reliable bonding despite substrate undulations.
Implementation Method 1
a land of a semiconductor package and a land of a printed wiring board are bonded to each other by solder
Implementation Method 2
The extended molten solder produces force of reducing a surface area due to the surface tension. That is, force of reducing the distance between the package substrate and the printed wiring board occurs.
Data Source
AI summary
A plurality of lands is formed apart from each other on a surface of a package substrate. Another plurality of lands is formed apart from each other on a surface of a printed wiring board. The surface of the package substrate and the surface of the printed wiring board face each other. The plurality of lands and another plurality of lands are bonded to each other with solder having a height of 30% or less of a diameter of a solder bonding portion at the corresponding land. A ratio of a solder bonded area of at least each of lands, among another plurality of the lands, of which distance value to a corresponding one of the lands is larger than an average distance value between the lands and another lands, to a solder bonded area of the corresponding one of the lands is 56% or more and 81% or less.