Locking Dual Leadframe for Flip Chip Warpage Control
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Solution Overview
Problem
Flip chip on leadframe packages face issues with solder ball detachment due to lack of leadframe co-planarity, primarily caused by warpage during heated reflow processes and handling, leading to electrical opens and yield loss.
Innovation Solution
A locking dual leadframe (LDLF) design featuring a top metal frame portion with protruding features that penetrate apertures on a bottom metal frame portion, ensuring alignment and stability during assembly, thereby minimizing warpage and maintaining co-planarity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If solder ball size is increased to prevent detachment, then solder ball attachment reliability is improved, but solder ball collapse and solder smearing incidence increases causing yield loss
Solution Approach 1:
The patent changes the geometric parameters of the leadframe structure by adding protruding features that extend beyond the frame plane. This structural parameter change provides mechanical support to maintain co-planarity during assembly, allowing the use of smaller solder balls without detachment issues, thus resolving the contradiction between reliability and productivity
2Ease of manufacture
If conventional leadframe design is used, then manufacturing simplicity is maintained, but leadframe co-planarity is lost during assembly causing solder ball detachment
Solution Approach 1:
The leadframe is segmented into multiple components including a frame and separate protruding features that can be formed through die-stamping. This segmentation allows the protruding features to be created using conventional manufacturing processes while providing the necessary structural support for maintaining co-planarity and preventing solder ball detachment
3Device complexity
If leadframe warpage is not controlled, then assembly process simplicity is maintained, but leadframe co-planarity is lost leading to electrical opens
Solution Approach 1:
The protruding features are formed in advance during the die-stamping process, before assembly. These pre-formed features provide inherent mechanical support that maintains co-planarity throughout the assembly process, eliminating the need for additional warpage control measures and maintaining assembly simplicity while ensuring manufacturing precision
Data Source
AI summary
A method of assembling a flip chip on a leadframe package. A locking dual leadframe (LDLF) includes a top metal frame portion including protruding features and a die pad and a bottom metal frame portion having apertures positioned lateral to the die pad. The protruding features and apertures are similarly sized and alignable. A flipped integrated circuit (IC) die having a bottomside and a topside including circuitry connected to bond pads having solder balls on the bond pads is mounted with its topside onto the top metal frame portion. The top metal frame portion is aligned to the bottom metal frame portion so that the protruding features are aligned to the apertures. The bottomside of the IC die is pressed with respect to a top surface of the bottom frame portion, wherein the protruding features penetrate into the apertures.