Background

In the realm of semiconductor technology, the invalidation of patents is particularly challenging. One such litigation case we encountered involved claims embedded in complex trigonometric calculations protected by specific numerical restrictions. Our client—a semiconductor manufacturer—was trying to validate the novelty of the printed wiring board manufacturing method covered with a solder resist layer with at least one solder bump opening exposed to the connection pad. The client was expecting the depth of solar resist opening “D” to be between 3 μm and 18 μm, based on the following equation:

Wherein “R” is the radius of the solder ball, and “W” is the diameter of at least one opening in the solder resist layer

Client Challenge

Our client was facing challenges while analyzing this claim due to:

● Keyword Restrictions: Traditional keyword searches yielded limited relevant references.

● F-term Limitations: Functional terms (F-terms) related to the claim were scarce, making it difficult to pinpoint exact prior art.

Our Actionable Strategy

To address these challenges, we undertook a systematic approach, including:

● Figure Analysis: We examined the figures in the patent to understand the geometric relationships represented by the formula.

● Derivation and Numerical Analysis: We derived multiple forms of the formula and calculated their numerical values to ensure they fell within the range of the protected claim. This helped identify potential prior art that matched the mathematical relationships.

● Objective Analysis: During the approval stage of the project, we discussed the main agenda of the invention with the client. Based on that, we encountered our second-best prior art with no equation involved.

Impact

Our thorough analysis led us to identify two Tier 1 prior art references that were crucial in challenging the validity of the claim. These references demonstrated similar mathematical derivations and numerical values, thus providing strong evidence for invalidation.

One of the references summarizes the arrangement of high-temperature solder balls and recessed openings to eliminate sticking and prevent excessive clinging. If the high-temperature solder ball diameter is B [considered as the diameter of the solder ball (2R), the recess opening diameter is X (considered as diameter of the opening in the solder resist layer(W))] and the recess depth is t (considered as depth D, from the solder resist layer to the exposed connection pad), then [B−√(B^2-X^2)>2t] to avoid cracking of the low-temperature solder in the solder electrode, where B ≥ 1.2X.

The reference discloses a similar equation but different terminologies, further deriving the equation and value of depth from the given equation:

Here, B is the diameter of the solder ball (so, B=2R), W=X, and t=D; so, deriving the formula in terms of R and X, we have 2t < B −√(B^2-X^2)

2D < 2R−√((2R)^2-W^2)); dividing by 2

D ≤ R−√[R^2−(W/2​)^2]​ (proved)

Now, solving the equation for depth “t,” putting the values in the equation: 2t < B −√(B^2-X^2)

Given: B ≥ 1.2X, 2t < B −√(B^2-X^2) and B ≥ 108

t < B/2 – √[(B/2)^2 – (X/2)^2]

t < 108/2 – √[(108/2)^2-(90/2)^2]

t < 24 μm (approx.)

The depth (t) derived from the internal calculations falls below 24 μm, which was the main requirement of the subject patent claim.

The second reference discloses the height of the solder drop within the tape opening is calculated, and a tape thickness ratio (T1/T2) is derived. The ratio between the tape thickness (T1) and the tape opening diameter (T2) is equal to or greater than 1. This implies that a tape thickness ratio (T1/T2) of 1 indicates that there will be no gap between the solder bump and electrode pattern, which was the objective of the subject patent; here, the equation and other dimensions were not given, but the aim of the invention is fulfilled.