Substrate having pins

Details Substrate having pins Substrate having pins

2001-04-06

2003-06-24

Feild, Lynn D. (Department: 2839)

Electricity: conductors and insulators

Conduits, cables or conductors

Preformed panel circuit arrangement

C439S083000

Reexamination Certificate

active

06583366

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a substrate having pins serving as input/output terminals arranged in a standing condition, and more particularly to a substrate having enhanced joining strength between pins and a substrate.
2. Description of Related Art
There is known an upright pin-joined (pin grid array) substrate serving as input/output terminals arranged in a standing condition. An example of such a prior art upright pin-joined substrate is shown in
FIG. 4
, which is a partially enlarged sectional view of an upright pin-joined substrate
201
. The upright pin-joined substrate
201
includes a substrate
203
having a substantially rectangular plate-like shape and a number of pins
221
arranged on the substrate
203
in a standing condition.
The substrate
203
includes a dielectric layer
205
having wiring layers (not shown) formed in the interior and on the surface thereof, and a number of pin pads
209
exposed through a solder resist layer
207
on the side of a main surface
203
A.
The pin
221
includes a substantially cylindrical shaft portion
221
A and an enlarged diameter portion
221
B formed at the lower end of the pin
221
and swelling substantially hemispherically toward the corresponding pin pad
209
. The pin
221
is fixedly joined to the substrate
203
such that the enlarged diameter portion
221
B is fixedly joined to the pin pad
209
by means of solder HA.
The upright pin-joined substrate
201
has the following feature. Since the enlarged diameter portion
221
B of the pin
221
assumes a substantially hemispherical shape, a larger amount of solder HA can reside between the enlarged diameter portion
221
B and the pin pad
209
as compared with, for example, a pin having a flat headed, enlarged diameter portion. Since the enlarged diameter portion
221
B is substantially hemispherical, stress imposed on the pin
221
does not concentrate at a specific point, but tends to be absorbed by the entire joint portion.
Accordingly, as compared with an upright pin-joined substrate using pins each having a flat headed, enlarged diameter portion, the upright pin-joined substrate
201
can provide enhanced joining strength between the pin
221
and the substrate
203
(pin pad
209
).
However, when the amount of solder HA for joining the pin
221
and the pin pad
209
is small, the joining strength between the pin
221
and the pin pad
209
becomes insufficient. As a result, when stress is imposed on the pin
221
, the joint portion may fracture.
Specifically, as shown in
FIG. 4
, when solder HA is joined through fusion to merely a spherical surface
221
BK of the enlarged diameter portion
221
B and is thus constricted, stress imposed on the pin
221
tends to concentrate in the vicinity of the constricted portion of solder HA, potentially causing fracture of solder HA at the constricted portion.
Also, when the amount of solder HA for joining the pin
221
and the pin pad
209
is excessively large, stress imposed on the pin
221
may cause fracture of the joint portion.
Specifically, as illustrated with the dashed line in
FIG. 4
, solder HA spreads, through wetting, over the entire shaft side plane
221
BH of the enlarged diameter portion
221
B up to the shaft portion
221
A in such a manner as to form a large fillet F on the shaft side plane
221
BH.
In this case, when stress is imposed on the pin
221
, the pin
221
is unlikely to deform, because of a large amount of solder HA joined through fusion to the shaft portion
221
A thereof; i.e., the pin
221
is unlikely to absorb the stress. As a result, the stress is imposed directly on the joint portion, potentially causing fracture of the joint portion.
The pin
221
having the substantially hemispherical, enlarged diameter portion
221
B generally has a higher barycenter of the enlarged diameter portion
221
B than does a pin having a flat headed, enlarged diameter portion. As a result, when the amount of solder HA is large, stress imposed on the pin
221
tends to cause fracture of solder HA at the joint portion.
Because of the spherical surface
221
BK, the pin
221
is thicker in the enlarged diameter portion
221
B than is a pin having a flat headed, enlarged diameter portion. Thus, when the large fillet F is formed on the shaft side plane
221
BH, the strength of the joint portion becomes rather weak.
SUMMARY OF THE INVENTION
The present invention provides a substrate having at least one pin comprising a substrate, a pin, and solder. The substrate has a main surface and a substantially plate-like shape and comprises a pin pad exposed on the main surface. The pin comprises a shaft portion and an enlarged diameter portion (a flange) greater in diameter than the shaft portion and formed at one end of the shaft portion. The enlarged diameter portion comprises a shaft side plane located on the same side as the shaft portion, and a spherical surface swelling in opposition to the shaft portion. The solder is adapted to join the pin pad and at least the enlarged diameter portion of the pin. The solder extends from the pin pad beyond the circumferential edge of the shaft side plane of the enlarged diameter portion and spreads on the shaft side plane through wetting in such a manner as not to reach the shaft portion. Alternatively, the solder extends from the pin pad beyond the circumferential edge of the shaft side plane of the enlarged diameter portion and spreads, through wetting, over the entire shaft side plane up to the shaft portion in such a manner as to form a fillet on the shaft side plane with an angle formed between a fillet surface and the shaft side plane not exceeding 50 degrees.
According to the present invention, the solder for joining the pin and the pin pad extends from the pin pad beyond the circumferential edge of the shaft side plane of the enlarged diameter portion and spreads on the shaft side plane through wetting in such a manner as not to reach the shaft portion. Alternatively, the solder for joining the pin and the pin pad extends from the pin pad beyond the circumferential edge of the shaft side plane of the enlarged diameter portion and spreads, through wetting, over the entire shaft side plane up to the shaft portion in such a manner as to form a fillet on the shaft side plane. The fillet is relatively small such that the angle formed between the surface of the fillet and the shaft side plane is not greater than 50 degrees.
When the solder extends beyond the circumferential edge of the shaft side plane onto the shaft side plane through wetting, the solder extending between the pin pad and the shaft side plane of the enlarged diameter portion forms a fillet assuming substantially the form of a truncated cone. Thus, a sufficient amount of solder is present for joining the pin and the pin pad, thereby suppressing fracture of the joint portion that would otherwise result from insufficiency of solder when stress is imposed on the pin.
Even in the case where a solder fillet is formed on the shaft side plane of the enlarged diameter portion, when stress is imposed on the pin, the pin itself is deformed to some extent to thereby absorb the stress, because the fillet is relatively small. Thus, stress imposed on the joint portion is lessened. As a result, the joint portion becomes unlikely to fracture.
The pin having the hemispherical, enlarged diameter portion has a higher barycenter of the enlarged diameter portion than does a pin having a flat headed, enlarged diameter portion, because of the hemispherical profile of the enlarged diameter portion. However, since the fillet is relatively small, even when stress is imposed on the pin, the joint portion becomes unlikely to fracture.
As described above, the upright pin-joined substrate of the present invention exhibits resistance to fracture potentially caused by stress imposed on a pin, to thereby enhance reliability.
The pin is not particularly limited, so long as the pin includes the above-mentioned shaft portion and enlarged diameter portion. The shaft portion and the enlarge

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