Solder Interconnect Reflow Normalization After Test Board Removal
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Solution Overview
Problem
The removal of circuit package modules from test boards results in uneven solder ball heights, making it difficult to remount the modules to different test boards or clamp them to test fixtures.
Innovation Solution
A system and method involving a fixture with a recess and a stencil having apertures that align with solder interconnects, applying solder paste through these apertures, and heating to reflow the interconnects, ensuring uniform height.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If circuit package modules are removed from test boards for subsequent testing, then the modules can be reused on different test boards, but the solder balls become uneven in height making remounting difficult
Solution Approach 1:
The patent applies preliminary action by performing the solder paste application and reflow process immediately after module removal from the test board. The stencil is positioned and solder paste is applied before the module is moved to the next test board, ensuring the solder balls are normalized in height prior to subsequent mounting operations. This preliminary normalization action prevents the development of height variations that would occur if the module were reused directly without treatment.
Solution Approach 2:
The patent utilizes parameter changes by controlling the reflow heating process to melt and reshape the solder balls. The heating process raises the temperature to the solder reflow point, causing the solder to become molten and then solidify into uniform spherical shapes. This thermal parameter change transforms the uneven solder ball heights into uniform heights, resolving the contradiction between reusability and height uniformity.
2Manufacturing precision
If solder paste is applied through a stencil with apertures, then solder paste is precisely deposited onto solder interconnects, but the process requires additional equipment and steps
Solution Approach 1:
The stencil serves multiple functions: it acts as a mask for precise solder paste application, provides structural support during the process, and ensures proper alignment between the solder paste deposits and the underlying solder interconnects. By combining these functions into a single component, the patent achieves precise deposition without proportionally increasing system complexity.
Solution Approach 2:
The stencil acts as an intermediary tool between the solder paste application system and the solder interconnects. It mediates the deposition process by controlling where the paste is applied through its aperture pattern, which matches the interconnect layout. This intermediary approach enables precise deposition while keeping the overall system relatively simple, as the stencil is a passive component that requires no active control mechanisms.
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 method effectively normalizes solder interconnect heights, improving planarity and facilitating remounting to test boards or fixtures, with significant reductions in height variation from 44 μm to less than 16 μm.
Implementation Method 1
heating the circuit package module to reflow the solder interconnects with the added solder paste
Implementation Method 2
heating the circuit package module to reflow the solder interconnects
Data Source
AI summary
A method for normalizing the solder interconnects (e.g., normalizing the height of the solder ball interconnects) in a circuit package module (e.g., dual-sided mold grid array package module) after removal from a test board includes receiving in a fixture the circuit package module upside down and removably coupling a stencil to the fixture and over the circuit package module. The stencil has a pattern of apertures that coincides with the pattern of solder interconnects of the circuit package module. The method also includes applying solder paste over the stencil to pass through the apertures to add solder paste to the solder interconnects. The method also includes removing the stencil from over the fixture, and removing the circuit package module from the fixture. The circuit package module can be heated to reflow the solder interconnects with the added solder paste.