Leaded Semiconductor Package Wirebonding to Reduce Lead Mold Flash
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Solution Overview
Problem
Conventional wirebonding techniques can cause lead lifting during tail cutting, resulting in mold flash on semiconductor package leads due to strong adhesion between bond wires and leads, which affects solder profile and electrical conductivity.
Innovation Solution
The reverse bond wire process involves cutting the bond wire over the bond pad instead of the lead, forming a second ball bond on the lead, and then paying out the wire to form a loop and stitch bond, reducing the upward tension on the lead and minimizing lead deformation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional tail cutting over the lead is used, then wire bonding connection is formed, but lead lifting occurs causing mold flash
Solution Approach 1:
The patent inverts the conventional wire bonding sequence by performing tail cutting over the bond pad instead of over the lead. This reversal eliminates the upward tension on the lead that causes lead lifting and subsequent mold flash, while still achieving reliable wire bonding connections through the alternative cutting location.
2Strength
If strong adhesion between bond wires and leads is achieved, then electrical connection is improved, but lead lifting during tail cutting increases
Solution Approach 1:
The patent extracts the tail cutting operation from its conventional location over the lead and relocates it to over the bond pad. This separation removes the harmful effect of upward tension on the lead while preserving the strong adhesion between bond wires and leads, as the cutting occurs at a location that does not impose tensile stress on the lead.
3Productivity
If mold flash is present on leads, then packaging is complete, but solder profile and electrical conductivity are affected
Solution Approach 1:
The patent applies preliminary anti-action by preventing lead lifting at the wire bonding stage through inverted tail cutting. This proactive measure eliminates the root cause of mold flash formation, thereby preventing subsequent soldering defects before they occur, rather than addressing them after packaging is complete.
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 significantly reduces mold flash on leads, improving yield by almost eliminating lead mold flash issues and allowing for the omission of deflash processing, thereby enhancing the reliability of semiconductor packages.
Implementation Method 1
a combination of heat, pressure, and ultrasonic vibration is used to cause the ball to adhere to the surface of the bond pad
Implementation Method 2
a ball is formed on the exposed end of the wire using an electronic flame off (EFO) mechanism
Data Source
AI summary
A semiconductor package includes a leadframe including a die pad and a plurality of leads including a first lead, wherein the first lead includes a first ball bond. A semiconductor die having a plurality of bond pads including a first bond pad is on the die pad including a second ball bond on the first bond pad and a stitch bond on the second ball bond. A first wirebond connection is between the first ball bond and the stitch bond.