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BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a
lead frame used for connection of internal elements of an electroacoustic transducer such as a
sounder, speaker, microphone, earphone, pickup, magnetic head, etc. and connection with an
external element. It is.
2. Description of the Related Art For example, in the case of a sounder which is a type of
electroacoustic transducer, the lead frame 1 is a molded body formed by etching or punching a
metal substrate as shown in an example of FIG. The lead terminals 6A, 6B, 6C, 6D are inner lead
portions, and a base member formed by synthetic resin is integrally formed with a base member
including a pole piece portion (not shown) on the inner lead portion as shown by imaginary lines
in FIG. After molding and connecting the end of the coil installed on the pole piece on the base
portion to a lead terminal, a synthetic resin case for forming a resonance chamber is joined to the
base portion to cover and electrically Package the acoustic transducer and bend the outer leads
7A, 7B, 7C, 7D of the lead terminals by 90 ° to form external connection terminals. Electroacoustic transducer is completed form. In the figure, reference numeral 5 denotes a guide hole
for processing the lead frame and forming it on the lead frame 1. The external connection
terminal is an important part to be soldered to the surface mounting substrate.
Recently, Cu-Zn-based (for example, Cu-30% Zn, Cu-40% Zn) and Cu-Sn-based (for example, Cu4%) have been used as lead frames (hereinafter referred to as "frames") of such electroacoustic
transducers. Alloys such as Sn-0.2% P) (hereinafter abbreviated as "substrate") have come to be
used. As the frame material of the above-described Cu-Zn-based and Cu-Sn-based alloy, one
having an elongation percentage of 5 to 50% has been used in order to prevent the occurrence of
cracks during bending. More specifically, for example, a plate of Cu-30% Zn-based alloy is
subjected to Cu undercoating of 1 μm thickness and then a bright solder plating of 5 to 7 μm
thickness is applied thereon as a frame. ing. The gloss plating is employed to improve the
solderability of the substrate. Also, for example, a Cu-4% Sn-0.2% P alloy subjected to Ni
undercoating with a thickness of 2 to 5 μm and then subjected to bright solder plating with a
thickness of 5 to 7 μm is also used as a frame. ing.
[Problems to be solved by the invention] When resin sealing is performed using a frame
subjected to such plating, and the outer lead portion is subjected to 90 ° bending in the final
step, the bending corner portion of the metal substrate is obtained. Fine cracks are generated,
and further, when soldering on a substrate, these fine cracks cause deterioration of solder
wettability due to time-dependent change in a bent portion, and a soldering failure in substrate
mounting occurs.
In addition, when a Cu-Zn-based alloy is used for the frame, Zn precipitates and diffuses to the
solder plating layer at the time of soldering, thereby significantly inhibiting solder wettability.
Similarly, when the outer lead portion of a Cu-Sn alloy plated frame with solder gloss plating is
bent at 90 °, even if micro cracks do not occur in the base, micro cracks occur in the solder
plating layer, When bonding the outer lead to the lead of the external element at the time of
board mounting, a soldering failure occurs.
Such a soldering failure in substrate mounting is a serious problem in terms of the reliability of
the electroacoustic transducer. That is, when the cause of failure of the electroacoustic
transducer was analyzed, it was found that there was a connection defect because solder at the
time of mounting did not flow into the cracked part, which is one of the causes.
SUMMARY OF THE INVENTION In view of the above, as a result of various studies, the present
invention develops a lead frame for an electroacoustic transducer capable of manufacturing a
highly reliable electroacoustic transducer while performing economical plating on the frame. In a
frame molded from a metal substrate strip having an elongation of 20% or more, the entire
surface or at least the lead terminal portion of the frame is Ni-plated with a plating solution
containing no brightening agent, and the brightening agent is applied thereon It is characterized
in that solder plating is performed using a plating solution which does not contain it.
In the present invention, each plating is performed without containing a brightening agent
consisting of an organic compound such as thiourea, saccharin or glucose, or an inorganic
compound such as thiosulfate in the Ni plating bath and the solder plating bath.
This is because when the brightening agent is contained, the plating surface becomes bright and
the plating structure becomes finer, and when the frame is bent, cracks easily occur in the plating
film. The plating formed by the plating solution not containing the brightening agent is
hereinafter referred to as "matte plating".
As the nickel plating solution, a normal bath, a watt bath, a semi-bright bath, a sulfamic acid bath
and the like can be used, but a watt bath is particularly preferable. Similarly, as a solder plating
bath, a hydrofluoric acid solder plating bath, a methanesulfonic acid bath or the like can be used,
but a methanesulfonic acid bath is preferable.
Furthermore, in the present invention, to set the elongation percentage of the metal substrate
strip alloy to 20% or more, the metal base having an elongation percentage of less than 20% is
subjected to press forming or plating after etching and then to bending processing. This is
because a crack is generated at a corner of the lead portion, and the base plating is oxidized by
the time-dependent change, and the wettability of the solder is deteriorated.
That is, according to the present invention, a metal substrate sheet alloy having an elongation
percentage of 20% or more is formed into a frame by pressing or etching and then, as shown in
FIG. Is provided with a matte Ni undercoat of 0.05 to less than 0.3 μm, and a coating of a matte
solder plating of 1 to 10 μm, preferably 5 to 7 μm thick thereon.
Ni and solder plating may be applied to the entire surface of the frame, or at least applied to the
lead terminals, and may be plated and coated to a desired thickness by electroplating. In
particular, 90% Sn-10% Pb-based solder is preferable as the solder.
Fe-Ni system such as Fe-35.5 to 36.5% Ni alloy, Fe-40.5 to 41.5% Ni, Fe-49.5 to 51.5% Ni alloy as
metal base in the present invention Alloys and copper alloys such as brass, phosphor bronze,
phosphor bronze for springs, etc. are preferably selected, but if the elongation percentage is 20%
or more and the familiarity of Ni base plating is good and the solder wettability is good, Other
metal substrates can be selected.
In order to set the elongation percentage of the Fe-Ni alloy to 20% or more, a step of setting the
rolling ratio (plate thickness reduction ratio) of temper rolling after recrystallization annealing to
10% or less may be employed.
In addition, although the elongation percentage is further increased when strain relief annealing
is performed after temper rolling, strain relief annealing at 500 to 600 ° C. is preferable in
order to prevent a decrease in strength. Also, after rolling, an elongation percentage of 20% or
more can be obtained by performing temper annealing at 600 to 700 ° C. However, temper
rolling has less variation in quality than temper annealing.
For copper alloys, rolling ratio of temper rolling of recrystallization annealing is 20% or less for
brass, 15% or less for general phosphor bronze, and 25% or less for spring phosphor bronze. And
an elongation rate of 20% or more can be obtained.
The frame of the present invention is configured as described above, and by setting the
elongation of the metal base to 20% or more, the occurrence of cracks at the time of 90 °
bending of the lead terminal portion is prevented.
Furthermore, by covering the surface of the lead terminal portion mounted on the substrate with
Ni plating, the diffusion of the component element from the base material is prevented. Also, by
making the Ni plating and the solder plating coated on the base material be matte plating, the
occurrence of micro cracks in the plated portion due to 90 ° bending is prevented.
Therefore, the thickness of the matte Ni plating needs to be 0.01 to 2 μm, and if the coating
thickness is less than 0.01 μm, the alloying elements contained in the metal substrate under the
heating conditions at the time of plastic sealing and The effect of the impurity element as a
diffusion barrier is lost, and if it exceeds 2 μm, a larger effect can not be obtained, which is
uneconomical. The thickness of the Ni coating layer is preferably 0.05 to 0.3 μm.
As in the conventional method, when bright Ni plating is applied, the electrodeposited nickel
becomes a lot of strain and microcrystals and as a result, it is harder and less processable than a
metal substrate, so cracks occur when bending the outer lead portion of the lead terminal. In the
electro-acoustic transducer, the radius (r) is 0.5 mm or less, and the ratio (r / t) to the plate
thickness (t) is 2.5 or less. Strictly, since excellent processability is required for the plating layer,
matte Ni plating is used in the present invention.
The thickness of the solder covering layer is preferably 1 to 10 μm. If the covering thickness is
less than 1 μm, the soldering strength at the time of substrate mounting is insufficient, and if it
exceeds 10 μm, the solder becomes excessive and uneconomical is there.
The thickness of the solder covering layer is preferably 5 to 7 μm. Also, the reason why the
solder covering layer is made matte plating is the same reason as in the case of Ni plating.
Hereinafter, the present invention will be described in detail by way of examples.
Preferred as the matte plating bath composition and conditions of the present invention are as
follows. A. Matte Ni plating bath composition Nickel sulfate: 200 g / L to 250 g / L Nickel
chloride: 35 g / L to 45 g / L Boric acid: 20 g / L to 30 g / L pH: 4 to 5 bath temperature: 40 °
C. to 55 ° C. current Density: 1A / dm2 to 8A / dm2B. Matte solder plating bath composition
stannous borofluoride: 80 g / L to 120 g / L lead: 20 g / L to 40 g / L free hydrofluoric acid: 80 g
/ L to 120 g / L free boric acid: 20 g / L to 30 g / LB naphthol: 0.5 g / L to 3 g / L formalin: 8 g /
L to 15 g / L pH: 4 to 5 bath temperature: 15 ° C. to 30 ° C. current density: 1 A / dm 2 to 6 A
/ dm 2
[Examples] Fe-36% Ni alloy, Fe-42% Ni alloy, Fe-50 Ni% alloy, 0.2 mm thick, each having an
elongation of 20%, and brass, phosphor bronze, as specified in JIS H 3110 For the phosphor
bronze for spring specified in JIS H 3130, the metal base strip is a strip-like test piece of width
10 mm and length 100 mm in the rolling direction, and these are described as Examples 1 to 6 of
the present invention. Tested and evaluated.
Matte Ni plating was performed by the following method.
Nickel sulfate 240 g / L Nickel chloride 45 g / L Boric acid 30 g / L pH 5.0 (2) Bath temperature
50 ° C. (3) Current density 5 A / dm 2
Matte solder plating was performed by the following method. Stannous borofluoride 80 g / L
lead boro fluoride 10 g / L free hydrofluoric acid 100 g / L free boric acid 25 g / L β-naphthol 1
g / L formalin 20 g / L pH 5.0 (2) bath temperature 25 ° C. 3) Current density 3A / dm2
Also, as a comparative example, a metal base of the same type as above having an elongation rate
of less than 20% is used as a comparative example, and a strip-shaped test piece of 0.2 mm in
thickness, 10 mm in width and 100 mm in length is adjusted as described above, evaluation test
Provided for.
The bright Ni plating was performed by the following method.
Nickel sulfate 300 g / L Nickel chloride 50 g / L Boric acid 40 g / L Brightener (saccharin) 1.5 g /
L pH 4.5 (2) Bath temperature 50 ° C (3) Current density 5 A / dm2
The bright solder plating was performed by the following method. 1. stannous borofluoride 150
g / L lead borofluoride 50 g / L free hydrofluoric acid 100 g / L free boric acid 25 g / L βnaphthol 1 g / L formalin 20 g / L brightener (amine aldehyde system) 60 g / L pH 5. 0 (2) Bath
temperature 25 ° C (3) Current density 3A / dm2
The alloy composition of the substrate is as follows. Fe-36% Ni alloy: 36.1% Ni, 0.3% Mn, 0.1% Si,
0.003% C, balance FeFe-42% Ni alloy: 41.6% Ni, 0.5% Mn , 0.3% Si, 0.004% C, balance FeFe-50%
Ni alloy: 49.8% Ni, 0.6% Mn, 0.4% Si, 0.003% C, balance Fe phosphor bronze ( 1): 3.8% Sn, 0.18%
P, balance Cu phosphor bronze (2): 4.8% Sn, 0.20% P, balance Cu phosphor bronze (3): 6.1% Sn, 0
.19% P, balance Cu phosphor bronze (4): 7.9% Sn, 0.21% P, balance Cu 70/30 brass (1): 30.5%
Zn, balance Cu 70/30 brass (2): 35 .8% Zn, balance Cu 70/30 brass (3): 37.5% Zn, balance Cu
spring phosphor bronze: 7.9% Sn, 0.20% P, balance Cu
The following evaluation tests assuming plating and substrate mounting were performed using
the above test pieces. (1) Plating adhesion: After subjecting a metal substrate to a prescribed base
plating and 90% Sn-10% Pb solder plating, it is subjected to 90 ° bending (inner radius 0.2 mm)
in a direction parallel to rolling, The presence or absence was observed.
(2) Solderability of plating: 60% Sn-40% Pb solder in which a test piece obtained by applying a
rosin-alcohol flux to a test piece obtained by subjecting a metal substrate to a predetermined
base plating and solder plating is maintained at 230 ° C. For 5 seconds, and the solder wet area
was observed.
(3) Solderability after heat resistance test: A test piece obtained by subjecting a metal substrate to
a predetermined base plating and solder plating is subjected to 90 ° bending in a rolling parallel
direction and then heated in the air at 150 ° C. for 24 hours Soldering was performed by the
method of the previous section (2).
The test results of each are shown in Tables 1 and 2.
Moreover, evaluation of each characteristic was performed by the following method. Adhesion of
plating: The test piece was bent at 90 ° to determine the presence or absence of plating peeling.
Solderability of plating: 95% or more of solder wet area passed, and less than 95% was rejected.
Solderability after heat resistance test: A solder wet area of 95% or more was passed, and less
than 95% was rejected.
As is apparent from Tables 1 and 2, Invention Example No. 1 to 6 are comparative examples no.
Compared to 7 to 12, it can be seen that the mounting state has high reliability. Moreover,
comparative example No. Even when using a phosphor bronze for spring having an elongation
rate of 20% or more as in No. 12, corner cracks are observed in the plating layer in the 90 °
bending test in the case where the shiny base Ni plating is applied. It is clear that the failure rate
is high and the reliability is poor.
As described above, according to the frame of the present invention, it is possible to effectively
exhibit the high elongation rate of the metal base and the characteristics of the solder plating,
and to manufacture a highly reliable electroacoustic transducer. It is. This frame is also expected
to require a high elongation of metal substrate and solder plating, and to bring about a
remarkable effect as a frame of electronic parts subjected to severe bending.
Brief description of the drawings
1 is a chart (Table 1) showing the structure and characteristics of the lead of the embodiment of
the present invention.
2 is a chart (Table 2) showing the structure and characteristics of the lead of the comparative
3 is a cross-sectional view showing the frame of the present invention.
4 is a plan view of the press-molded frame of the present invention.
Explanation of sign
1 Frame 2 Metal base 3 Matte Ni plating coating layer 4 Matte solder plating coating layer 5
Guide hole 6 Lead terminal 7 Outer lead part of lead terminal (external terminal)