Method of manufacturing tuner chassis

A method of manufacturing a tuner chassis, in which a tuner chassis assembly is entirely dipped in a molten solder bath to effect the plating of the chassis surface with a solder layer, and thereafter the chassis assembly is dipped in an oil bath heated to a temperature higher than the melting temperature of the solder and then raised, whereby the state of solder plating on the chassis surface is improved by making use of the mechanism that oil forms an oil film on the chassis.

BACKGROUND OF THE INVENTION 
The present invention relates to a method of manufacturing tuner chassis 
and, more particularly, to method of manufacturing the chassis for high 
frequency tuners such as UHF tuners. 
The prior-art method of manufacturing high-frequency tuners is as follows. 
Initially, a chassis housing is formed by bending a material stamped from 
a steel plate. Also, shield plates for partitioning the interior of the 
housing into a plurality of cavities are stamped from a steel plate. These 
component parts are assembled to obtain an eventual chassis. The surface 
of this eventual chassis is then electroplated with copper and then with 
tin. In the high-frequency tuner, it is usually desired that the 
individual cavities defined by shield plates be perfectly shielded with 
respect to one another. In order to obtain perfect shielding, it has been 
the practice to braze the abutting portions of the shield plates and 
housing with copper. This is carried out by putting the chassis assembly 
together with copper pieces placed adjacent to the abutting portions into 
a high temperature heating furnace. The heating temperature of the furnace 
is set to about 1,000.degree. C., at which temperature the copper pieces 
are fused to join together the abutting portions. 
In the above prior-art method of manufacture, however, a long processing 
time is required due to the heating process in the high temperature 
heating furnace. In addition, perfect sealing of the abutting protions 
cannot be obtained in practice even with the above brazing process, and 
leakage of high frequencies are prone to occur. Further, since the 
assembly is plated with tin, "wiskers" of tin are liable to result, giving 
rise to an accident of shorting between circuits. 
SUMMARY OF THE INVENTION 
A primary object of the present invention is to provide a method of tuner 
chassis manufacture, with which the manufacturing time required can be 
reduced. 
Another object of the present invention is to provide a method of tuner 
chassis manufacture, with which it is possible to obtain perfect shielding 
of the tuner chassis housing cavities from one another. 
A further object of the present invention is to provide a method of tuner 
chassis manufacture, which eliminates generation of whiskers as mentioned 
above on the chassis surface. 
A still further object of the present invention is to provide a method of 
tuner chassis manufacture, with which the abutting portions of the housing 
and shield plates within the tuner chassis can be reliably sealed. 
To achieve the above objectives, according to the invention, the 
electroplating as in the prior art is not performed, and after the plating 
of an eventual chassis surface with a solder layer by entirely dipping it 
in a molten solder bath, and thereafter dipping it in a heated oil bath 
and then raised, the plating solder is permitted to be uniformly coated on 
the chassis surface and is concentrated to a greater thickness in portions 
of the chassis where the housing and shields are joined together by making 
use of the fact that the oil forms an oil film on the chassis surface. 
The above and other objects, and advantageous features of the present 
invention will become more apparent from the following detailed 
description of the preferred embodiments thereof when taking in 
conjunction with the accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Now, the method of the tuner chassis manufacture according to the invention 
will be described with reference to the accompanying drawings. In the 
first step, a housing 2 of the tuner chassis 1 is formed by bending a 
material stamped from a steel plate, and also shield plates 3 for forming 
a plurality of cavities within the housing 2 are stamped from a steel 
plate (This step is referred to as component processing step A). 
Then, the component parts are dipped in, for instance, trichloroethylene 
for removing any oil attached thereto (This step is referred to as oil 
removing step B). 
After the removal of oil, the shield plates 3 are assembled in the housing 
2 to obtain a tuner chassis assembly as shown in FIG. 4. Although not 
shown in the figure, a plurality of convexes for holding the shield plates 
3 in predetermined positions are formed by means of a press on the inner 
wall of the housing 2 (This step is referred to as chassis assembling step 
C). 
The chassis assembly 1 thus obtained is then coated with solder flux for 
ensuring sufficient plating of solder (This step is referred to as flux 
coating step D). 
Subsequently, the chassis assembly 1 is entirely dipped in a molten solder 
bath and then raised therefrom. In this way, the surface of the chassis 
assembly 1 can be plated with solder to a thickness of 5 to 8 microns. At 
this time, the abutting portions of the shield plates 3 and housing 2 are 
provided solder plating owing to the capillarity of the solder (This step 
is referred to as solder plating step E). The chassis assembly provided 
with the solder plating is then brought into a centrifugal separator for 
processing before the solder is solidified (This step is referred to as 
centrifugal separation step). As shown in FIG. 2, the housing 2 is formed 
with a number of holes 5 for installing terminals and electronic parts in 
an electronic circuit. Thus, with the chassis assembly immediately after 
the solder plating step, solder may fill and close the holes 5. The 
centrifugal separation step is effected for removing any solder filling 
the holes 5. This step is not necessary in case where the chassis assembly 
has no such hole as the holes 5. 
Afterwards, the chassis assembly 1 provided with the solder plating is 
dipped in an oil bath heated to such an extent that the solder is fused, 
and is then raised from the bath. Where the solder, with which the chassis 
assembly 1 is plated, is fused at a temperature of, for instance, 
240.degree. C., the oil in the oil bath is heated at least to 240.degree. 
C. The oil used is preferably palm oil. By raising the chassis assembly 1, 
the heated oil on flat wall surface portions of the housing 2 is pulled 
toward the portions thereof joined to the shield plates 3, so that an oil 
film is formed thereover. As the oil film is formed, the solder in the 
fused state follows the movement of the oil. The central wall surface 
portions of the housing 2 or cavities are plated with solder to smoothly a 
uniform thickness, while in the neighborhood of the portions where the 
housing 2 and shield plates 3 joined together solder is concentrated to a 
greater extent owing to the capillarity of solder to promote the 
reliability of the sealing of the joint portions (This step is referred to 
as oil dipping step F). 
The chassis assembly 1 after the oil dipping step is then left for natural 
cooling or forcibly cooled down. Finally, the chassis assembly 1 is 
subjected to an oil removing step G like the afore-mentioned oil removing 
step B, thus completing a tuner chassis provided with the solder plating.