Optics: measuring and testing – By configuration comparison – With object being compared and scale superimposed
Reexamination Certificate
2000-07-14
2002-04-30
Pham, Hoa Q. (Department: 2877)
Optics: measuring and testing
By configuration comparison
With object being compared and scale superimposed
C033S201000, C359S801000, C359S804000
Reexamination Certificate
active
06381016
ABSTRACT:
BACKGROUND OF THE INVENTION
Semiconductor devices are generally packaged in an integrated circuit (IC) package. A typical IC package
10
is shown in FIG. I. The IC package
10
consists of a leadframe
20
and a die
30
encapsulated in a housing
40
, such as molded plastic or resin. The leadframe
20
includes a support, called a die pad
50
, on which the die
30
is mounted, and a plurality of leads
60
electrically coupled to the die
30
. The leads
60
are connected to bond pads
70
on the die
30
via wire bonds
80
. The leads
60
electrically connect the die
30
to the circuitry external to the package (not shown).
During packaging, a bonding material is used to adhere the die
30
to the die pad
50
, and wires
80
are bonded to electrically couple the leads
60
of the leadframe
20
to the bond pads
70
on the die
30
. Then the leadframe
20
and die
30
assembly is placed in a mold, and a molten insulating material, such as plastic resin, is added to the mold and cured. The result is an IC package that consists of the die
30
and a portion of the leadframe
20
encapsulated in insulating housing
40
, such that the end portions of the leads
60
extend from the housing
40
.
During IC package manufacturing, the leadframes typically are inspected to ensure that the lead widths are acceptable. Lead width inspection is a quality control activity that involves measuring the width of the leads and comparing the measured lead widths to predetermined specifications. One method of inspecting a lead frame entails placing the IC packages under a microscope, measuring the lead widths, and comparing the measurements to the pre-determined specification limits. If a lead width is within the range of the specification limits, then it is deemed acceptable. If a lead width is not within the range of the specification limits, then it is rejected. This process requires a skilled operator, up to 5 minutes or more per inspection, and is susceptible to errors in the readings. Thus, the current systems and methods of lead width inspection is labor intensive, prone to inaccuracies, and slow. Systems and methods of improving the speed, accuracy and simplicity of lead width inspection are needed.
SUMMARY OF THE INVENTION
The present invention comprises lead inspection systems, methods, and templates. The templates include upper and lower specification limits marked on the template to form a lead width guide. To inspect a leadframe, a user places a leadframe on the template, lines up the leads on the leadframe with an alignment mark, and looks to see if the leads fall within the lead width guide marked on the template. If the leads fall within the lead width guides, then the lead width is acceptable. If the leads do not fall within the lead width guides, the lead width is unacceptable. Because of the small size of the leadframes, typically, the leadframe is inspected with a microscope. The templates may be placed in the eye piece of a microscope, and provide a single instrument for rapidly inspecting lead widths. Since the templates replace the error prone and tedious task of measuring the lead widths with a simple visual inspection, the systems and methods of the present invention improve the speed, accuracy, and simplicity of lead width inspection, thus, overcoming the limitations and shortcomings of the prior art.
In accordance with one aspect of the present invention a template for inspecting leadframes is provided. The template includes a first specification limit and a second specification limit. The first specification limit is positioned a distance from the second specification limit so as to form a lead width guide therebetween. The template may further include an alignment mark positioned a second distance from the lead width guide so as to provide a guide for aligning a portion of the leadframe with the lead width guide. The template may be a substantially optically clear material with the first and second specification limits indicated by dark lines on the substantially optically clear material. The clear material may be any substantially optically clear material, such as plastic or glass. The template may be coupled to a leadframe viewer, such as an eyepiece of a microscope, forming a leadframe viewing assembly.
The microscopes utilized in the present invention include those microscopes capable of 3- inspection. The present invention may be utilized to inspect the leadframes of any type of IC package, such as plastic dual in-line packages, small outline packages, plastic leaded chip carriers, quad flat packages, or any other type of IC packages. The templates of the present invention may have one or a plurality of lead width guides associated therewith.
In accordance with another aspect of the invention, a system for inspecting a leadframe is provided. The system may include an imaging device, such as a microscope, and a template. The template may be coupled to the imaging device so as to produce an image of the template, for instance by coupling the template to at least one eyepiece of the microscope. The template may have one or more lead width guides formed by a first specification limit positioned a distance from a second specification limit. The template may further include one or more alignment marks positioned a second distance from a corresponding lead width guide so as to provide a guide for aligning a portion of the leadframe with the lead width guide. The template may be a substantially optically clear material with the first and second specification limits indicated by dark lines on the substantially optically clear material. The clear material may be any substantially optically clear material, such as plastic or glass.
In accordance with yet another aspect of the present invention, a method for inspecting a leadframe is provided. The method includes providing a template, imaging one or more portions of the leadframe and the template, and comparing the one or more portions of the leadframe to the one or more lead width guides of the template. The template may be coupled to an eyepiece of the microscope, and the template and the one or more portions of the leadframe may be imaged by a microscope. The one or more portions of the leadframe may be compared to the one or more lead width guides by visual inspection. The method may further include determining if the one or more portions of the leadframe are of an acceptable width.
The template may have one or more lead width guides formed by a first specification limit and a second specification limit. The template may further include one or more alignment marks positioned a second distance from a corresponding lead width guide so as to provide a guide for aligning a portion of the leadframe with the lead width guide. The template may be a substantially optically clear material with the first and second specification limits indicated by dark lines on the substantially optically clear material. The clear material may be any substantially optically clear material, such as plastic or glass.
To the accomplishment of the foregoing and related ends, the invention comprises the features hereinafter fully described and particularly pointed out in the claims. The following description and the annexed drawings set forth in detail certain illustrative embodiments of the invention. These embodiments are indicative, however, of but a few of the various ways in which the principles of the invention may be employed. Other objects, advantages, and novel features of the invention will become apparent from the following detailed description of the invention when considered in conjunction with the drawings.
REFERENCES:
patent: 3398631 (1968-08-01), McGivern et al.
patent: 4078864 (1978-03-01), Howell
patent: 4172662 (1979-10-01), Vogel
patent: 4855928 (1989-08-01), Yamanaka
patent: 5155556 (1992-10-01), Foanio
patent: 5485398 (1996-01-01), Yamazaki et al.
patent: 5933239 (1999-08-01), Hoshiyama
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