Heated tool with non-flat heating surface for avoiding solder-bridging

A heated tool for soldering objects to a plurality of pads which are spaced apart by a selected pitch, comprises a tool member having a heating surface with a plurality of spacer bars thereon, spaced by the pitch between the pads. The spacer bars act to separate one pad from the other to avoid the flow of solder between the pads.

FIELD AND BACKGROUND OF THE INVENTION 
The present invention relates in general to heated tools, and in particular 
to a new and useful heated tool for soldering objects to a plurality of 
pads which are spaced apart by a certain spacing, the heated tool 
including spacer bars for isolating the pads from each other. The heating 
tools may either be moved to the objects to be treated or connected, or 
mounted in a fixed position with the object to be treated or connected 
being brought to the heated tool. 
Thermal energy is either supplied to the objects to be treated or 
connected, by radiant heating from heated surfaces of the tool, or by 
direct thermal contact between the heated tool and the object. A 
controlled force is usually applied against the object by the heated tool. 
An additional thermal conductive material may be used to increase heat 
flow from the heated tool to the object. Flux, for example, may be 
provided for increasing the transfer of heat and for reducing oxidation 
during the thermal process. 
Such tools may supply heat either continuously or during selected time 
periods only. Heat may be applied during heating pulses which may be 
activated or controlled by various external conditions, for example, by 
forcing the heated tool against the object to be heated or connected. 
Various sources of heat are known for heating the heated tool to a variety 
of selected temperatures. Hot gases and/or electric current for example 
may be used for heating specified heat supplying areas or surfaces of the 
tool. 
For the present invention, it is preferable to utilize the flow of 
electrical current through a heated tool for heating the tool. This 
permits controlled pulse-heating featuring fast heating rates as well as 
precise temperature control at various areas of the tool. 
A known generally U-shaped heated tool is disclosed in German Pat. 
reference No. 2,848,519. This heated tool is mounted to holders either 
using screws or by welding. This keeps the heat supplying areas of the 
tool in position and further is used to provide electrical connectors for 
feeding electrical heating current to the tool. Such tools can be 
manufactured using sheet metal designs (see German Pat. Nos. 3,144,048.7, 
3,137,859.5 and 3,137,860.9 to the present inventor). These heated tools 
can also be machined from solid materials. 
When transferring thermal energy to one or more objects using one or more 
heated tools, excess heat and relatively long periods of time are 
sometimes needed, particularly when the objects are made of materials 
having high thermal loads. 
The use of force-controlled thermal contact for transferring thermal energy 
from a tool to a part must also be accurately controlled. For this reason 
force-controlled thermal contact has limited applications. Objects having 
high thermal conductivity, for example objects made of metal oxides, 
require different procedures. Continuous preheating for example may be 
necessary for such applications. A heating tool is simply set at a much 
higher temperature to compensate for thermal loads. This has limitation 
however in that excess heat may be damaging to some materials. 
SUMMARY OF THE INVENTION 
An object of the present invention is to provide a heated tool which can 
join two or more parts together by thermal treatment and which can reduce 
or illiminate solder-bridging of parts or areas which are located close to 
each other. Usually, the parts of electric components which are to be 
joined by solder or similar materials, can be positioned to within only 
certain spacings from each other. Closer spacings cannot be utilized since 
solder may flow between the parts causing undesirable bridging and short 
circuits. This occurs when conventional heated tools having flat heating 
surfaces are utilized. 
Another object of the present invention is to provide spacer bars on the 
heating surface of the heated tool which are shaped to match or compliment 
the spacing between the parts that are to be soldered or otherwise heat 
treated. This prevents the undesirable flow of solder from one part to the 
other during the heating cycle. 
In accordance with the invention, the spacer bars can be formed as one 
piece with the heated tools or can be added on as additional structures 
onto the heating surface of the heated tools. In this way the spacer bars 
can be made of materials having different properties than the material of 
the heating surface. Materials having different thermal properites (such 
as low conductivity) or wetting capabilities can be used. Lower 
temperatures can thus be supplied to areas between the parts that are to 
be soldered, to reduce the flow of heat to these areas. By selecting 
wetting properties, the flow of solder to the areas between the parts can 
also be reduced. 
Spacer bars with special shapes and special thermal properties can thus be 
provided on the heated tool. Higher or lower temperatures can be provided 
across the heated tool and its spacer bars to advantageously and closely 
control the flow of solder. 
The various features of novelty which characterize the invention are 
pointed out with particularity in the claims annexed to and forming a part 
of this disclosure. For a better understanding of the invention, its 
operating advantages and specific objects attained by its uses, reference 
is made to the accompanying drawings and descriptive matter in which the 
preferred embodiments of the invention are illustrated.

DESCRIPTION OF EMBODIMENTS 
Referring to the drawings in particular, the invention embodied in FIG. 1 
comprises a heated tool 1 having a non-flat heating surface la which is 
provided with a plurality of spacer bars 3. Electrical current and 
pressure is supplied to the heating surface la by a pair of connector bars 
2, 2. 
The heated tool is particularly useful for connecting an insulated flat 
cable 4 having a plurality of wire or wire bundles 5 that are spaced from 
each other by an insulated web 6, to connector pads 7 which are spaced 
apart by a pitch 9 on the surface of a substrate or a circuit board 13. 
Each pad 7 is provided with a coating of solder 8 for connecting the wires 
5 to the pads 7. 
As also shown in FIG. 4, a section of cable 4 which is to be connected to 
pads 7 is stripped and rendered free of insulation to expose the wires 5. 
As shown in FIG. 2, to heat treat or solder the pads 7 to the wires 5 tool 
is heated in its heating area, as schematically illustrated by crosses 11 
and brought down under pressure in the direction of arrows 12 onto the 
wires 5. The heating causes the solder to melt. Because of the existence 
of spacer bars on the heating surface, the solder is precluded from 
flowing from one pad to the other. The flowing solder is blocked and 
dammed by the spacer bars as shown at 10. 
FIG. 2 also illustrates that the spacer bars can be differently shaped. 
Spacer bar 3a can, for example, be broader than the space between the pads 
and narrow in the vertical direction so that a solder connection is made 
without contacting the spacer bar 3a with the top surface of the pads. 
Alternatively, the spacer bar 3b can be narrow and deep to engage fully 
between the pads. 
In accordance with the present invention, a pitch 9 of 1.27 mm or less can 
be achieved. This corresponds to an equally small pitch for the wires 5 in 
the cable 4. As noted above, this is achieved without the danger of solder 
bridging between adjacent pads. 
FIG. 3 illustrates an embodiment of the invention where one of the spacer 
bars is provided with a plating or coating of material 16. Material 16 can 
be selected to have certain advantageous properties. For example, a 
material having low thermal conductivity can be selected for decreasing 
the amount of heat transferred to the areas between the pads. 
Alternatively, the material can have a higher thermal conductivity for 
increasing the amount of heat provided between the pads. 
Spacer bar 15 of the long narrow type may also be utilized for almost 
touching the board 13 to physically separate the pads from each other. 
FIG. 3 shows the example of the invention wherein the spacer bars are made 
as one piece with the heated tool. 
The embodiment shown in FIG. 3A includes a spacer bar 31 which is connected 
to an otherwise flat heating surface 1a, for example by welding. Another 
spacer bar 32 can be connected into a slot 14 provided in heating surface 
1a. 
By making the spacer bars 31, 32 as separate units from the rest of the 
heated tool, the materials of the spacer bars can be selected for 
desirable properties such as heat transmission or wetting. Material which 
has low wetting affinity for solder may be desirable to avoid the flow of 
solder between the space between pads. 
FIG. 4 shows a manner of assembling and connecting the cable 4 to a circuit 
board 13 which is provided with holes 19 for receiving the arms of a cable 
clamp 18. 
In operation, cable 4 with areas of wires 5 stripped, is brought down in 
the direction of arrow 211 onto pads 7 which are precoated with solder 8. 
The heated tool 1 is then brought down onto the wires and pads in the 
direction of arrow 212 and supplied with electrical current sufficient to 
melt the solder. Spacer bars 3 prevent flow of solder between pads. 
The heated tool 1 is then removed and the solder solidifies. Clamp 18 is 
then brought down in the direction arrow 213 into holes 19 to firmly clamp 
cable 4 to circuit board 13. 
FIG. 5 shows the assembled connection. 
FIG. 6 shows another embodiment of the invention wherein the heated tool 1 
has a non-flat configuration with areas having different cross sections. A 
lower cross section increases the resistance to electricity and would 
increase the temperature of the heated tool in this area. For example, 
small cross sectioned area 21 can be provided at the spacer bar and can be 
dimensioned to contact the surface of adjacent pads at 23. This helps 
transfer heat directly to the pads thus improving and increase the rate at 
which the solder melts and the connection is made. To help isolate the 
pads from each other, an additional projection 22 may be provided at the 
bottom of the spacer bar 21. 
FIG. 6A shows a version of the invention wherein each of the spacer bars is 
solid and touches adjacent pads at 25. Again, heat is transferred to the 
pads, but less heat is provided since the spacer bars have a greater cross 
section than the remainder of the heated tool. 
While specific embodiments of the invention have been shown and described 
in detail to illustrate the application of the principles of the 
invention, it will be understood that the invention may be embodied 
otherwise without departing from such principles.