Controlled Solder Height Packages Warpage Compensation
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Solution Overview
Problem
The thermal expansion mismatch between a package substrate and a die structure during the formation of ball grid array (BGA) solder interconnections leads to substrate warpage, increasing the risk of solder bridging and open connections due to uneven solder distribution, which can result in electrical shorting or failure to connect between the substrate and a printed circuit board.
Innovation Solution
Varying the amount of solder at different locations on the substrate by using stencils with openings of different sizes to ensure that the center and outer solder regions have different volumes, compensating for warpage and ensuring proper contact during the reflow process, thereby minimizing the risk of bridging and open connections.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If uniform solder volume is used across all locations on the substrate, then the manufacturing process is simple, but substrate warpage causes solder bridging in the center and open connections at the outer portions
Solution Approach 1:
The patent applies local quality by varying the solder ball volume based on location on the substrate. The stencil has different opening sizes: larger openings at outer portions to provide more solder volume, and smaller openings at the center to provide less solder volume. This compensates for substrate warpage during reflow, ensuring proper solder joint formation at all locations without bridging or open connections.
2Reliability
If larger solder balls are used at outer portions and smaller solder balls are used at the center, then solder distribution compensates for warpage, but the manufacturing process becomes more complex
Solution Approach 1:
The patent uses a stencil as an intermediary tool to achieve variable solder ball volumes. The stencil contains openings of different sizes positioned at different locations on the substrate. During the solder ball placement process, the stencil is applied to the substrate, and solder paste is printed through the stencil openings. This intermediary approach allows precise control of solder volume at each location without requiring complex manual placement or multiple different solder ball sizes, thus achieving reliability while keeping the manufacturing process relatively simple.
3Manufacturing precision
If the substrate is heated to reflow temperature, then solder joints are formed, but thermal expansion mismatch causes substrate warpage that moves solder bumps away from the PCB at outer portions
Solution Approach 1:
The patent applies preliminary anti-action by pre-compensating for the substrate warpage that will occur during heating. The stencil is designed with larger openings at outer portions and smaller openings at the center, which is the opposite of the warpage deformation pattern. When the substrate is heated and warps convexly on the BGA surface, the pre-positioned solder balls with location-dependent volumes ensure that outer portion solder balls (which would be pushed away) have larger initial volumes to maintain contact, while center solder balls (which move closer) have smaller volumes to prevent bridging. This preliminary compensation counteracts the harmful effects of thermal expansion mismatch.
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 effectively reduces the risk of solder bridging and open connections by adjusting solder volumes based on location, ensuring reliable interconnects between the substrate and the PCB, even as the substrate warps and flattens with temperature changes.
Implementation Method 1
thermal expansion mismatch between a substrate and a die structure positioned thereon may cause the substrate to warp and bend
Implementation Method 2
heated, the substrate begins to flatten out with the increased temperature and at the reflow temperature the substrate converts to a convex shape
Data Source
AI summary
An apparatus comprises a substrate including a surface and a plurality of bonding pads positioned on the surface. The apparatus also includes a material comprising a solder positioned on the bonding pads and extending a distance outward therefrom. A first of the bonding pads in a first location on the substrate surface includes the solder extending a first distance outward therefrom. A second of the bonding pads in a second location on the substrate surface includes the solder extending a second distance outward therefrom. The first distance is different than the second distance. Other embodiments are described and claimed.