Non-Leaded Package Structure with Preformed Solder Layer
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Solution Overview
Problem
Existing quad or dual flat non-leaded (QFN or DFN) package structures face limitations in increasing lead density and sustaining bonding strength between leads and encapsulants, which hinders their applicability and manufacturing convenience, especially for high-frequency signal transmission applications.
Innovation Solution
A non-leaded package structure with protruding leads and a preformed solder layer on the lower surfaces, where the solder layer serves as a shield and simplifies the surface mount technology (SMT) process by being formed in recess patterns on the metal base plate before back etching, allowing leads to protrude out of the encapsulant with the solder layer coating, thereby enhancing manufacturing reliability and convenience.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the density of leads is increased to meet higher capabilities requirements, then the package capability is improved, but the bonding strength between leads and encapsulant deteriorates
Solution Approach 1:
A solder layer is pre-formed on the leads before encapsulation. This preliminary action ensures that the leads have adequate bonding material available before the encapsulation process, thereby maintaining bonding strength even when lead density is increased and leads are more closely spaced.
Solution Approach 2:
The invention changes the physical and chemical parameters of the lead surface by forming a solder layer on it. This parameter change (adding a solder coating) improves the bonding characteristics of the leads with the encapsulant, allowing for higher lead density without sacrificing bonding strength.
2Strength
If additional solder application steps are added to ensure bonding strength, then the bonding strength is improved, but the manufacturing complexity increases
Solution Approach 1:
The formation of the solder layer on the leads is merged with the encapsulation process. The encapsulant material itself serves as the vehicle for delivering the solder layer to the leads, combining two functions (encapsulation and solder application) into a single integrated process step.
Solution Approach 2:
The encapsulant material performs multiple functions: it provides mechanical protection, electrical insulation, and serves as a vehicle for delivering the solder layer to the leads. This multi-functionality eliminates the need for separate solder application steps, reducing manufacturing complexity while ensuring adequate bonding strength.
3Ease of operation
If leads are made to protrude out of encapsulant for surface mount application, then the surface mount ability is improved, but the manufacturing reliability deteriorates
Solution Approach 1:
The solder layer is pre-formed on the leads before encapsulation, ensuring that when leads protrude from the encapsulant, they already have the necessary solder material for reliable surface mount attachment. This preliminary preparation eliminates the need for additional solder application steps and ensures consistent results.
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
The preformed solder layer acts as a shield for the leads, simplifies the surface mount application process, and increases the bonding strength between the leads and the encapsulant, improving the reliability and convenience of the manufacturing process by eliminating the need for additional solder application.
Implementation Method 1
a back etching process is performed on the lower surface of the metal base plate with the first solder layer serving as an etch mask to partially remove the metal base plate
Implementation Method 2
The solder layer therein not only can serve as a shield layer for the leads
Implementation Method 3
A plurality of bonding wires are formed for electrically connecting the chip to the first protruding parts respectively
Data Source
AI summary
A manufacturing method of a non-leaded package structure is provided. An upper surface and a lower surface of a metal base plate are patterned so as to form a plurality of first protruding parts and at least a second protruding part on the upper surface and to form a plurality of first recess patterns on the lower surface corresponding to the first protruding parts. A first solder layer is formed in each of the first recess patterns respectively. A chip is mounted on the second protruding part and electrically connected to the first protruding parts with a plurality of bonding wires. An encapsulant is formed on the upper surface. A back etching process is performed on the lower surface to partially remove the metal base plate until the encapsulant is exposed and a lead group including at least a die pad and a plurality of leads is defined.