Data processing: generic control systems or specific application – Specific application – apparatus or process – Mechanical control system
Reexamination Certificate
1998-01-26
2003-03-25
Gordon, Paul P. (Department: 2125)
Data processing: generic control systems or specific application
Specific application, apparatus or process
Mechanical control system
C700S281000, C700S283000, C073S30400R
Reexamination Certificate
active
06539286
ABSTRACT:
BACKGROUND
The invention relates to a fluid level sensor positioned in a container that dispenses fluid used in forming electronic devices.
In the exemplary manufacturing process of electronic devices, different types of materials are used. For example, adhesives are commonly used to attach one component of a device to another component. To make an integrated circuit device, a die is mounted to a support structure by means of adhesives, which can be one of several types, including metal alloys (e.g., solder) and organic or inorganic adhesives (e.g., epoxies and polyimides, which can be filled with metal).
In the integrated circuit device
10
shown in
FIG. 1
, a die
14
can be mounted to a leadframe
12
by using an adhesive layer
16
to attach the underside
34
of the die
14
to the top surface
30
of leadframe
12
. If an epoxy or polyimide type adhesive is used, the adhesive is typically dispensed in fluid form onto portions of the top surface
30
of the leadframe
12
. After formation of the adhesive layer
16
, the die
14
is contacted to the adhesive layer
16
to bond the die
14
to the leadframe
12
. Next, bond pads
24
on the die
14
are wirebonded (using wires
26
) to corresponding bond pads
22
on leadfingers
20
of the leadframe
12
. The leadframe/die assembly is then encapsulated using an encapsulant
18
(e.g., plastic).
An adhesive originally in fluid form is dispensed onto a target support structure, such as the leadframe
12
in
FIG. 1
, using a dispensing container in a die attach machine. Various automated methods have been used to detect the level of the fluid adhesive inside the dispensing container. One method that has been used is magnetic sensing. The dispensing container includes a ferromagnetic coated piston that sits on top of the fluid adhesive. As the adhesive is being dispensed, the level of the fluid decreases, and the ferromagnetic piston falls inside the cylindrical container with the fluid level. When the ferromagnetic coated piston reaches a predetermined position in the container, it activates a magnetic sensor to stop the die attach machine. However, certain types of adhesives contain ferromagnetic fillers that may interfere with the magnetic sensing mechanism.
Various fluid level sensors and detectors have been proposed to detect different types of fluid (e.g., gasoline, water, oil) stored in different types of containers. Such sensors include optical sensors and electrical sensors.
SUMMARY
Generally, the invention is directed to a sensor used in a fluid dispensing container, the sensor including a pair of electrical conductors positioned in the dispensing container to which a voltage to detect the amount of fluid in the container.
The invention has one or more of the following advantages. Accurate sensing of the fluid level in a fluid dispensing container can be performed with a large variety of adhesives, including adhesives filled with a ferromagnetic filler. The fluid level sensing can be accomplished without the use of moving parts inside the container, which improves reliability and facilitates handling.
In general, in one aspect, the invention features a system for dispensing an adhesive onto an electronic device. The system includes a container storing the adhesive and a port through which the adhesive can flow. Electronic conductors are positioned in the container. A voltage is applied across the conductors so that a current flow is induced through the adhesive in the container. The current is measured to determine a level of the adhesive in the container.
In general, in another aspect, the invention features a method of applying an adhesive onto an electronic device. The adhesive is stored in a container having electrical conductors positioned in the container. A voltage is applied across the conductors. The current flow through the adhesive is measured to determine the adhesive level in the container. The adhesive is supplied to the electronic device until the adhesive level drops below a predetermined amount.
Other features and advantages will become apparent from the following description and from the claims.
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Gordon Paul P.
Micro)n Technology, Inc.
Trop Pruner & Hu P.C.
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