Method of forming a blind solder joint in an ignition coil

A method of forming a solder joint between a cup shaped high voltage terminal and a secondary lead extending from a secondary coil within a plastic case of an ignition coil. The steps include securing a solder paste to an inwardly extending end of the high voltage terminal, positioning the secondary coil lead relative to the solder paste, and heating the joint without making physical contact therewith to promote melting of the solder to secure and electrically connect the desired components.

TECHNICAL FIELD 
The present invention concerns a method of forming a solder joint at a 
position within an assembly that is not directly accessible for the 
application of heat. More specifically, the present invention is directed 
to a method of soldering two components within a plastic housing without 
physically contacting either component. 
BACKGROUND OF THE INVENTION 
Ignition coils as are suitable for use with internal combustion engines act 
to provide a high voltage level electrical current which may be supplied 
to a spark plug. The current supplied is at a sufficient potential to 
create an arc across the spark plug gap to ignite the gasoline in the 
cylinder to power a piston of the internal combustion engine. In order to 
create this high voltage power source, a primary coil and a secondary coil 
are positioned relative to each other such that high voltage is generated 
in the secondary coil. 
A particular type of ignition coil has a plastic housing which defines a 
high voltage opening in which a cup shaped high voltage terminal is 
secured. The housing additionally includes a main opening in which the 
primary and secondary coils are secured and wherein they are encapsulated 
within an epoxy material to pot the entire structure. With such a 
structure, however, it is necessary to make an electrical connection 
between an extending lead from the secondary coil and the high voltage 
terminal. This solder connection is made within the interior of the 
housing and is in effect a blind joint. 
The previous method of performing this solder joint included melting a bead 
of solder of significant size and allowing this bead to become affixed to 
the inwardly extending end of the high voltage terminal and then inserting 
the terminal into the terminal opening in the housing. The secondary coil 
was then positioned in the main opening with secondary lead contacting the 
solder bead. The operator would manually hold the secondary coil in 
position while a heated rod is inserted into the center of the cup shaped 
high voltage terminal to make physical contact therewith. The heated rod 
would act to re-melt the bead of solder on the terminal and by holding the 
secondary coil in position relative to the melted solder and against any 
force applied by the heated rod, a solder joint could be formed. 
However, in the above described method it is necessary to position the 
ignition coil in the desired orientation, to insert the heated rod into 
the high voltage terminal and to simultaneously manipulate the secondary 
coil to be aligned with the solder bead and to maintain the secondary lead 
in contact with the solder bead as physical force is applied within the 
high voltage terminal by the heated rod. Although effective, this method 
requires several manual steps, a skilled operator and, of necessity, must 
use a relatively large solder bead. 
The hereinafter described method accomplishes soldering using noncontact 
soldering methods and solder paste. In such a manner, the quantity of 
soldering material utilized as well as the number of steps necessary to 
perform the soldering operation are reduced. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide a method for forming a 
blind solder joint between a high voltage terminal and the lead of the 
secondary coil within a plastic housing of an ignition coil. 
It is a yet further object of the present invention to provide an improved 
method for forming a blind solder joint using a reduced amount of solder 
material. 
It is another object of the present invention to provide an improved 
assembly method wherein the secondary coil need not be manually positioned 
during the soldering operation. 
It is a further object of the present invention to provide means for making 
a blind solder joint wherein heat is directed to a specific location to 
form the solder joint without damaging plastic members in which the 
components to be soldered are secured. 
It is another object of the present invention to provide a safe, 
economical, reliable, and easy to duplicate method of assembling an 
ignition coil using a blind solder joint. 
Other objects will be apparent from the description to follow and the 
appended claims. 
The above objects are achieved according to a preferred embodiment of the 
invention by the method of forming a solder joint between a cup shaped 
high voltage terminal to be inserted within a high voltage opening in a 
plastic case of an ignition coil and a projecting secondary lead extending 
from a secondary coil inserted within a main opening in the case. The 
steps of the method include securing solder paste to the inwardly 
extending end of the high voltage terminal, positioning the high voltage 
terminal within the high voltage opening in the case of the ignition coil 
with the inwardly extending end projecting to the main opening in the 
case. The secondary coil is then placed in the main opening of the housing 
with the secondary lead positioned to contact the solder paste secured to 
the high voltage terminal. The last step is heating the inwardly extending 
end of the high voltage terminal, the secondary lead and the solder paste 
to melt the solder paste to form a solder joint therebetween, said heating 
being accomplished without applying physical pressure to the high voltage 
terminal. Heating may be accomplished by using infrared radiation, radio 
frequency radiation, or focused streams of hot air among other methods. 
Also disclosed is a process for electrically connecting the inwardly 
extending end of a cup shaped high voltage terminal secured within a case 
to a projecting lead from a secondary coil also secured within the case, 
said case having a main opening extending in a first direction in which 
the secondary coil is secured and a high voltage terminal opening 
projecting in an opposite direction in which the high voltage terminal is 
secured, said projecting lead and said high voltage terminal being 
positioned adjacent each other within the interior of the case. The steps 
of the process include affixing a low melting temperature solder paste to 
the inwardly extending end of the high voltage terminal, positioning the 
high voltage terminal within the high voltage terminal opening with the 
inwardly extending end positioned to be electrically engaged by a 
secondary lead to be positioned within the case, placing the secondary 
coil within the main opening of the case with the secondary lead 
positioned adjacent the inwardly extending end of the high voltage 
terminal and melting the solder paste to form a solder joint between the 
secondary lead and the high voltage terminal by using noncontact heating 
means.

PREFERRED EMBODIMENT OF THE INVENTION 
The invention herein will be described with reference to making a blind 
solder joint within a specific ignition coil structure. It is to be 
understood that other types of blind solder joints and similar 
applications could likewise use the techniques presented herein. 
Reference will be made herein to a low melting temperature solder paste. 
This solder paste is a commercially available material made by Alpha 
Metals, Inc., 600 Rte. 440, Jersey City, N.J. 07304, and Kester Solder 
Company, Division of Litton Industries, 4201 Wrightwood Avenue, Chicago, 
Ill. 60639, typically having a melting temperature in the range of 
270.degree. to 300.degree. F. and being sufficiently sticky or having 
sufficient adherent qualities that it directly adheres to the high voltage 
terminal and to the secondary lead of the secondary coil when positioned 
adjacent thereto. The case as described hereafter is made of a plastic 
material typically having a melting temperature of 350.degree. to 
400.degree. F. Hence, by the use of the solder having a sufficiently lower 
melting temperature, it is possible to make the solder joint without 
affecting the structural integrity of the plastic case. A typical solder 
paste having a higher melting temperature may also be suitable. 
Referring first to FIG. 1, there may be seen ignition coil 10 having 
bracket 12 to which coil core 20 is mounted. Bolts 13 help secure coil 
core 20 to bracket 12 and then may be utilized for mounting the ignition 
coil to the desired end use. Coil core 20 extends within the central 
opening of primary coil 14 which is located within the central opening of 
secondary coil 16. Secondary coil 16 includes a secondary bobbin 18 and 
secondary lead plate 44. Plastic case 30 is shown extending around the 
primary coil, the secondary coil, and a portion of the coil core and 
defines main opening 31 in which the primary and secondary coils are 
positioned. The main opening in addition to the primary and secondary 
coils and the coil core is filled with epoxy 36 to encapsulate these 
components within the opening. 
Case 30 additionally includes a portion which extends to define a high 
voltage opening 32 which is generally cylindrical in configuration. High 
voltage terminal 40 is secured within high voltage opening 32 and has an 
inward end projecting to be positioned relative to secondary lead plate 44 
of the secondary coil. It is between these two elements where the solder 
joint is formed. Terminals 34 for supplying power to the primary and 
secondary coils are additionally shown. 
FIG. 2 shows high voltage terminal 40 being generally cylindrical in 
configuration and having rib 41 which coacts with a mating indentation 
formed in the high voltage opening of the case to secure the high voltage 
terminal in position. The inwardly extending end of high voltage terminal 
40 is labeled abutment portion 42 and includes an indentation portion 45 
in which solder paste 43 is placed. As previously indicated, the solder 
paste has adherent qualities and maintains itself within the indentation 
portion. 
FIGS. 3 and 4 show side and end views of secondary coil 16. Secondary coil 
16 is formed by winding an elongated electrical conductor about secondary 
bobbin 18 in myriad of turns such that the desired voltage level is 
generated in the secondary coil. The secondary windings which are formed 
from this continuous conductor are labeled secondary windings 19 and 
include a connecting winding 46 connecting the turns of the winding to 
secondary lead plate 44. Of course, it is not necessary to actually have a 
separate secondary lead plate and the connecting winding may be directly 
soldered to the high voltage terminal. As may be seen in FIG. 4, secondary 
bobbin 18 is generally rectangular in configuration and has a central 
opening 15 into which the primary coil may be positioned. Additionally, 
secondary lead plate 44 is shown extending upwardly for easy soldering 
with the high voltage terminal. 
FIG. 5 shows an end view of the ignition coil of FIG. 1. The pyramidal 
configuration of case 30 is shown relative to the positionings of 
secondary coil 16 and primary coil 14. Coil core 20 is shown having a 
portion extending within both coils. Terminals 34 are also shown. 
High voltage terminal 40 is shown towards the top of case 30 in the 
pyramidal portion and specifically abutment portion 42 extending into the 
main opening of the case is shown. Solder paste 43 secured at the end of 
the abutment opening is shown as is secondary lead plate 44 extending 
upwardly from the secondary coil to contact the high voltage terminal and 
the solder paste. 
Additionally shown in FIG. 5 on the right-hand side is an infrared lamp 50 
and lens 52. It is shown schematically to indicate the infrared heat 
energy supplied by lamp 50 may be focused by lens 52 to be concentrated on 
the area to be soldered to effect melting of the solder to secure the 
secondary lead plate to the high voltage terminal to provide a good 
electrical connection without providing sufficient heat energy to melt the 
case, the bobbin, or the other plastic components of the ignition coil. 
On the left-hand side of the ignition coil as shown in FIG. 5 is a source 
of radio frequency energy. This RF source 60 is likewise positioned such 
that when it is energized, appropriate radio frequency radiation is 
focused at the solder joint. Additionally, a stream of hot air (not shown) 
could be focused in the same area on the exterior case or within the high 
voltage terminal to create the same effect. 
In order to effect the solder joint as described herein, the high voltage 
terminal has an abutment portion and has an indentation portion formed 
therein. The solder paste in a very small amount is provided in this 
indentation portion. The secondary coil is inserted within the main 
opening of the case with the secondary lead plate extending to engage the 
solder paste. The structural dimensioning of the components located within 
the main opening help to secure the secondary coil in position. The slight 
adherence of the solder paste against the secondary lead additionally 
helps to secure the ignition coil in the desired postion. This minor bit 
of adherence in conjunction with the application of heat energy without 
physically contacting the solder joint, is sufficient to allow the solder 
to be melted and a good electrically conductive solder joint to be formed 
without the further necessity of requiring manual positioning of the 
secondary coil during the solder operation. As previously described, an 
external source of heat energy may be focused infrared radiation, focused 
radio frequency radiation, a hot air stream or the like. 
The invention has been described with reference to a particular embodiment. 
It is to be understood by those skilled in the art that variations and 
modifications can be effected within the spirit and scope of the invention 
.