Recessed Die Pad Structure for Semiconductor Die Alignment
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Solution Overview
Problem
During semiconductor chip manufacturing, unbalanced wetting forces caused by non-uniform heat transfer during the reflow process can lead to undesired lateral rotation or translation of semiconductor dies on die pads, resulting in misalignment and misplacement, which complicates subsequent electrical coupling operations.
Innovation Solution
Die pads with a recessed design are used to constrain the movement of semiconductor dies, ensuring proper alignment and positioning through the use of a solder fillet that extends along the outer perimeter of the die, maintaining the die within the recess even under unbalanced wetting forces during the reflow process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a conventional flat die pad design is used, then the manufacturing process is simple, but unbalanced wetting forces during reflow cause lateral rotation or translation of semiconductor dies resulting in misalignment and misplacement
Solution Approach 1:
The die pad structure is segmented into multiple functional zones: a recessed region for die placement, a raised region for solder fillet formation, and a barrier region to contain excess solder. This segmentation allows each zone to perform its specific function independently, improving die alignment precision while managing the increased structural complexity through clear functional division.
Solution Approach 2:
The invention transitions from a conventional two-dimensional flat die pad surface to a three-dimensional structured surface with recesses, raised portions, and controlled depth variations. This dimensional change creates physical constraints that guide die placement and prevent lateral movement during reflow, thereby improving alignment precision.
2Manufacturing precision
If the die pad surface is made uneven with recesses and raised portions, then die placement precision is improved, but the manufacturing process becomes more complex
Solution Approach 1:
The die pad structure with recesses and raised portions is pre-formed before the reflow process. This preliminary structuring ensures that when solder paste is applied and reheated, the molten solder naturally flows into the recessed areas and is contained by the raised portions, guiding die placement without requiring complex real-time control during manufacturing.
Solution Approach 2:
The uneven die pad surface structure serves itself by using the geometry of recesses and raised portions to automatically guide solder flow and die placement. The structure leverages gravity and surface tension of the molten solder to achieve proper die positioning and solder fillet formation without additional external intervention or complex manufacturing steps.
3Manufacturing precision
If a recessed die pad design is used to constrain die movement, then die alignment is improved, but the risk of solder short circuits between adjacent dies increases
Solution Approach 1:
The die pad is segmented into individual recessed regions for each die, separated by raised barrier portions. This segmentation physically isolates the solder fillets for adjacent dies, allowing each die to have its own contained solder volume. This prevents solder from adjacent dies from merging and causing short circuits, while still providing the alignment benefits of the recessed structure.
Solution Approach 2:
The raised barrier portions between adjacent recesses act as intermediary structures that physically separate and contain the solder fillets. These intermediary raised portions prevent direct contact between solder from neighboring dies, eliminating the short circuit risk while allowing the recessed regions to maintain precise die alignment.
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 configuration effectively reduces instances of die misalignment and facilitates even distribution of components within the mold compound, enhancing the reliability and efficiency of the semiconductor package manufacturing process.
Implementation Method 1
unbalanced wetting forces caused by non-uniform heat transfer during the reflow process can lead to undesired lateral rotation or translation of semiconductor dies on die pads
Implementation Method 2
a solder fillet engaged within the recess and with the outer perimeter of the semiconductor die, wherein the solder fillet extends from a bottom surface of the recess to a point along the outer perimeter that is spaced from 1 millimeter (mm) to 2.5 mm from the bottom surface of the recess
Data Source
AI summary
In some examples a semiconductor chip package includes a conductive terminal. In addition, the semiconductor chip package includes a die pad including a top side and a recess extending into the top side. The die pad is downset relative to the conductive terminal. Further, the semiconductor ship package includes a semiconductor die positioned within the recess, wherein the semiconductor die has an outer perimeter, and a solder fillet engaged within the recess and with the outer perimeter of the semiconductor die. Still further, the semiconductor chip package includes a wire bond coupled to the semiconductor die and the conductive terminal, and a mold compound covering the conductive terminal, the wire bond, the die pad, and the semiconductor die.