Apertured Substrate for Lead Frame Molding Flash Prevention
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Solution Overview
Problem
Conventional packaging methods for leaded microelectronic devices often result in mold flash over solder balls due to incomplete contact between mold projections and ball-pads, and the force of mold compound can cause lead frames to bend, leading to defective devices with impaired structural and electrical connections.
Innovation Solution
A substrate with apertures aligned with lead frame pads is used to prevent mold compound from covering the pads and to enhance the rigidity of the lead frame, ensuring complete contact with the printed circuit board during attachment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional packaging methods are used with mold projections to contact ball-pads, then the molding process can be completed, but mold flash forms over solder balls due to incomplete contact
Solution Approach 1:
A substrate is introduced as an intermediary component between the lead frame and the mold compound. The substrate includes a surface with openings that expose lead frame pads, allowing the mold compound to flow through the openings and make direct contact with the pads without forming flash over the solder balls. This mediator structure resolves the contact issue while preventing flash formation.
2Productivity
If mold compound flows into the mold cavity with sufficient force to ensure filling, then complete molding is achieved, but the flexible lead frame bows or bends under the pressure
Solution Approach 1:
The substrate provides localized structural support at critical areas where the lead frame is susceptible to deformation. By positioning the rigid substrate beneath the lead frame in the mold cavity, the local quality of the assembly is enhanced at these vulnerable points, allowing the mold compound to flow with sufficient force to complete filling without causing lead frame bowing or bending.
3Strength
If the lead frame is made more rigid to prevent bending during molding, then deformation is reduced, but the flexibility needed for assembly and potential thermal expansion is reduced
Solution Approach 1:
The support structure is segmented through the substrate design, which provides rigid support only at specific locations where pads are present and deformation is most critical. The substrate does not rigidly constrain the entire lead frame, allowing other portions to maintain their flexibility for assembly and thermal expansion. This segmentation approach provides targeted rigidity without sacrificing overall adaptability.
Data Source
AI summary
Microelectronic devices and methods for manufacturing microelectronic devices are disclosed herein. One such method includes forming a plurality of apertures in a substrate with the apertures arranged in an array, and, after forming the apertures, attaching the substrate to a lead frame having a plurality of pads with the apertures in the substrate aligned with corresponding pads in the lead frame. Another method includes providing a partially cured substrate, coupling the partially cured substrate to a plurality of leads, attaching a microelectronic die to the leads, and electrically connecting the microelectronic die to the leads.