LGA Discrete Pads for PCB Flatness Compensation
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Solution Overview
Problem
Land grid arrays on printed circuit boards face challenges in maintaining flatness due to variations in the board's profile caused by other components and features, which can lead to poor electrical contact with surface mount components.
Innovation Solution
A method involving the formation of a grid array with metal pads plated directly onto a printed circuit board, where discrete metal pads are soldered over each plated pad, with varying thicknesses selected to compensate for deviations in flatness, ensuring a planar surface for better contact.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If metal pads are plated directly onto a printed circuit board, then the manufacturing process is simplified and cost is reduced, but the flatness of the pad surface deteriorates due to board profile variations
Solution Approach 1:
A separate flat metal pad piece is introduced as an intermediary component between the PCB and the surface mount device. This discrete pad is soldered to the plated pad on the PCB, and its flat upper surface provides the necessary planarity for reliable electrical contact, effectively mediating between the non-flat PCB surface and the requirement for flat contact surfaces.
Solution Approach 2:
The pad structure is segmented into two separate components: a plated pad on the PCB and a discrete flat metal pad piece. This segmentation allows each component to perform its specific function optimally - the plated pad provides electrical connection to the board while the discrete pad provides a flat contact surface, resolving the contradiction between manufacturing simplicity and surface flatness.
2Manufacturing precision
If discrete pads of varying thicknesses are soldered onto plated pads, then the flatness of the contact surface is improved, but the device complexity and manufacturing steps increase
Solution Approach 1:
The solution applies local quality by providing flatness compensation only at specific locations where the PCB profile deviates from flatness. Each discrete pad's thickness is customized for its specific location in the grid array, allowing the structure to maintain simplicity overall while providing localized corrections where needed.
3Reliability
If fully encapsulated gold plating is used on pads, then electrical contact and corrosion resistance are improved, but manufacturing cost increases significantly
Solution Approach 1:
Instead of applying expensive encapsulated gold plating to the entire PCB pad structure, the invention uses a more cost-effective discrete metal pad piece with a flat surface. This discrete pad provides the necessary electrical contact quality and can be manufactured more economically, sacrificing the long-term durability of encapsulated plating for immediate cost savings and manufacturing simplicity.
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 solution provides a land grid array with greater flatness than the printed circuit board, enhancing electrical contact and reducing issues like via snagging, while offering a cost-effective alternative to fully encapsulated gold plating.
Implementation Method 1
a grid array of metal pads plated directly onto a printed circuit board
Implementation Method 2
a discrete metal pad soldered to each of the plated metal pads in the grid array
Data Source
AI summary
A land grid array (LGA) includes a grid array of metal pads plated directly onto a printed circuit board, and a discrete metal pad soldered to each of the plated metal pads in the grid array. Each discrete metal pad has an exposed contact surface after soldering, and a thickness of each discrete metal pad is selected as a function of location in the grid array so that the discrete pads provide a locus of exposed surfaces having greater flatness than the printed circuit board.