Varied BGA Solder Ball Architecture for SMT Warpage Defects
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Solution Overview
Problem
The dynamic warpage of flip chip ball-grid-array (BGA) packages leads to various defects during surface mount technology (SMT) processes, such as solder bump bridging, head on pillow, non-contact open, and non-wet open, due to compression and shape variations, which existing solutions like stiffeners, stencil design optimization, and land side components fail to adequately address.
Innovation Solution
The use of first solder balls for majority interconnects and strategically placed second solder balls with different volumes and compositions, including cored solder balls with a non-melting core, to act as collapse limiters and stand-offs, reducing defects and accommodating warpage without occupying additional real estate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If stiffeners are added to the package substrate to address warpage, then warpage control is improved, but the available real estate on the top side of the package is reduced
Solution Approach 1:
The patent moves the warpage compensation function from the top side (2D plane) to the vertical dimension by using stand-off structures on the bottom side of the package substrate. This dimensional shift allows stiffeners to be placed on the backside, freeing up top-side real estate while maintaining warpage control through vertical stand-off geometry.
Solution Approach 2:
The patent uses land side components (LSCs) that replicate the stand-off function of traditional top-side stiffeners but are positioned on the bottom side of the substrate. These copied structures provide equivalent mechanical support and warpage compensation without occupying premium top-side real estate.
2Reliability
If land side components are used as stand-off during SMT to prevent solder ball bridging, then SBB prevention is improved, but the choice of height is limited and height variations are large
Solution Approach 1:
The patent employs cored solder balls with precisely controlled core diameters that directly determine stand-off height. By varying the core diameter parameter, the design achieves precise height control (within ±10 microns) that is not achievable with conventional LSCs. The core acts as a mechanical stop that limits solder ball compression to a predetermined height.
Solution Approach 2:
The patent uses composite cored solder balls consisting of a non-solder core material surrounded by a solder material layer. This composite structure provides both the stand-off function (through the non-melting core) and the soldering function (through the outer solder layer), while the core diameter precisely controls the stand-off height.
3Reliability
If stencil design optimization is used to tailor paste volumes to control solder volumes, then SBB prevention is improved, but the printing process limits are approached and further paste volume reduction is difficult
Solution Approach 1:
The patent introduces cored solder balls as an intermediary element that provides mechanical stand-off and compression limitation during the SMT process. This intermediary structure prevents solder ball bridging through physical geometry rather than relying solely on optimized paste volumes, thereby avoiding the need to push printing processes beyond their capabilities.
4Reliability
If copper bumps or pillars are used on the motherboard to serve as stand-off during SMT, then SBB prevention is improved, but SMT process changes are required and package and mother board real estate is occupied
Solution Approach 1:
The patent merges the stand-off function and the interconnect function into a single cored solder ball component. The cored solder ball simultaneously provides mechanical stand-off during assembly and electrical interconnect after reflow, eliminating the need for separate copper bumps or pillars on the motherboard and avoiding additional SMT process steps.
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 approach improves yield and tolerance to assembly and handling variations, reduces the need for stencil revisions, and eliminates or relaxes the need for stiffeners, effectively minimizing SMT defects and enhancing assembly processes.
Implementation Method 1
second solder balls with different volumes and compositions, including cored solder balls with a non-melting core
Data Source
AI summary
Embodiments disclosed herein include electronic packages. In an embodiment, the electronic package comprises a first substrate; a second substrate; and an array of interconnects electrically coupling the first substrate to the second substrate. In an embodiment, the array of interconnects comprises first interconnects, wherein the first interconnects have a first volume and a first material composition, and second interconnects, wherein the second interconnects have a second volume and a second material composition, and wherein the first volume is different than the second volume and/or the first material composition is different than the second material composition.