Jet soldering method and apparatus

Details Jet soldering method and apparatus Jet soldering method and apparatus

1999-06-29

2001-07-10

Ryan, Patrick (Department: 1725)

Metal fusion bonding

Process

With removing or reshaping of filler material or flash after...

C228S001100, C228S019000, C228S021000, C228S037000, C228S110100, C228S111500, C228S208000

Reexamination Certificate

active

06257480

ABSTRACT:

CROSS REFERENCE TO RELATED APPLICATION
This application relates to and incorporates herein by reference Japanese Patent Applications No. 10-191573, No. 10-326608 and 10-357707 filed on Jul. 7, 1998, Nov. 17, 1998 and Dec. 16, 1998, respectively.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a jet or flow soldering method and apparatus for soldering electronic circuit parts onto a printed circuit board.
2. Description of Related Art
In a jet (flow) soldering method, as shown in
FIG. 18
, a printed circuit board (substrate)
5
is transferred by a conveyer
94
to stick solder onto a bottom surface (treatment surface) of the substrate
5
. Specifically, the substrate
5
is transferred over a pre-heater
7
, a primary jet (flow) soldering bath
2
and
20
a secondary jet (flow) soldering bath
3
sequentially at a fixed speed by the conveyer
94
.
Thus, the substrate
5
is heated at above the pre-heater
7
, so that a temperature difference between the top surface and the bottom surface of the substrate
5
, which will occur at the
25
time of soldering, is reduced to prevent warping of the substrate
5
. Then, the solder stick onto the treatment surface of the substrate
5
to solder electronic circuit parts to the treatment surface by transferring the substrate
5
over the primary jet soldering bath
2
with the treatment surface of the substrate
5
being immersed in a primary solder jet
21
, that is, contacted to the primary solder jet
21
. Thereafter, the solder sticking onto the substrate
5
is shaped by transferring the substrate
5
over the secondary jet soldering bath
3
with the treatment surface being immersed in a secondary solder jet
31
.
Here, as shown in
FIG. 19A
, the solder stick onto the treatment surface
51
of the substrate
5
by waving the primary solder jet
21
in the primary jet soldering bath
2
. In a case that space
57
between electrode terminals of electronic circuit parts
59
on the substrate
5
is comparatively large as shown in
FIG. 19A
, the solder is enabled to enter and stick to lands
58
by waving the primary solder jet
21
. However, the magnitude of wave is limited because of its dependency on the viscosity, the surface tension and the like of solder. As a result, in a case that the space
57
between the electronic circuit parts
59
on the substrate
5
is small as shown in
FIG. 19B
, the solder is disabled to enter the space. Thus, defect of imperfect soldering increases, as the substrate
5
is integrated highly recently, that is, as the circuit parts
59
are located more closely.
Further, the temperature distribution in the substrate
5
is likely to become non-uniform because of influence of non-uniformity of temperature in the upper surface (heat radiation surface) of the pre-heater
7
. This causes warping of the substrate
5
, and damage to the electronic circuit parts
59
when heated excessively. The pre-heated temperature varies from substrate to substrate. The pre-heating condition is determined only by the temperature, resulting in an impediment to equalization of the pre-heated temperature among the substrates.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a jet soldering method and apparatus, which enables the solder to enter small space so that imperfect soldering and deformation of solder is reduced.
It is a further object of the present invention to provide a jet soldering method and apparatus, which is capable of stabilizing pre-heating prior to soldering.
According one aspect of the present invention, a transfer condition between a transfer of a substrate over a primary jet soldering bath and a transfer over a secondary jet soldering bath is differentiated from each other. Preferably, the substrate is transferred over the primary jet soldering bath at a high speed and over the secondary jet soldering bath at a low speed. Preferably, an elevation angle of inclination of the substrate in upward and downward directions relative to the substrate transfer direction is set smaller over the primary jet soldering bath than over the secondary jet soldering bath. Preferably, a dipping depth of the solder into the solder jet is set larger in the primary solder jet than in the secondary solder jet. Preferably, a horizontal angle of inclination of the substrate in the horizontal direction relative to the transfer direction is set smaller over the primary jet soldering bath than over the secondary jet soldering bath.
According to another aspect of the present invention, a shielding member is provided around a heat radiation surface of a pre-heater to be higher than the heat radiation surface, a substrate mounted with electronic circuit parts is positioned above the heat radiation surface of the pre-heater, and the substrate is immersed in or contacted to the solder jet after holding the position of the substrate for a predetermined time period. The shield member around the pre-heater restricts the heat radiation surface of the pre-heater from cooling down so that lowering of the surface temperature within the heat radiation surface of the pre-heater is restricted to efficiently heat the substrate to equalize temperature distribution in the substrate. Alternatively, the substrate may be swung above the heat radiation surface of the pre-heater to equalize the temperature distribution in the substrate without using the shield member.


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