U.S. patent application number 13/214728 was filed with the patent office on 2011-12-08 for thermode cleaning method.
This patent application is currently assigned to ATS Automation Tooling Systems Inc.. Invention is credited to Ali ABU-EL-MAGD, Joel Anthony Patrick DUNLOP, Arno Krause, Anthony Spithoff, Walter Strobl, Allison Wilson, Ka Ming (Timber) Yuen.
Application Number | 20110297186 13/214728 |
Document ID | / |
Family ID | 44065794 |
Filed Date | 2011-12-08 |
United States Patent
Application |
20110297186 |
Kind Code |
A1 |
DUNLOP; Joel Anthony Patrick ;
et al. |
December 8, 2011 |
THERMODE CLEANING METHOD
Abstract
A method for cleaning a thermode tip including applying an
energy pulse to the thermode tip. The energy pulse involves raising
the temperature of the thermode tip higher than the working
temperature of the thermode tip. A method for cleaning a thermode
tip may include periodically performing a predetermined number of
soldering cycles at a working temperature; and applying an energy
pulse to the thermode tip.
Inventors: |
DUNLOP; Joel Anthony Patrick;
(Cambridge, CA) ; ABU-EL-MAGD; Ali; (Burlington,
CA) ; Yuen; Ka Ming (Timber); (Ancaster, CA) ;
Wilson; Allison; (Cambridge, CA) ; Spithoff;
Anthony; (Burlington, CA) ; Strobl; Walter;
(Ayr, CA) ; Krause; Arno; (Waterloo, CA) |
Assignee: |
ATS Automation Tooling Systems
Inc.
Cambridge
CA
|
Family ID: |
44065794 |
Appl. No.: |
13/214728 |
Filed: |
August 22, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12954781 |
Nov 26, 2010 |
8016180 |
|
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13214728 |
|
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61264690 |
Nov 26, 2009 |
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Current U.S.
Class: |
134/19 |
Current CPC
Class: |
B08B 7/0071 20130101;
B23K 3/08 20130101; B23K 1/206 20130101 |
Class at
Publication: |
134/19 |
International
Class: |
B08B 7/00 20060101
B08B007/00 |
Claims
1. A method for cleaning a thermode having a thermode tip, the
method comprising: applying an energy pulse to the thermode tip
such that the thermode tip reaches a predetermined temperature
above the working temperature of the thermode tip.
2. The method of claim 1 wherein the thermode tip is held at the
predetermined temperature for a predetermined amount of time.
3. The method of claim 1 wherein the energy pulse is externally
applied.
4. The method of claim 1 wherein the predetermined temperature is
at least greater than 120% of the working temperature.
5. The method of claim 1 wherein the predetermined temperature is
at least greater than 200% of the working temperature.
6. The method of claim 1 wherein the predetermined temperature is
at least greater than 250% of the working temperature.
7. The method of claim 2 wherein the predetermined amount of time
the energy pulse is applied is determined by manufacturing
parameters and a temperature range available given the material of
the thermode tip.
8. The method of claim 1 wherein the predetermined temperature is
determined by manufacturing parameters and a temperature range
available given the material of the thermode tip.
9. A method for cleaning a thermode having a thermode tip, the
method comprising periodically: performing a predetermined number
of soldering cycles at a working temperature; and applying an
energy pulse to the thermode tip such that the thermode tip reaches
a predetermined temperature above the working temperature of the
thermode tip.
10. The method of claim 9 wherein the thermode tip is held at the
predetermined temperature for a predetermined amount of time.
11. The method of claim 9 wherein the predetermined temperature is
at least greater than 120% of the working temperature.
12. The method of claim 9 wherein the predetermined temperature is
at least greater than 200% of the working temperature.
13. The method of claim 10 wherein the predetermined amount of time
the energy pulse is applied is determined by manufacturing
parameters and a temperature range available given the material of
the thermode tip.
14. The method of claim 9 wherein the energy pulse is externally
applied.
15. The method of claim 9 wherein the predetermined temperature is
determined by manufacturing parameters and a temperature range
available given the material of the thermode tip.
Description
RELATED APPLICATIONS
[0001] This patent is a continuation of U.S. patent application
Ser. No. 12/954,781 filed Nov. 26, 2010, which claims priority to
U.S. Provisional Patent Application 61/264,690 filed Nov. 26, 2009,
both of which are hereby incorporated herein by reference.
FIELD
[0002] The present document relates generally to thermode cleaning.
More particularly, the present document relates to a cleaning
method for cleaning thermode soldering tips.
BACKGROUND
[0003] Thermodes are devices used for local application of heat and
pressure, typically in soldering applications known as `Hot-bar
reflow soldering`. Once the thermode is brought into contact with a
desired location, localized heating is produced by direct
resistance heating of the tip of the thermode. The `soldering gun`
is a common example.
[0004] The main advantage of thermode soldering is the very rapid
temperature change (up to 1000.degree. Celsius per second) with
precise control over the temperature while the component parts are
being mechanically held by thermode contact pressure. Also, since
the hottest portion of the thermode is typically in direct contact
with the part bond area, efficient heat transfer occurs and rapid
heating of the item is possible. The bond area is the area(s) of
the part being processed where a reflow soldered bond is desired
between at least two surfaces. Since the tips have little thermal
mass, rapid cooling and solidification of the completed bond is
possible. Forced air cooling can additionally be used to reduce the
time required for the soldering cycle.
[0005] There are several styles of thermodes in common use, which
differ mainly by the shape of the tip and material used. A thermode
typically includes the following elements: [0006] Terminals:
electrical contacts where power is applied. [0007] Mount: means of
mechanically supporting the thermode (possibly the same structure
as supports the terminals). [0008] Shank: means of supporting the
tip and conducting current to it. [0009] Tip: high resistance
section where the majority of heat is developed. [0010] Transition
zone: means of joining the tip to the shank. [0011] Working
surface: the portion of the tip, which comes in contact with the
item to be heated. [0012] Thermocouple: a device for determining
the working temperature, attached to the tip near the working
surface
[0013] Issues may arise when the thermode, especially the thermode
tip, requires cleaning due to a build-up of flux/solder residue and
gradual metallurgical contamination of the working surface
(collectively referred to as residue or debris). Even with the
no-clean flux formulations, which may contain less than 5% solids,
there is still residue build-up over time as the actual burn-off
amount for no-clean fluxes is generally about 50% of the initial
flux weight. Cleaning off the residue may require hours of downtime
of the manufacturing system and reduced service life, which can
cost a company many thousands of dollars of lost revenue over a
year. Current methods may require the thermode soldering tips to be
abrasively scrubbed or chemically cleaned every 150 to 175
soldering cycles.
[0014] Currently, various thermode tip cleaning methods are
employed; although not without their disadvantages. Another common
method for thermode tip cleaning is the use of a sponge soaked in
water or a chemical cleaning solution. An air blast may also be
used to clean the thermode tip. Both the air blast method and wet
sponge method generally do not eliminate the need for mechanical
scrubbing of the thermode, but may somewhat reduce the frequency of
the mechanical scrubbing. Each of these methods typically requires
additional tooling at the soldering site. Thus, there is a need for
a method of cleaning a thermode that overcomes at least some of the
deficiencies of conventional systems and methods.
SUMMARY
[0015] This application relates to a method of cleaning a thermode
that is intended to take less time to complete, require minimal
additional tooling or motion and improve the useful life of the
thermode. This cleaning method is also intended not to reduce the
soldering process reliability or generate additional particulates
that may contaminate the local environment.
[0016] In one aspect, there is provided a method for cleaning
thermode tips including the application of an energy pulse to the
thermode tip while the thermode tip is not in contact with a bond,
such that the thermode tip reaches a predetermined temperature
above a working temperature of the tip. This method may result in a
longer interval between normal mechanical scrubbing cycles and a
substantial increase in thermode life.
[0017] In another aspect, described herein, a method for cleaning a
thermode tip is provided, including, periodically: performing a
predetermined number of soldering cycles at a working temperature;
and applying an energy pulse to the thermode tip while the thermode
tip is not in contract with a bond, such that the thermode tip
reaches a predetermined temperature above a working temperature of
the tip.
[0018] In the above methods, the energy pulse may result in the
thermode tip reaching the predetermined temperature for a
predetermined amount of time.
[0019] In some cases of the above methods, the temperature of the
thermode tip may be raised above the working temperature during the
energy pulse. In some cases, the thermode tip may be raised to a
temperature that is at least greater than 120% of the working
temperature, to at least greater than 200% of the working
temperature, or to at least greater than 250% of the working
temperature. The temperature and the amount of time that the energy
pulse will be applied can be determined based on manufacturing
parameters and the temperature range available given the material
of the thermode tip.
[0020] In some cases of the above methods, the energy pulse is
externally applied.
[0021] Other aspects and features will become apparent to those
ordinarily skilled in the art upon review of the following
description of specific embodiments in conjunction with the
accompanying figures.
BRIEF DESCRIPTION OF DRAWINGS
[0022] Embodiments will now be described, by way of example only,
with reference to the attached Figures, wherein:
[0023] FIG. 1A illustrates the front view construction of a typical
thermode.
[0024] FIG. 1B illustrates the side view of the typical thermode in
FIG. 1A.
[0025] FIG. 1C illustrates the perspective view of the typical
thermode in FIG. 1A.
[0026] FIG. 2 illustrates a flow chart of a typical thermode reflow
soldering process.
[0027] FIG. 3 illustrates a flow chart of a typical thermode
cleaning cycle as practiced in the current state of the art.
[0028] FIG. 4 illustrates a flow chart of a thermode cleaning
method according to one embodiment of the present application.
[0029] FIG. 5 illustrates a thermode working surface after 175
bonds since the last performed mechanical scrubbing, using the
typical cleaning cycle as practiced in the current state of the
art.
[0030] FIG. 6 illustrates a thermode working surface contamination
after 375 bonds since the last performed mechanical scrubbing using
the cleaning method provided for in the present application.
[0031] FIG. 7A illustrates reflow soldering temperature profile
without using the present method.
[0032] FIG. 7B illustrates reflow soldering temperature profile
according to one embodiment of the energy pulse cleaning
system.
DETAILED DESCRIPTION
[0033] In one aspect herein, a method for cleaning a thermode tip
comprising applying an energy pulse to the thermode tips is
disclosed
[0034] A typical thermode construction is illustrated in FIG. 1.
The thermode includes terminals (1) where the power is applied and
a shank (2) for supporting and conducting current to a tip (3). A
transition zone (4) allows for the joining of the tip (3) to the
shank (2). The working surface (5) is the portion of the tip, which
comes in contact with the part bond area. The tip (3) and, in
particular, the working surface (5) generally require cleaning due
to residue build-up, a by-product of running soldering cycles.
[0035] FIG. 2 illustrates a typical thermode reflow soldering
process. The thermode is first lowered to the bond area (10). The
thermode is then ramped up to a preheat temperature (11) to the
required temperature level for the bond. Once the preheat
temperature is achieved the thermode holds at this temperature
(12). The application of the thermode to the bond raises the bond
above the liquidus temperature (13). The thermode is then cooled,
which cools the bond below the solidus temperature (14). The
cooling may be facilitated by an air blow off. The thermode tip is
then moved off the bond area (15). There will generally be a move
to the next bond location (16) or a part may be moved under the
thermode location to expose a new bond location. This thermode
soldering process is typically under 6 seconds per bond. In some
cases there may be a wait (17) prior to moving to a new bond area
or a new part being ready to be soldered and the process
restarting.
[0036] FIG. 3 shows a flow chart of a typical cleaning cycle.
First, the thermode solders a current bond area (20), for example,
as shown in FIG. 2. Once the current bond area is soldered the
process must determine if the part itself is complete (21). If
there is at least one other bond area on the current part the
process will generally move to the next bond (22), until all bonds
on the part are complete.
[0037] If all the bonds on the part are completed the bond quality
may be checked (23), for example by electrical testing or the like.
If the bond quality is acceptable, the method will wait for the
next part (24) then restart the cycle. If the bond quality is
determined to be inadequate, a mechanical scrubbing (25) of the
thermode tip may need to be performed. It will be understood that,
in some cases, the bond quality may actually be checked while, in
other cases or alternatively, a predetermined number of bonds may
be set as the limit for when the mechanical scrubbing will be
performed. The predetermined number may be determined in advance by
conducting testing or studies of the bonds produced.
[0038] The mechanical scrubbing (25) may take upwards of 20 seconds
to perform before the thermode may come back online and continue
with the soldering process. After the mechanical scrubbing is
performed, the quality of the thermode may be checked to determine
if the thermode is worn out (26) or if it is able to continue with
the next soldering cycle. The checking of the thermode may be a
visual check, a test of heating capability, or other type of test
as known in the art. If the thermode is worn out, production may be
stopped for maintenance (27) during which the thermode is replaced.
Stopping the production and completing the maintenance may take
significant time, sometimes upwards of half an hour. During this
time the soldering process is halted. Throughout a year, this
downtime may add up to thousands of dollars of lost revenue.
[0039] Mechanical scrubbing (25) includes manually scrubbing the
thermode with an abrasive material like a scrubbing pad or
sandpaper. In this process, both the residue and a portion of the
tip material are typically removed. This process may later
compromise the mechanical structure of the thermode, reduce the
thermal mass, and alter the electrical resistivity of the heat
generating path. All of these may wear out the thermode and
compromise the effectiveness of the soldering process and reduce
the thermode life. Frequent mechanical scrubbing will increase the
overall process time, taking minutes to move the scrubbing tool
into position and perform each scrubbing cycle.
[0040] Other physical cleaning techniques may also be applied
either in addition to or instead of completing mechanical scrubbing
each time the bond quality is found to inadequate. For example, wet
sponge method may be used. However, this method requires a sensor
to determine the wetness of the sponge to be used to clean the
thermode tip. Further, this cleaning method must be completed when
the thermode tip is hot, which may become a fire hazard. As with
mechanical scrubbing, the wet sponge cleaning may be required every
cycle and may necessitate additional tooling including a motor for
moving the sponge, a water container and pump to keep the sponge
wet.
[0041] An air blast may also be used to clean the thermode tip
although this method has the possibility of generating airborne
particulate that could contaminate parts and the local environment.
With use of either the wet sponge method or air blast method,
mechanical scrubbing may still be required if the bond quality is
found to be inadequate after the wet sponge or air blast cleaning
have been completed.
[0042] In order to overcome at least some of the drawbacks of
conventional methods, the present application provides a method of
applying an energy pulse to the thermode tip either after each
soldering operation, after each part, after a predetermined number
of soldering operations, or the like. As shown in FIG. 4, the
soldering process of the present method commences similarly to a
conventional method, in that a current bond is soldered (30), the
process determines if the part is complete (31) and if there is at
least one other bond area on the current part, the process will
move to the next bond (32).
[0043] Once a part is complete, the bond quality may be reviewed
(33) and, if the bond quality is adequate, the method will perform
an energy pulse cleaning (34). This energy pulse cleaning (34) may
preferably be performed during idle time when the thermode is
otherwise not being used, for example, waiting for a new part to
enter the process.
[0044] The energy pulse consists of an elevation of the thermode
tip temperature to a predetermined temperature higher than the
working temperature of the thermode for a predetermined period of
time. In this way, the energy pulse may be considered to be a
function of time and temperature and the amount of energy to be
input, whether through high temperature for a short time or a lower
temperature for a longer time. The temperature and time can be
determined based on various factors or through testing as will be
understood in the art. In a manufacturing environment, the time
available is typically controlled by process parameters such as
part movement, number of actions performed, and the like. As such,
the temperature needed is generally at least partly predetermined
by the amount of time available. It will, of course, be understood
that, in some cases, it may be necessary to raise the temperature
of the thermode tip for a time longer than the cycle time
available, however this is generally not preferred with regard to
manufacturing efficiency.
[0045] In a conventional soldering process, the thermode tip
temperature is typically lowered below the working temperature when
the thermode is idle (see FIG. 7A, described in further detail
below). This may be, for example, because energy can be conserved
by allowing the thermode tip to cool when idle. In contrast to this
conventional approach, the method herein raises the temperature of
the thermode tip above the working temperature using the energy
pulse. Generally, it is preferred if the increase of the
temperature is to a temperature that is at least greater than 120%
of the working temperature. In some cases, the temperature may be
greater than 150% of the working temperature. In other cases, the
temperature may be greater than 200% of the working temperature. In
still other cases, the temperature may be greater than 250% of the
working temperature. In all cases, the increase in temperature
should be kept below any temperature that may damage the thermode
tip. As noted above, the time available for the energy pulse is
often determined based on other factors but may be in a range
greater than 0.1 sec in accordance with the temperature to be used.
It will be understood that the word "pulse" as used herein is not
intended to limit the amount of time that the energy may be applied
but is used for convenience because the time is ideally shorter
than longer in terms of manufacturing efficiency.
[0046] The energy pulse is generally performed when the thermode
tip is out of contact with the bond area so that additional heating
of the bond area does not occur. The temperature may be raised by
normal operation of the thermode and using closed loop temperature
control. Alternatively, the temperature may be elevated by exposing
the tip to an external source of energy or heat; although this
approach may require additional tooling.
[0047] In one particular example the flux used is a tin based flux
that may have a liquidus temperature of 240.degree.. Normal reflow
temperatures for soldering with this material may have a working
temperature of 320.degree.. In this example, the energy pulse is
configured to raise the temperature of the thermode tip to
approximately twice the working temperature for a period of
approximately 10 seconds, which, in this process, was the amount of
time needed to ready the system to solder the next part.
[0048] During energy pulse cleaning (34), it is believed that any
solder remaining on the thermode tip is raised to a temperature
sufficient for the surface tension of the solder to form spherical
beads on the working surface and at least a portion of the residue
is burned off the tip and vaporized. It may be that with, for
example, the use of a titanium thermode, the residue does not bond
well to the titanium oxide that is typically present on the
thermode tip and the energy pulse allows the titanium oxide to
reform and protect the thermode tip. Other chemical reactions may
also be occurring that protect the thermode tip from residue.
[0049] Small amounts of combustion by-products may be created
during the energy pulse process. In some cases, the remaining
solder and combustion by-products may stay on the thermode tip and,
during the following soldering cycles, it is believed that the
debris is transferred back from the thermode tip to the surface of
the solder joint as the solder is melted. The debris appears to
remain on the surface and it is believed that the debris is not
transferred into the bond.
[0050] Once the energy pulse cleaning is completed the system is
ready to process the next part (35) and begin this cycle again. If
at the end of the next or subsequent cycles the thermode tip
cleanliness is inadequate (33), mechanical scrubbing may be
performed (36). After the mechanical scrubbing the quality of the
thermode tip may be reviewed (37) and if the thermode needs to be
replaced the production may be stopped for maintenance (38).
[0051] The cleanliness of the thermode tip may be estimated or
determined in a variety of ways, which will assist with determining
the number of solder operations (cycles) between energy pulses and
mechanical cleanings. For example, the energy transfer to the bond
from the thermode tip may be monitored, either during test runs or
in production, to determine an appropriate number of soldering
cycles before cleaning.
[0052] Tests have shown that the energy pulse cleaning method
significantly reduces the need for mechanical scrubbing cycles. In
one example, it was found that mechanical scrubbing was required 4
times more often on thermodes not exposed to the energy pulse.
Also, thermodes that were exposed to the energy pulse cleaning were
capable of almost 3 times as many bonds before wearing out and
needing to be replaced.
[0053] The increased cleanliness of the thermode using the method
herein is further illustrated in FIGS. 5 and 6. FIG. 5 illustrates
a thermode working surface after 175 bonds since the last performed
mechanical scrubbing using the typical state of the art while FIG.
6 illustrates the working surface contamination after 375 bonds
since the last performed mechanical scrubbing using the energy
pulse cleaning method. Even with over twice as many bonds, the
thermode making use of the energy pulse cleaning method contains
less residue than the working surface of the thermode in a typical
process.
[0054] FIGS. 7A and 7B illustrate the soldering temperature
profiles with and without using the energy pulse cleaning method.
In FIG. 7A, the process begins with an idle temperature (40)
followed by a ramp up (41) then a short holding of the temperature
(42) prior to the soldering commencing (43). Once the soldering is
completed the traditional process cools down (44) then waits at an
idle temperature (46) prior to repeating the above process. In FIG.
7B, the temperature profile for the present energy pulse cleaning
method commences in a similar manner in that the thermode starts at
an idle temperature (40), heats up (41) then holds at that
temperature (42) prior to starting the soldering process (43). The
present method then provides for an energy pulse (45) after the
thermode has completed the bonding process (44). It is this energy
pulse that aids in the cleaning of the thermode and reduces the
residue thus reducing the frequency for mechanical cleaning. As
noted above, the energy pulse is not necessarily applied after each
soldering operation. Further, the thermode tip may not necessarily
need to be cooled prior to applying the energy pulse.
[0055] This energy pulse cleaning method allows for the energy
pulse cleaning to be accomplished without additional external
tooling. As the carbon debris and excess solder may remain on the
thermode tip and be removed in a later soldering cycle, no debris
is expelled into the air, no wet sponge cleaning or the like is
required and no additional mechanical wear and tear is experienced
by the thermode tip during the energy pulse. The mechanical
scrubbing of the thermode tip is required at a reduced frequency in
the present method, which may extend service life of the thermodes
tips.
[0056] The energy pulse method is intended to create a continuous
self-cleaning mechanism, which may keep the thermode tip generally
clean and free of debris. It has been observed that applying this
method to titanium thermodes, the titanium thermodes stayed
reasonably clean even after over 700 soldering cycles. No further
scrubbing was required to dress the thermode tip for further
soldering process during these cycles.
[0057] This method is preferably used in conjunction with titanium
thermodes tips; although, thermode tips made of molybdenum,
Inconel.RTM., tungsten and other metals having similar properties
may also benefit from this process. Presently preferred thermode
metals include: low resistance grades of titanium such as
commercially pure Ti in ASTM grades 1, 2, 3 or 4; alloys of Ti with
moderate resistivity such as ASTM grades 12, 15, 17 or 9; other
alloys of titanium particularly for thermodes with relatively small
tips. The use of this method with non-titanium thermodes has not
been tested in detail.
[0058] In the preceding description, for purposes of explanation,
numerous details are set forth in order to provide a thorough
understanding of the embodiments. However, it will be apparent to
one skilled in the art that these specific details may not be
required in order to practice the embodiments. In other instances,
well-known electrical structures and circuits may be shown in block
diagram form in order not to obscure the embodiments.
[0059] The above-described embodiments are intended to be examples
only. Alterations, modifications and variations can be effected to
the particular embodiments by those of skill in the art without
departing from the scope, which is defined solely by the claims
appended hereto.
* * * * *