Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
1:L673Z7
HOT AIR REWOR~ TOOL
BACKGROUND OF THE INVENTION
The present invention relates to apparatus and a
method for soldering/desoldering circuit components from a
pc assembly. While the hot air rework tool (HART) has
general applicability to any soldering/desoldering situation,
its great~s~ dvantage to date has been in "field rewolk"
situations requiring the removal/installation of individual
components (i.e., DIP's flatpacks, SSI, MSI and LSI inte-
grated circuits) from a multilayer pc assembly at a customersite. For situations having multilayer pc assemblies of
relatively few layers and/or components with relatively few
pins, standard direct contact, resistance heating techniques
can be used; but as the number of layers and pin counts in-
crease so does khe difficulty of the removal/installationoperation. Primarily troublesome is the attandant heat
sinking or spreading effect of the pc assembly, which efiect
requires higher heats. ~lhe higher heats in turn can damage
the pc assembly by causing "measling" or delamination of th~
layers and/or the components.
While many devices exist that facilitate the
soldering/desoldering operation, from wave soldering to
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~1673~7
direct contact heat transfer devices, some of which further
have suction means for removing molten solder and extractor
means for holding a component and facilitating its removal
or insertion, none of these devices have proven to be cost
effective or amenable to the "field rework" situation, es-
pecially for relatively thick multilayer pc assemblies~
Prior to the development of the HART, components were gen-
erally removed using soldering irons and vacuum solder "gob-
blers. Il The process was relatively tedious though and re-
quired a variety of attachments to accomodate the varioussize packages and pin configurations encountered on the high
density, ~ultilayer pc assemblies.
The HART and method described herein however uses
hot air as the primary heat transfer media and is adjustable
to accomodate various size pc assemblies and components. The
HART can heat either or both of the localizéd upper and lower
surfaces of the pc assembly in the proximity of the desired
component in either a concentrated or diffused manner, there-
by creating a more uniform heat exchange environment which
overcomes the heat spreading effects of the pc assembly. The
HART also does away with the necessity of a solder suction
device in that the air flow can more uniforml~v maintain the
temperature of the solder in all the vias associated with a
component so that all the pins can be inserted or removed
without encountering any cold vias, which vias will not permit
the component pin to be inserted or removed.
116~32~
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The present soldering/desoldering method is
further improved by the application of a heat sensitive
lacquer to the component or localized area during the
solder/desoldering operation, which lacquer will melt at
a specific temperature and thus indicate that the component
can be removed or a new component inserted.
SUMMARY OF INVENTION
In accordance with an aspect of the invention
there is provided a soldering apparatus using hot air as a
primary heat transfer media which controllably localizes
the area of heating upon a workpiece, said soldering
apparatus comprising plenum means for confining and
directing alr flow; blower means attached to said plenum
means for producing said air flow~ heater means within
~aid plenum means for heating said air flow in said plenum
means to a temperature sufficient to cause solder to melt;
~electable size orifice means occluding the hot air flow
output end of said plenum means for selectably
concentrating the hot air flow to a selectably sized
localized substrate area upon said workpiece; and means
for ~upporting a workpiece substrate with respect to said
orifice mean~ end of ~aid plenum means such that said hot
air flow thereof impinges either a component or components
soldered to said workpiece substrate, or a localized area
of ~aid workpiece substrate where a component or
components is to be added or a portion of a component
which is itself solderably fabricated and also soldered to
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said workpiece substrate, whereby a soldered component or
components can respectively be removed from said workpiece
substrate, or a new component or components can be added
thereto said workpiece substrate, or a solderabl~
fabricated component may be disassembled or assembled
while soldered thereupon said workpiece substrate: whereby
said controllably localized area of heating upon said
workpiece via said selectable size orifice means occluding
sald hot air flow is thusly at size of plural components,
a component or a portion of a component; whereby selective
soldered components can be selectably desoldered from said
workpiece substrate or selective new components soldered
thereto.
~RIEF DESCRIPTION OF THE DRAWINGS
Flg. 1 i8 a side view of the hot air rework tool
with a lower air plenum shown in a partlal cutaway section.
Fig. 2 is a schematic diagram of the electrical
wiring of the hot air rework tool.
Fig. 3 is a flow chart of the typical sequence of
events that occur during a replacement operation.
B
1~673Z7
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DESCRIPTION OF THE PREFERRED RMBODIMENT
Referring to Fig. 1 the hot air rework tool (HART)
is shown in a partially sectioned side view and wilI now be
described with particular reference to its primary components.
The method of use will then be described with reference to
the flow chart of Fig. 3 and the typical se~uence of steps
that are recommended for the use of the HART. The HART is
essentially comprised of a primary air plenum 1 to which are
attached a retractable upper air plenum 2, a lower air plenum
3, a support ~rid 4, a blower ~, a h~.se plate 6, an ori~ice
indicator 7 and a pin straightener 8. The HART further is of
a size such that with its appurtenant parts the entire unit
can be placed within an attache case. The size and weight of
the HART thus accommodates the typical field rework circum-
lS stances in which it finds its primary use. Referring nowto the primary components each will be described in detail
with respect to its appurtenant part~; and the roles th.ey play
in the operation of the HART.
The primary plenum 1 essentially consists of a
rectangular air cavity to which the blower 5 i5 attached and
within which the control wiring ~not shown) is affixed. It
functions to distribute the air that is forced into it under
a positive pressure via blower 5 into the upper plenum 2 and
lower plenum 3. The primary plenum 1 is in turn attached to
%5 the base plate 6 which has four rubber cushioned legs 9 at-
tached to it to prevent the HART from sliding on or marring
1~673Z~
a work surface upon which the HART is placed.
The blower 5 is positioned approximately midway
bet~een the upper plenum 2 and the lower plenum 3 such that
the blown air is distributea evenly into the upper and lower
air plenums 2 and 3. The air upon entering the upper and
lower air plenums 2 and 3 passes over respective upper and
lower resistance heatin~ elements 10 (only one of which is
shown but both of which typically are identical in size and
heat rating) which are affixed to the primary plenum 1 wîthin
the cent,ex of the upper' and lower air plenums 2 and 3. The
air is then heated via heaters 10 to a temperature of approxi-
mately 600 to ~0 Farenheit. Due to the positive pres-
sure of the blower 5,,the a.ir is then forced to pass across
the blades of the brass turbulators 11 ~only the lower
plenum's turbulator.s are shown) which are mounted within thé
upper and lower plenums 2 and 3'to cause a turbulent rather
than a swirl.in~ or straight line air flow. A turbulent flow
is preferred since a swirl.ing or straight line flow can cause
hot spots upon the exiting of the heated air from the orifices
12 of the upper and lower plenums 2 and 3, It should,be
noted that the blad~s o.f the turbulators 11 are positioned
such that the pitches of the blades are contra to one another
so that the turbulent flow rather than the swirling flow is
created. It should also be noted that the turbulators 11
are constructed from brass and are secured to the upper and
lower air plenums 2 and 3 via brass bolts 13 and thus act
to also collect any static electricity that may be present
1~67~Z7
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in the heated air and conduct the static electricity to the
chassis ground.
Upon reference to the cutaway sections of the
lower air plenum 3, its associated turbulators 11 and heater
10 can be seen in their relative positions within the lower
air plenum 3, but it is to be recognized that they are also
similarly positioned within the upper air plenum 2. The
upper and lower air plenums 2 and 3 are each also made from
plated steel tubing and are coated on their interior sur-
fa-es with a refracfory ceramic cement 1~. The ceramic 14
acts to electrically insulate the metallic walls of the
upper and lower air plenums 2 and 3 from the possible short-
circuiting of the heaters 10 and also acts to partially in-
~ulate the metallic plenums 2 and 3 from the 600 to 650
Farenheit operating température to which the air is heated.
It i5 also to be noted that additionaL ceramic 14 is placed
at the outside 90 bend within the air plenums 2 and 3 to
assist in directing the heated, turbulent air toward the
orifices 12. The hot turbulent air is then forced out of
the upper and lower orifices 12 and directed onto the spe-
cific location or component on the pc assembly that is posi-
tioned between the upper and lower orifices 12,
The size opening in the orifices 12 is adjusted
to the size of the circuit component or location of the pc
assembly that is to be heated. In most applications, however,
the size of the lower orifice 12 is usually selected to be
;~673Z7
--8--
larger than the component or area to be heated so as to
diffuse the heat it generates over a larger area and thuS
crea-te a relatively high ambient temperature at the com-
ponent site, while the upper orifice 12 is selected to con-
centrate the heate~ air only to the circuit comp~nent orlocation, The upper and lower orifices 12 can be replaced
via the thumbscrews 15 which serve to affix the orifices 12
to the air plenums 2 and 3. The HA~T can ~hus a~comodate
varying sized circuit components and the varying packaging
arrangements ~i.e. pl~stlc or ceramic) that are used in
high ana '.ow densit~ pc ~ssemblies.
Re.~erring now t~ the upper plen~ 2~ it too is
connected to the prim~r~ plenum 1 by a connector assembly
16,.but where the lower plenum 3 was directly connectea by
connector 16~ the upper plenum 2 is connected via an upper
slee~e 17 that i~ in tu.rn con.nected to the primary plenu~ 1
by its connector 16 and which sleeve 1'7 has eith~r one or
two retractor slots 18 f~rmed there.in on opposite sides
thereo~ (only one o~ which is shown)~ such that the upper
plenum 2 can slide forward ar~d backward within the sleeve 17.
The forward travel of the upper plenum 2 being restricted
by the stop screws 18a (only one of which is shown) and the
reverse travel restricted by the inside back wall of the
primary plenum 1. The travel of the upper plenum 2 is con-
trolled by the kno~ 19 attached to the upper plenum 2 and
which is formed from a heat insulating material SO that the
operator .is not burned while extending or retracting the
upper plenum 2. It is to be noted that in the fully retracted
11~7327
g
position when the upper plenum 2 abuts the inside back wall
of the primary plenum 1, the notch 20, let into the side of
the upper plenum 2, acts to permit only a restricted air
flow t~ pass through the upper plenum 2. This condition,
however, will be described ~ore fully he~einafter with ref-
erence to Fig. 2 and the control circuitry.
Positioned i~nedlately above the upper plenum 2 is
the orifice indicator 7 which is shown in a partially raised
and fully lowered position and which is used to indicate the
center of the lower orifice 12'when a pc assembly is placed
on the support grid 4, since thé'lower orifice 12 will be
hidden in this situation. The'indlcator 7 is hin~ed by hinge
21 at the approximate center of the'indicator.7 and enables
the indicato.r 7 to.be raised during the solder/desolder oper-
ation and lowered when a new comp~nent or location is beiny'selected, Thus during the'typical select.ion process, it is
necessary for the operator to place'the upper plenum 2 in its
fully retra~ted position which enables the orifice indicator
7 to be l~wered so as to align itself with the center of the
lower orifice 12 and which then a.llows the'operator to select
a specific component or location on the'sur~ace of the pc as-
sembly and be assured that the center of the'lower orifice 12
is immediately beneath the tip of the indicator 7, The indi-
cator 7 is then ra.ised and the upper plenum 2 extended into
its most forward position so that the center o the oriices
12 are immediately above and below one another.
~L6~32~
--10--
Also contained on the orifice indicator 7 is a
ground spring 22 which is attached such that spring pressure
is exerted against the upper air plenum 2 so as to make elec-
trical contact with and ground any elec-trical charge which
may collect on the upper plenum 2. The spring 2.7 is neces-
sary in the case of the upper plenum 2 since the connector
16 essent;ally connects the sleeve 17 and not the upper
plenum 2 itself to the primary plenum 1. Thus a positive
chassis ground is insured for both the upper plenum 2 and
upper sleeve 17 to the primary plenum 1.
ALso attached to the primary plenum 1 is the sup-
port yrid ~ which essentially provides a padded support sur-
face for the pc assembly between the upper and lower orifices
1~, The support gr.id ~ in the preerred embodiment is com-
pr.ised of four intersecting rails of appropriate lengths toaccommodate the various sizes of the typical pc assemblies
encountered in the field operations and facilitate the rework
of components which are positionea not only in the center of
the pc assemblies but also on the edges. It should be noted
20 that the rails of the support grid 4 are each covered with
a nylon insulator 23 which ensures that the pc assembly is
not d~maged during rework. It should also be noted that the
area circumscribed about the lower orifice 12 by the inter-
secting rails of the support gri.d 4 should be sufficiently
large so that the air which is deflected from the lower sur-
face of a pc assembly does not cause the support grid 4 to
become unduly hot, but yet sufficiently large so as to ac-
1 ~6 7 3 2 7
commodate the smallest pc assembly tha~ will be encountered.
Additlonally, a pin straightener 8 is attached tothe top of the primary plenum 1 which has a variety of com-
ponent pin con~i~urations let into it so as to enable the
operator to plu~ inaividual circuit components into it prior
to inse~tion in the pc assembly and thereby straighten ana
realign all the pins o~ the circuit component. Such a
straightening operation becomes very critical when the pin
c~unt per package is high, such as in the ca~e ~ 64 or 128
pln package. In th~se c~ses the misaligmnent o~ one or
more pins can make it ~ery ~i~icult to insert the component
into a new location or a replacement location.
Referring now to Pig. 2 the control circuitry for
the HART will be described, The ~ART operates ~rom a 120
~olt, ~inyle phase AC supply which is fused on its positi~e
side by fuse Fl which is contained in fuseholder 24. The
power is then controlled by the double-pole/three po3ition
switch swl which supplies the power to the windings of -the
blower motor Ml and the respe~tive upper and lower heaters
10. ~he switch SWl is a three position switch havin~ an
"off~" "cold~" and "hot" position. The "cold" position cor-
responds to only the blower 5 (i.e. motor Ml) operating and
the "hot" position corresponas to the blower 5 and the upper
and lower heaters 10 operating. A diode Dl ~not shown in
Fig, 1) is also provided to partially rectify the AC power
that is supplied to the heaters 10.
~6~3Z7
-12~
Also includea is a single pole~single throw limit
switch sw2 (not shown in Fig. 1) which is wired in series
between dio2e Dl and the upper heater 10. The switch SW2 is
positioned within the primary plenum 1 such that anytime the
upper plenum 2 is partially retracted, the plenum 2 engages
the actuator assembly o~ the switch sw2 causing its contacts
to open and disconnect the power to the upper heater lO. Thus
when the upper plenum 2 is retracted, only cool air is blown
through the upper plenum 2. It should be recalled that when
the upper plenum 2 is fully retracted the air ~low is also
substantially ~estricted ~y the no~ch 20. Thus in the full~
retracted poSition~ the restricted air flow in the upper
plenum 2 acts to minimize the likelihood of the operator
being burned, should he touch the upper plenum 2 as he posi
tions the pc assembly~ and to prevent the inaavertent heating
of undesired components. It should also be recognized ~ecause
the lower heater 10 is directly coupled between the switch SWl,
the lower hea~er 10 will always be "on" so long as the switch
SWl is in the "hotl' position. Consequently the lower plenum
3 Will continUe to provide hot air while the pc assembly is re-
positioned, unlegs Switch SWl is switched to itS "cold" or
"off" position or unless an additional switch is placed in
series with the lower heater 10.
The method employed in usiny the H~RT Wlll now be
described with reference to the flow chart of Fig. 3 and the
typical sequence of events that occur during a normal component
replacement operation. Prior to using the HARrr, it is ini-
~673Z7
-13-
tially preheated by placing the switch SWl in the "hot"
position while the upper plenum 2 is fully extended for
approximately three to f~ur min-~tes. And while waiting for
the HART to heat up to its operating temperature, the oper-
ator prepares the replacement components, as necessary, byusing the pin straightener ~ to straighten and align the pins
of the replacement components; applying a suitable solder
flux to the pins, if needed to insure a good solder connec-
tion; loading the insertion tool with the desired replacement
component to facilitate the insertion of the replacement com-
ponent; and,/or coat.ing the components to be removed with a
temperature sensiti.ve lacquer.
Upon preheating, the switch SWl is then switched
to itB "off" position and the upper plenum 2 is retracted.
The operator can then center the desired component over the
lower orifice 12 with the aid of the orifice .indicator 7.
After positioning the desired component over the lower orifice
12, the movable portion of the orifice indicator 7 is then
folded up and out o the way; the upper plenum 2 is extended
so that the upper orifice 12 is centered immediately above
the desired component; and the switch SWl is switched to the
"hot" position which causes the upper and lower heaters 10
to turn on and again heat the air flow that is again being
forced by the blower ~ through the upper and lower plenums
2 and 3.
1~67327
During the removal or insertion step the HART
thus subjects the component to a heat of approximately 600
to 650 Farenheit with the upper plenum's heat being con-
centrated on the component while the lower plenum's heat is
spread over a slightly larger area. In this manner the am-
bient temperature around the selected component is raised,
while the heat on the upper surface o the component is con-
centrated ana transferrea by the component's package to the
individual pins, since the package and pins are relatively
good heat conductors, especially in ceramic packages. The
l~calized hea~ing of the component's ~ins thus causes the
solder surrounding each of the pins in their associated vias
to melt so that removal can ~e accomplished.
It is to be recognized, however, that while the
use of the HART is bei'ng described' in a process ~or removiny
entire components, it can also be used to remove portions of
components, such as in those cases where'the components are
fabricated using bump soldering or hybrid techniques, In
thèse cases though the hea't Erom the upper plenum 2 is crit-
ical and is used to heat the integrated circuit die, not the
pins~ while the component's cover is removed. For the typi-
cal component though, the internal connections are made using
lead bonding techniques, which require a heat of llO0 to
1~00 ~arenheit, and thus the internal connections are unaf-
25 fected by the HAR~'s 600 to 650 Farenheit temperatures.
1~673'~7
-15-
The above removal process is further facilitated
by the use of the previously mentioned heat sensi~ive lac-
quer, which typically comprises a 4~0 Farenheit mpilaq~
(manufactured by the Tempil Corporation) and which typically
S is applied to the upper surface of the component. Thus upon
the localized heating of the lacquer and the component with
the HART, the lacquer will melt when it reaches its 400
Farenheit melting point which indicates the relative temper-
ature of the solder in the vias of the pc assembly and which
minimizes the duration of exposure and amount of heat applied
to the component. ~Ipon the melting of the lacquer, the op-
erator should then rock the component slightly to determine
that the solder surrounding all of the pins has melted suf-
ficiently, and upon this assurance or with slightly more
heating time, the operator can remove the component. It
should be noted that the typical removal operation accordingto the above described process takes two to three minutes
but that more may be required for large components.
During the rernoval of the old component, the upper
plenurn 2 is fully retracted; but subsequent to removal, it
is then generally returned to its fully extended position
so as to maintain the temperature of the solder in the vias
where the new component will be inserted. When the operator
is ready to insert the new replacement component, the upper
2S plenum 2 is aga.in retracted and the component is inserted
into the vias. If the solder is not sufficiently pliable,
the component can be placed above the vias and the upper
1~6~73'~7
-16-
plenum 2 again extended so as to heat the component and re-
heat the vias, and upon reheating, the component should all
into place, if all the pins are properly aligned. Additional
solder and flux can also be added at this time as necessary.
After replacement of a component, the switch SWl
is switchea to the "cool" or "o~f" position and the pc as-
sembly either removed or repositioned but only a~ter the
operator is sure that the solder connections have solidified.
The above ~escribed operation is then repeated for
10 each of the identified components until all rework is com-
pleted. Upon completion, the upper plenum ~ iS returned toits fully extended position an~ switch SWl is turned to its
"cool" position to allow the upper and lower plenums 2 an
to cool, During this time the pc assembly can then be
15 cleaned to remove flux or okher ContaminantS which might ad-
here to it rom the rework process.
While the ~IART and its method of op~ration have
been described With re~erenCe to the preferred embodiment~it is to be recognized that the individual companents oE the
design can be changed in any number of manners without de-
parting from the spirit and scope of the claims hereinafter
set forth. Some possible changes might be to include a
clamping means to the base plate 6 whereby the HART can be
clamped to a work table if space allows. One may also desire
to use different variations of the heaters 10 such as a
1~673Z7
-17-
larger element so as to provide a different heating rate.
One may desire to make both the upper and lower plenums 2 and
3 retractable so as to accomodate greater size variation~ in
pc assemblies and also make the HART easier to package and
carry. One might further desire to change the knob 19 to
provide a pulley arrangement for retracting and extending
the upper plenum ~ so as to minimize the likelihood of the
operator contacting the heated upper plenum 2. One may
still further desire to vary the control wiring to accomodate
different circumstances. But, it is to be recognized that
e~ch of these aforementioned variations are mere variat.ions
o the described invention and they should not detract from
the spirit and scope of the claimed invention.
What is claimed is:
