Variable Ball Height BGA Packages via Solder Paste Transfer
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Solution Overview
Problem
Ball grid array (BGA) packages face challenges such as package warpage and the need to avoid flux or solder paste application near land-side components, which limits the minimum spacing between BGA balls and these components, especially as package form factors shrink, and existing standard ball pick-and-place technologies are costly and inefficient for varying ball heights.
Innovation Solution
A solder paste molding process using a template or mold with cavities of varying depths and diameters to accommodate spatial variations in the package, allowing for different ball heights and eliminating the need for direct flux or paste printing on the package, thereby reducing tooling costs and lead time, and enabling the use of a standardized solder paste transfer process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If standard ball pick-and-place technology is used to vary ball heights, then package warpage can be compensated, but manufacturing cost increases significantly
Solution Approach 1:
The patent changes the parameter of ball height by using solder paste transfer with varying paste volumes instead of physical ball size changes. This allows compensation for package warpage while using a single-pass process with standard equipment, avoiding the high costs associated with multi-pass pick-and-place operations.
Solution Approach 2:
The patent creates a copy of the ball structure using solder paste transfer rather than moving actual balls. The solder paste is transferred from a mold cavity to form balls on the substrate, allowing variable heights to be achieved through mold cavity depth variations rather than complex ball handling operations.
2Manufacturing precision
If multi-pass process is used to place different ball sizes, then variable ball heights can be achieved, but yield decreases due to ball displacement
Solution Approach 1:
The patent performs preliminary action by pre-forming solder paste balls in mold cavities with varying depths before transfer. This allows different ball heights to be prepared in advance and transferred in a single pass, eliminating the risk of ball displacement that occurs during multi-pass operations.
Solution Approach 2:
The patent merges multiple operations into a single step by combining variable ball height formation with a single solder paste transfer operation. Instead of separate operations for different ball sizes, the mold cavities are designed with varying depths to produce all required ball heights in one transfer cycle.
3Ease of operation
If flux or solder paste is applied near land-side components, then ball placement can be facilitated, but spacing requirements increase
Solution Approach 1:
The patent extracts the flux or solder paste application step from the ball placement process. By using a solder paste transfer process that does not require flux application near land-side components, the minimum spacing requirements are reduced, allowing more compact package designs.
Solution Approach 2:
The patent uses a mold as an intermediary to transfer solder paste directly to ball locations without requiring flux application in the vicinity of land-side components. This intermediary approach allows precise paste placement without the spacing constraints imposed by traditional flux-based methods.
Data Source
AI summary
BGA packages with a spatially varied ball height, molds and techniques to form such packages. A template or mold with cavities may be pre-fabricated to hold solder paste material applied to the mold, for example with a solder paste printing process. The depth and/or diameter of the cavities may be predetermined as a function of spatial position within the mold working surface area. Mold cavity dimensions may be specified corresponding to package position to account for one or more pre-existing or expected spatial variations in the package, such as a package-level warpage measurement. Any number of different ball heights may be provided. The molds may be employed in a standardize process that need not be modified with each change in the mold.