Lead Frame Recess Filling for Debris-Free Saw Singulation
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Solution Overview
Problem
During the saw singulation process of flat-pack no-lead semiconductor device packages, copper debris accumulates in the recesses of wettable flanks, leading to visual rejection and increased risk of defects in solder joints due to the ductile nature of copper, which fills and peels off, causing burrs and tear-outs, and existing methods like punch singulation or specialized blades do not fully eliminate debris accumulation.
Innovation Solution
Filling the depressions in the lead frames with a wettable material or a removable material before singulation to prevent debris accumulation, ensuring a debris-free recess and facilitating clean saw singulation, which can be either a solder wettable material like SAC305 or a removable material like a hot-water soluble adhesive that is easily rinsed away after singulation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If saw singulation is used to cut through the strip between lead frames, then productivity is improved, but copper debris accumulates in the recesses of wettable flanks due to the ductile nature of copper
Solution Approach 1:
The recesses are pre-filled with a material before the saw singulation process. This preliminary action prevents copper debris from accumulating in the recesses during cutting, as the filling material occupies the space and prevents debris entrapment while allowing the saw to cut efficiently
Solution Approach 2:
An intermediary material is introduced into the recesses to mediate between the copper lead frame and the saw blade. This material prevents direct contact between the copper and the saw, eliminating the harmful effect of copper debris accumulation while maintaining the structural integrity of the lead frame
2Object-generated harmful factors
If punch singulation is used instead of saw singulation to avoid copper debris, then debris accumulation is reduced, but the number of individual units on a strip is limited
Solution Approach 1:
The recesses are pre-filled with material before singulation, enabling the use of saw singulation (which allows higher productivity) without suffering from the copper debris accumulation problem. This preliminary filling action resolves the contradiction by allowing the high-productivity saw method to be used while preventing the harmful debris effect
3Object-generated harmful factors
If specialized blades are used to reduce debris during saw singulation, then some debris is reduced, but debris accumulation in recesses is not fully eliminated
Solution Approach 1:
Instead of modifying the saw blade to reduce debris, the recesses are pre-filled with material before cutting. This approach is simpler than developing specialized blades and completely prevents debris accumulation by occupying the recess space before the cutting process begins
Solution Approach 2:
The filling material serves as an intermediary that completely prevents copper debris from entering the recesses, providing a more effective solution than specialized blades which only reduce but do not eliminate debris accumulation
4Reliability
If the recess is made small to improve solder joint formation, then solder wetting is improved, but debris accumulation becomes more apparent and harmful
Solution Approach 1:
The recesses are pre-filled with material before singulation, preventing copper debris from accumulating even in small recesses. This allows the recesses to be made small for improved solder joint formation without the compounding problem of visible and harmful debris accumulation
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 method prevents the formation and accumulation of burrs and debris during singulation, allowing for the production of debris-free recesses, especially in fine pitch leads, and enhances the formation of inspectable solder joints by maintaining a clean and supported surface for solder wetting during assembly.
Implementation Method 1
Filling the depressions in the lead frames with a wettable material or a removable material before singulation to prevent debris accumulation
Implementation Method 2
a removable material like a hot-water soluble adhesive that is easily rinsed away after singulation
Implementation Method 3
Surface tension causes the solder to wet up into the recess of the wettable flank, and the solder may advantageously form a fillet
Implementation Method 4
solder can wet to the recess
Data Source
Figure 1~3
Figure 4~6
Figure 7
AI summary
A structure and method to improve saw singulation quality and wettability of integrated circuit packages (140) assembled with lead frames (112) having half-etched recesses (134) in leads. A method of forming a semiconductor device package includes providing a lead frame strip (110) having a plurality of lead frames. Each of the lead frames includes a depression (130) that is at least partially filled with a material (400) prior to singulating the strip.