Solder Paste Dispensing Device With Buffer Chamber for Consistent Dot Sizes
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Solution Overview
Problem
Existing dispensing devices struggle to maintain consistent solder dot sizes due to the shear-thinning nature of solder pastes, despite high-quality compressed air sources and solenoid valves, compromising semiconductor assembly quality.
Innovation Solution
Incorporation of a buffer chamber and an elongated sealing element in the dispensing device to control the dispensing process in two steps, filling the buffer chamber first and then emptying it onto the work piece, independent of viscosity and pressure variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a Time-Pressure dispensing valve is used with high-quality compressed air sources and solenoid valves, then the dispensing control is improved, but the consistency of solder dot sizes deteriorates due to the shear-thinning nature of solder pastes
Solution Approach 1:
The dispensing system is segmented into two independent parts: a reservoir for holding solder paste and a buffer chamber for metering the dispensed amount. The elongated sealing element divides the flow path into separate segments (reservoir-to-buffer and buffer-to-nozzle), allowing independent control of each segment. This segmentation isolates the viscosity variations in the reservoir from the precision metering function in the buffer chamber.
Solution Approach 2:
The buffer chamber acts as an intermediary between the reservoir and the dispensing nozzle. It receives solder paste from the reservoir, isolates it from further viscosity changes, and then meters a precise volume to the nozzle. The elongated sealing element serves as a mechanical intermediary that sequentially opens and closes to control the transfer of paste between chambers, ensuring consistent metering independent of reservoir pressure variations.
2Manufacturing precision
If the dispensing valve-on time and pressure are strictly controlled, then the dispensing process is improved, but the sensitivity to viscosity variations increases
Solution Approach 1:
The buffer chamber is pre-filled with a specific volume of solder paste before dispensing begins. This preliminary action of filling the buffer chamber isolates the metering function from subsequent viscosity variations in the reservoir. The elongated sealing element ensures that once the buffer is filled, the dispensing operation draws from this pre-measured volume, making the process insensitive to later viscosity changes.
Solution Approach 2:
The invention changes the controlling parameter from time-pressure control to volume control. By using the buffer chamber's fixed volume and the elongated sealing element's positional control, the system transitions from controlling dispensing through time and pressure parameters to controlling it through geometric volume parameters, which are inherently more stable against viscosity variations.
3Manufacturing precision
If an elongated sealing element and buffer chamber are added to control dispensing in two steps, then the solder dot size consistency is improved, but the device complexity increases
Solution Approach 1:
The buffer chamber serves multiple functions: it acts as a volume meter, a pressure isolator, and a flow regulator. The elongated sealing element performs multiple roles by sequentially blocking different passages: it controls the fill operation, then the dispense operation, and finally the purge operation, all with a single component. This multi-functionality reduces the need for additional separate valves and control mechanisms.
Solution Approach 2:
The elongated sealing element is nested within the valve body structure, with its seals positioned to interact with different passages at different times. The buffer chamber is nested within the overall dispensing device architecture, integrating the metering function into the existing valve structure rather than adding a completely separate external device.
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
Ensures precise and consistent solder dot sizes by controlling the dispensed volume through the buffer chamber's volume and the position of the elongated sealing element, reducing reliance on viscosity and pressure stability.
Implementation Method 1
The fluid dynamics of solder paste within the TP dispensing valve can be modelled as viscous laminar pipe flow, justified by the low Reynolds Number, indicative of laminar flow characteristics.
Implementation Method 2
Transitioning to the ON state involves the elevation of the spool to the 'up' position, coupled with the concurrent application of compressed air to the piston by the controller. This process exerts pressure on the solder paste within the syringe, facilitating its controlled dispensing onto the target object.
Data Source
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AI summary
A dispensing device arranged for dispensing solder paste, said dispensing device comprising a dispensing reservoir arranged for containing said solder paste, a channel arranged for receiving, at an inlet thereof, said solder paste from said dispensing reservoir and for dispensing said solder paste at an outlet thereof, an elongated sealing element positioned in said channel, a buffer chamber arranged for buffering solder paste, wherein said buffer chamber is connected to said channel, wherein said elongated sealing element is arranged to provide a passageway between said dispensing reservoir and said buffer chamber in a closed state and arranged to provide a passageway between said buffer chamber and said outlet of said channel in an opened state.