U.S. patent application number 10/090083 was filed with the patent office on 2003-05-08 for method of testing bonded connections, and a wire bonder.
Invention is credited to Farassat, Farhad.
Application Number | 20030085255 10/090083 |
Document ID | / |
Family ID | 8179190 |
Filed Date | 2003-05-08 |
United States Patent
Application |
20030085255 |
Kind Code |
A1 |
Farassat, Farhad |
May 8, 2003 |
Method of testing bonded connections, and a wire bonder
Abstract
Method of testing wire-bond connections between a bonding wire
and a substrate surface, which are produced by a bonding head with
a bonding tool and a wire clamp associated with the bonding tool,
under pressure and the action of ultrasound and/or heat, wherein
after the bonded connection has been created, the bonding head or
the bonding tool is raised a short distance away from the bonding
site, the bonding wire is firmly gripped by the wire clamp, and the
bonding head or the wire clamp with bonding wire gripped therein is
raised for a second distance, during which process the tensile
force acting on the bonding wire is detected.
Inventors: |
Farassat, Farhad;
(Taufkirchen, DE) |
Correspondence
Address: |
KNOBBE MARTENS OLSON & BEAR LLP
2040 MAIN STREET
FOURTEENTH FLOOR
IRVINE
CA
92614
US
|
Family ID: |
8179190 |
Appl. No.: |
10/090083 |
Filed: |
March 1, 2002 |
Current U.S.
Class: |
228/103 ;
228/110.1 |
Current CPC
Class: |
H01L 2224/859 20130101;
H01L 2924/01068 20130101; B23K 31/12 20130101; H01L 2224/78301
20130101; H01L 2924/14 20130101; B23K 20/005 20130101 |
Class at
Publication: |
228/103 ;
228/110.1 |
International
Class: |
B23K 031/12 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 7, 2001 |
EP |
01 126 621.0 |
Claims
1. Method of testing wire-bond connections between a bonding wire
and a separate surface, which are produced by a bonding head with a
bonding tool and a wire clamp associated with the bonding tool,
under pressure and the action of ultrasound and/or heat,
characterized in that after the bonded connection has been created,
the bonding head or the bonding tool is lifted a short distance
away from the bonding site, the bonding wire is fixedly gripped by
the wire clamp, and the bonding head or the wire clamp with bonding
wire gripped therein is raised for a second distance, during which
process the tensile force acting on the bonding wire is
detected.
2. Testing method according to claim 1, characterized in that the
bonding head or the wire clamp is raised for a second distance
calculated, in dependence on the structural features, so that a
predetermined tensile force is exerted as a result of the raising,
and an intact state of the bonded connection is detected during
raising.
3. Testing method according to claim 2, characterized in that the
intactness of the bonded connection is determined by observing the
time course of the tensile force acting on the wire clamp during
the raising.
4. Wire bonder in which there is integrated into a bonding head a
testing arrangement for wire-bond connections between a bonding
wire and a separate surface, in particular a bonding pad.
5. Wire bonder according to claim 4, with a bonding head that
comprises a tool or transducer holder to hold a bonding tool and a
wire-clamp holder to hold a wire clamp for gripping a bonding wire,
as well as a drive mechanism for the vertical displacement of the
bonding head or tool holder and wire-clamp holder, characterized in
that a program control system to control a predetermined movement
sequence of the bonding head or tool holder and wire-clamp holder
is associated with the drive mechanism in order to carry out a
measurement of tensile force at the bonding wire, and a
force-measuring device is associated with the wire-clamp holder in
order to measure a tensile force acting on a bonded connection to
the bonding wire that has been produced.
6. Wire bonder according to claim 5, characterized in that the
wire-clamp holder is mounted on the bonding head so that it can be
elastically deflected or linearly displaced against the action of a
pretensioning element, and a force-measurement element, in
particular a strain gauge, is associated with the holder.
7. Wire bonder according to claim 6, characterized in that the
wire-clamp holder comprises a weakened preferential bending section
or leaf-spring section, which ensures the elastic deflectability
and in which the strain gauge is located.
8. Wire bonder according to claim 5, characterized in that within
the program control system a control program for automatically
carrying out the method according to one of the claims 1 to 3 is
implemented.
Description
DESCRIPTION
[0001] The invention relates to a method of testing bonded
connections and to a wire bonder equipped with a corresponding,
integrated testing arrangement.
[0002] Wire bonding is a method in which electrical connections of
semiconductor components are produced by means of fine metal wires.
With wire-bond connections, for example, the contact surfaces of
discrete components can be electrically connected to one another,
or integrated circuits to contact surfaces on the associated
housing or, in the case of hybrid circuits, inserted monolithic
elements can be electrically connected to the thick-film circuitry
into which they have been inserted.
[0003] In the course of the development of technology for
connecting semiconductor components and circuits, various bonding
methods have been invented and a large number of bonding machines
suitable for this purpose have been proposed. The most commonly
used wire-bonding methods are ultrasound (U/S) bonding,
thermal-compression (T/C) bonding, and thermosound (T/S) bonding.
Wire bonders to implement these methods guide a bonding wire to the
point (bond pad) provided for the purpose of creating the bonded
connection, and then by means of a bonding tool, for instance in
the form of a capillary, wedge or nailhead, the wire is deformed
and fixed in place by application of a compressive force and the
supplementary action of oscillatory and/or thermal energy. In this
process, a kind of welded connection is formed between the bonding
wire and the bond pad.
[0004] The quality of the bonded connection is crucial for the
functionality and reliability of the electronic components
constructed by employing the bonding method. Therefore it is
desirable, if not indispensable, for the parameters of the bonding
process to be monitored while the process is under way, as well as
for the quality of the finished bonded connection to be tested.
Various solutions to the problem of monitoring and regulating
essential parameters of the ongoing bonding process--in particular
the bonding force and where appropriate also the ultrasound
amplitude or energy--have been proposed.
[0005] In the U.S. Pat. No. 4,854,494 a wire bonder is described
that comprises means for monitoring several bonding parameters,
especially the bonding force and ultrasound amplitude. This wire
bonder has a tool holder with a weakened section, where bowing can
occur when the tool is used to press the bonding wire onto the bond
pad. By way of a strain gauge disposed in this weakened section,
the momentary bonding force is detected and can be kept at a
predetermined set point by way of a downstream regulation
system.
[0006] The U.S. Pat. No. 5,230,458 likewise describes a bonding
head with a force sensor that measures the compressive force
exerted by the bonding tool and signals it to a real-time control
circuit. The latter sends an adjustment signal to an actuator that
causes a movement in the Z direction, to adjust the bonding force.
The bonding machine described here is an ultrasonic bonder of the
capillary type, in which the ultrasound transmitter, with capillary
attached to serve as bonding tool, is mounted on a carrier frame.
This frame also carries an extension arm to guide the bonding wire,
which is disposed above another extension arm bearing the
ultrasound transmitter.
[0007] In the applicant's patent GB 2 270 868 A a wire-bonding
method and system of a different type is described, namely the
ultrasonic (U/S) wedge bonder, in which likewise provision is made
for the detection and continuous regulation of bonding force and
ultrasonic energy. For this purpose, the deformation of the bonding
wire is monitored.
[0008] The applicant's patent EP 0 857 535 A1 describes a bonding
head with two extension arms, the first of which (tool holder)
carries the bonding tool while the second (wire-clamp holder),
disposed above the first, carries a wire clamp to grasp a bonding
wire and fix it in position. Here, again, the bonder is of the U/S
wedge type. The bonding force is adjusted by the action of a linear
motor in combination with a pretensioning spring, in response to
the signal of a piezo detector disposed at the end of the tool
holder.
[0009] Moreover, a known method of testing bonded connections is to
exert a tensile force with a predetermined value on the attached
bonding wire. If the bonded connection withstands this tensile
force, it is judged to be qualitatively perfect. This test is
carried out as a procedure following the manufacturing process.
[0010] It is the objective of the invention to disclose a method of
testing bonded connections that is directly integrated into the
manufacturing process, as well as a wire bonder suitable for
implementing this method, which enables real-time quality control
and the immediate execution of quality-ensuring adjustment
procedures while the bonding process is still under way.
[0011] This objective is achieved with respect to the method by a
testing procedure with the characteristics given in claim 1, and
with respect to the apparatus by a wire bonder with the
characteristics given in claim 4.
[0012] The invention includes the essential idea of exposing a
bonded connection to a tensile force immediately after it has been
created, and of detecting its response. It further includes the
idea that for this purpose the bonding tool and a wire clamp to
grip the bonding wire should be moved in a suitable sequence of
steps, in combination with a step in which the tensile force is
measured, and the idea of disclosing a corresponding arrangement of
a tool holder and a wire-clamp holder in combination with a control
and evaluation means adapted thereto. An essential characteristic
of the execution of the procedure is that the bonding wire is
firmly gripped and pulled as soon as the bonded connection has been
created (but after the contact between the bonded connection and
the bonding tool has been broken), during simultaneous measurement
of the tensile force.
[0013] In particular, the bonding head or the wire clamp is raised
through a second distance calculated in dependence on the
structural features, in such a way that during the raising process
a predetermined or programmed tensile force is generated and the
intactness of the bonded connection is monitored. The latter is
achieved by observing the time course of the tensile force acting
on the wire clamp during raising. If the bonded connection were to
break while the test force is being applied, the result would be a
sudden decrease in the measured force, and even slighter anomalies
in the time course of the measured tensile force can indicate
deficiencies in the quality of the bonded connection and--as the
result of an appropriate evaluation--provide a reason to modify the
process parameters.
[0014] A testing arrangement suitable for implementing the proposed
solution comprises, as an essential element, the wire-clamp holder
(which is known per se) provided with an associated force-measuring
element and a control device to control the movement pattern
sketched out above, and represents an integrated component of an
improved wire bonder.
[0015] In advantageous embodiments of this testing arrangement, the
wire-clamp holder is seated on the bonding head in such a way that
it can be elastically rotated or linearly displaced against the
action of a pretensioning element. A force-measuring element, in
particular a strain gauge, is associated with the holder, which
also comprises a weakened section in which the tensile force
delivered by the drive mechanism causes an elastic deformation
(bending, twisting or stretching) of the holder. In particular, the
force-measuring element (specifically, the strain gauge) is also
disposed there, so as to obtain a force-measurement signal that can
be unambiguously evaluated.
[0016] So that the testing arrangement can be sensibly integrated
into a modern wire bonding machine, the above-mentioned control
device is designed as a program control system and permits the
testing program to be automatically executed at all or selected
bonded connections that are created with the wire bonder.
[0017] Other advantages and useful features of the invention will
be apparent from the subordinate claims and from the following
description of a preferred exemplary embodiment with reference to
the figure. This shows, in a schematic drawing, a testing
arrangement 1 with essential components of the bonding head 3 of an
ultrasonic wire bonder constructed in accordance with the
invention. The elementary diagram refers to a bonding head of the
kind described in the patent EP 0 857 535 A1, the structural
details of which are not shown here. In the nature of a synoptic
representation, function blocks are added with evaluation and
control functions and symbols for the essential procedural
steps.
[0018] The bonding head 3 comprises a transducer holder 5, in which
is mounted an extension arm bearing an ultrasound transducer 7 and,
attached thereto, a bonding tool 9 (e.g., of the capillary or wedge
type), and a wire-clamp holder 11, which bears a wire clamp 13 for
the controlled fixation of a bonding wire 15. On a substrate 17 the
bonding head produces, in a manner known per se, a bonded
connection 19, the stability of which is to be tested by means of
the testing arrangement 1.
[0019] The wire-clamp holder 11, in a middle region along its
length, has a leaf-spring section 21 as a preferential bending
section, in which is attached a strain gauge 23 or similar force
sensor that responds to bending deformation.
[0020] A drive mechanism 25 (here shown for simplicity as a single
block) of the bonding head 3 controls the bonding head or, as
separately movable components, the tool holder 5 and the associated
extension arm with the transducer 7 as well as the wire-clamp
holder 11 and the wire clamp 13, not only in order to move them in
the manner known per se to generate the bonded connection 19, but
in addition according to a testing program of the kind described
above, which is stored in a program memory unit 27. As a result, in
particular the following sequence is controlled: a first step S1 in
which the bonding tool 9 is lifted slightly away from the bonded
connection 19 that has been produced, a second step S2 in which the
bonding wire 15 is firmly clamped, a step S3 in which the wire
clamp 13 is raised together with the clamped bonding wire 15, and a
step S4 in which an initial value signalled by the strain gauge 23
during lifting is detected.
[0021] The strain gauge 23 is connected to a tensile-force
evaluation unit 29, and its output signal is there evaluated
according to a pre-specified algorithm--for example, incorporating
a threshold discrimination with respect to a minimal tensile-force
value. On the output side the tensile-force evaluation unit 29 is
connected to a bonding-parameter control unit 31, in which the
result of the evaluation is converted as appropriate into
pre-determined changes of the bonding parameters, to ensure the
quality of the bonded connection 19.
[0022] The embodiment of the invention is not restricted to the
example described above, but is also possible in a large number of
modifications that are within the competence of a person skilled in
the art.
LIST OF REFERENCE NUMERALS
[0023] 1 Testing arrangement
[0024] 3 Bonding head
[0025] 5 Transducer holder
[0026] 7 Transducer
[0027] 9 Bonding tool
[0028] 11 Wire-clamp holder
[0029] 13 Wire clamp
[0030] 15 Bonding wire
[0031] 17 Substrate
[0032] 19 Bonded connection
[0033] 21 Leaf-spring section
[0034] 23 Strain gauge
[0035] 25 Drive mechanism
[0036] 27 Program memory unit
[0037] 29 Tensile-force evaluation unit
[0038] 31 Bonding-parameter control unit
* * * * *