Injection Molded Solder Bumps on Fine Pitch Substrates
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Solution Overview
Problem
Current solder bump formation technologies face challenges in fine pitch applications under 150 microns, particularly with solder volume reduction and increased costs for preformed solder balls, as well as difficulties in forming solder bumps on C4 and capacitor pads in a single step process.
Innovation Solution
The method involves using a flexible unitary mask with through holes to directly inject molten solder into recessed regions of a substrate, allowing it to solidify, and then peeling the mask off, which allows for the formation of solder bumps on fine pitch substrates with reduced alignment steps and improved transfer yield, using a compliant material to ensure good contact and prevent solder leakage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the stencil printing method is used to form solder bumps on organic substrates, then the manufacturing cost is reduced, but the solder volume reduction after reflow prevents extension to fine pitch applications under 150 microns
Solution Approach 1:
The patent changes the physical state parameter of solder from solid paste to molten liquid, enabling direct injection into fine pitch pads without reflow volume reduction. This parameter change allows achieving both low cost (avoiding lithography/vacuum equipment) and fine pitch capability (under 150 microns) simultaneously
Solution Approach 2:
The patent replaces the mechanical stencil printing system with an injection molding system that uses gas pressure to force molten solder through a mask directly onto pads. This substitution eliminates the need for complex lithography or vacuum processing while maintaining fine pitch accuracy
2Quantity of substance
If preformed solder balls are used to eliminate volume reduction, then the solder volume is maintained, but the cost significantly increases with size reduction for finer pitch applications
Solution Approach 1:
The patent uses a disposable single-layer mask instead of expensive preformed solder balls. The mask is a low-cost flexible substrate with open circles that can be discarded after one use, eliminating the high cost associated with manufacturing and handling precision preformed solder balls for fine pitch applications
3Manufacturing precision
If the ball mounting method is used to form solder bumps on C4 pads, then the solder bumps are formed, but additional stencil printing is required for capacitor pads needing 20 times the solder volume
Solution Approach 1:
The patent creates a universal injection molding process that can handle both C4 pads and capacitor pads in a single step. By using a single mask layer with appropriately positioned openings and controlling injection parameters, the system performs multiple functions (forming different solder volumes on different pad types) without requiring additional 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 enables the formation of solder bumps on fine pitch substrates under 150 microns with reduced alignment steps and improved yield, using a single layer decal and compliant materials to ensure good contact and prevent solder leakage, thus addressing the limitations of existing technologies.
Implementation Method 1
The molten solder is forced under gas pressure into the cavity in the injection plate disposed above the array of cavities in the mold
Implementation Method 2
The molten solder is forced into the array of cavities in the mold. The injection plate is advanced to slide over the mold to wipe away the excess solder above the mold
Implementation Method 3
The injection plate is advanced to slide over the mold to wipe away the excess solder above the mold at a plurality of wiping apertures in the injection plate
Implementation Method 4
a substrate having a plurality of wettable pads in recessed regions defining volumes; aligning the through holes with the wettable pads; directly injecting molten solder through the through holes of the flexible unitary mask into the volumes with the wettable pads
Data Source
AI summary
A flexible unitary mask has a plurality of through holes. A substrate has a plurality of wettable pads in recessed regions defining volumes. The through holes are aligned with the wettable pads. Molten solder is directly injected through the through holes of the flexible unitary mask into the volumes with the wettable pads, such that the through holes and the volumes with the wettable pads are filled with solder. The solder is allowed to solidify, forming a plurality of solder structures adhered to the wettable pads. The flexible unitary mask is peeled from the substrate after the solder has solidified.