Semiconductor Lead Chamfering for Stronger DFN Solder Bonds
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Solution Overview
Problem
Conventional DFN packages face challenges in ensuring sufficient bonding strength and reliability between leads and mounting substrates due to low solder wettability and stress concentration at the corner portions of leads, leading to reduced bonding area and potential cracks.
Innovation Solution
The semiconductor device incorporates leads with a chamfering portion at the corner between the lower surface and end face, and a metal film with good solder wettability is applied to the lead surfaces, including the chamfering portion, to facilitate better solder adhesion and distribute thermal stress evenly.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the lead end faces are exposed through cutting with a dicing device, then the lead material is exposed as is, but it is difficult to form sufficient fillets on the lead end faces when the lead material has low solder wettability
Solution Approach 1:
The patent applies a plating layer specifically at the corner portion between the lower surface and end face of the lead, creating a localized region with enhanced solder wettability. This local quality change allows the lead material to have different properties at different locations, with the plated corner portion providing improved bonding characteristics while the rest of the lead maintains its original material properties.
Solution Approach 2:
The plating layer is formed in advance on the corner portion of the lead before the bonding process. This preliminary action ensures that the surface with good solder wettability is already prepared and positioned correctly, enabling reliable fillet formation during subsequent bonding operations without requiring additional steps during assembly.
2Ease of manufacture
If only the lower surface of the lead with a plating layer is bonded to the mounting substrate, then the bonding area decreases, but this may result in reduced bonding strength between the leads and the mounting substrate
Solution Approach 1:
The plating layer is strategically positioned at the corner portion of the lead rather than covering the entire lower surface. This localized plating creates an optimal bonding region that concentrates bonding strength at the critical corner area where stress concentration occurs, while maintaining ease of bonding process.
3Reliability
If a plating layer is formed in a concave portion at the corner portion between the lower surface and end face of the lead, then bonding reliability is improved, but the device complexity increases
Solution Approach 1:
The plating layer is applied specifically to the corner portion of the lead, creating a localized region with enhanced properties. This approach improves bonding reliability at the critical stress concentration point without requiring complex structural modifications to the entire lead assembly.
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 design enhances bonding reliability by allowing easier formation of fillets on lead ends and reduces stress concentration, thereby improving the connection strength and durability of the semiconductor device.
Implementation Method 1
a metal film with good solder wettability is applied to the lead surfaces, including the chamfering portion
Data Source
AI summary
A semiconductor device includes a semiconductor chip, a plurality of leads arranged apart from each other around the semiconductor chip in a plan view and extending from the semiconductor chip side, and an encapsulating resin forming an outer shape such that at least lower surfaces and end faces of the plurality of leads are respectively exposed, and the lead includes a lead main body portion positioned on the semiconductor chip side, having a first end face formed in an extending direction, and having a chamfering portion at a corner portion between a lower surface and the first end face, and a lead outer end portion extending from the first end face, having an upper surface that is coplanar with the lead main body portion, being thinner than the lead main body portion, and on which a second end face is formed.