Abstrict A method of making a moisture-proof package that holds semiconductor
devices and desiccant is provided. A tray that retains desiccant
is prepared. Semiconductor devices are placed on the tray, and the
semiconductor devices and the desiccant carried by the tray are
then heat treated before being sealed in a moisture-proof bag. Once
the semiconductor devices are shipped to customers, the tray and
desiccant are both reused until the moisture absorbing properties
of the desiccant diminish.
Claims What is claimed is:
1. A method of making a package, comprising: preparing a tray that
retains a desiccant; providing one or more semiconductor devices
on the tray; heating the tray; and sealing the tray in a moisture-proof
container.
2. The method according to claim 1 wherein the tray and the desiccant
retained therein are recovered after use.
3. A method of reusing a desiccant, comprising: recovering a tray
in which a desiccant is retained; providing one or more semiconductor
devices on the tray; heating the tray; and sealing the tray in a
moisture-proof container.
4. A tray for containing semiconductor devices, comprising: a plurality
of pockets for accommodating one or more semiconductor devices having
individual packages; and a retainer that retains a desiccant, wherein
the tray sustains enough heat to substantially remove any moisture
absorbed by the individual packages.
5. The tray according to claim 4 wherein the retainer includes
a groove in which the desiccant is placed, and a cover to retain
the desiccant in the groove.
Description BACKGROUND OF THE INVENTION
[0001] 1. Field of Invention
[0002] The present invention relates to a method of making a package
containing semiconductor devices and desiccant.
[0003] 2. Description of Related Art
[0004] Semiconductor devices, which are individually packaged,
are subjected to electrical testing and lead inspection. The devices
are then heat-treated at, for example, 125.degree. C. for 16 to
24 hours to remove moisture that may be absorbed by the individual
package before being shipped, for instance, to customers. Such heat-treatment
is necessary at least when the individual package is a plastic package,
because plastic material is susceptible to absorb moisture from
the air. Removing the moisture allows to prevent separation and/or
cracking of the individual package which may result from the rapid
expansion of water inside the individual package during mounting
of the semiconductor devices onto print-circuit boards.
[0005] Although moisture can be removed from the individual package
by heat treatment before, for instance, shipping, moisture may be
re-absorbed by the individual package during the course of transportation
of the semiconductor devices.
[0006] To overcome this problem, magazines, trays, or tapes containing
the individually packaged semiconductor devices are sealed in a
moisture-proof container (e.g., a bag made of a film having a low
moisture permeability). In addition, desiccant is put into the container
together with the semiconductor devices thereby to make a moisture-proof
package containing semiconductor devices and desiccant. The desiccant
is included in the package so that, if the moisture-proof package
is stored for a long period of time, or if the hermetic seal of
the moisture-proof bag is defective, the elements present inside
the moisture-proof package are kept moisture-free. Such a moisture-proof
package containing semiconductor devices and desiccant is described
in U.S. Pat. No. 4971196 which is incorporated by reference in
its entirety.
[0007] According to this conventional method, the desiccant, which
is assumed to be effective in keeping the elements inside the moisture-proof
package moisture-free, is prepared separately from the semiconductor
devices. When the desiccant is left in a humid environment for a
long period of time prior to being incorporated in the package with,
for instance, semiconductor devices, however, it loses some of its
moisture absorbing properties. As a result, it becomes difficult
to ensure that the elements inside, i.e., the semiconductor devices,
are kept moisture-free.
[0008] In other words, additional care must be taken in order to
keep the desiccant in a dry environment before it is put into the
moisture-proof package, in order to ensure a moisture-free environment
inside the package.
[0009] Moreover, in this conventional method, the desiccant is
discarded after a single use, thereby increasing the burden for
proper waste control because large quantities of desiccant are discarded.
SUMMARY OF THE INVENTION
[0010] An object of this invention is to provide a method of making
a package, for instance, containing semiconductor devices, that
ensures a moisture-free environment inside the package, without
any necessity for additional care in the preparation of the desiccant.
Another object of this invention is to reduce the burden of waste
control due to frequent discard of desiccant.
[0011] To achieve such objects, an exemplary embodiment according
to this invention provides a method of making a package, which includes
preparing a tray that retains a desiccant, placing semiconductor
devices on the tray, heating the tray, and sealing the tray in a
moisture-proof package.
[0012] An exemplary embodiment according to this invention also
provides a method of reusing a desiccant, which includes recovering
a tray in which a desiccant is retained, providing semiconductor
devices on the tray, heating the tray, and sealing the tray in a
moisture-proof container.
[0013] Another exemplary embodiment according to this invention
provides a tray for containing semiconductor devices and which includes
a plurality of pockets for accommodating one or more semiconductor
devices having individual packages, and a retainer that retains
a desiccant wherein the tray sustains enough heat to substantially
remove any moisture absorbed by the individual packages.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] Various exemplary embodiments of the methods of this invention
will be described in detail, with reference to the following figures,
wherein:
[0015] FIG. 1 is an illustration of an exemplary tray used in a
method of making a package containing semiconductor devices and
desiccant according to an exemplary embodiment of this invention;
[0016] FIG. 2 is a cross-sectional view of an exemplary tray according
to an exemplary embodiment of the present invention; and
[0017] FIG. 3 is a perspective view showing a hermetically sealed
moisture-proof bag containing a plurality of trays.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0018] These and other features and advantages of this invention
are described in, or are apparent from, the following detailed description
of various exemplary embodiments of the methods according to this
invention.
[0019] This invention was first described in Japanese Patent Application
No. 2002-304458 which is incorporated herein by reference in its
entirety.
[0020] A method of making a package containing semiconductor devices
and desiccant according to an exemplary embodiment of this invention
will be described with reference to the drawings.
[0021] FIGS. 1 and 2 show a tray, that may be used to contain semiconductor
devices and desiccant according to an exemplary embodiment of this
invention. FIG. 1 is a plan view of the tray and FIG. 2 is a magnified
cross-sectional view taken along one end of the tray.
[0022] As shown in FIG. 1 and according to an exemplary embodiment
of the present invention, a rectangular tray 1 has long sides 1a,
short sides 1b, and desiccant retainers 2 for retaining desiccant.
The desiccant retainers 2 are disposed at both ends of the long
side 1a. The center portion of the tray 1 between the desiccant
retainers 2 has pockets 3 for accommodating, or for insertion of,
semiconductor devices. An opening 3a, smaller than the typical size
of the individual package of the semiconductor device, is formed
in the bottom of each pocket 3.
[0023] The tray 1 is made of heat-resistant conductive material,
such as the material described in laid-open Japanese patent application
No. Hei 9-123239 which is incorporated herein by reference in its
entirety. This laid-open patent describes a heat resistant tray
formed by injection molding of heat-resistant resin such as PPE
(poly-phenylene-ether) with a conductive filler such as carbon fibers
or carbon black.
[0024] Each desiccant retainer 2 has a groove 6 (not shown in FIG.
1) extending along the short side 1b of the tray 1. The groove is
covered by a cover 5 having openings 5a arranged in a grid.
[0025] Referring now to the cross-sectional view described in FIG.
2 the desiccant retainer 2 has a groove 6 in which an amount of
silica gel 9 is placed. Protrusions 8 project from the two sidewalls
of the groove 6. The cover 5 having the openings 5a is brought into
engagement with the protrusions 8. The opening 5a is smaller than
the particles of silica gel 9 therefore the silica gel particles
9 are securely retained in the groove 6 once the cover 5 is brought
into engagement with the protrusions 8.
[0026] In other exemplary embodiments of this invention, the placement
and structure of the retainer may be modified. For example, the
cover 5 may be made to fit snugly on the opening of the groove 6.
Furthermore, a heat resistant adhesive may be used as the retainer
to retain the silica gel particles 9 in the groove 6.
[0027] Before the tray 1 is used to ship semiconductor devices,
the desiccant retainers are filled with an appropriate amount of
desiccant that, in an exemplary embodiment of this invention, may
be silica gel particles. Alternatively, the tray 1 may be purchased
from a tray manufacturer with desiccant already present in the retainer.
In another exemplary embodiment of this invention, if the tray 1
is recovered from a customer and still contains desiccant 9 in the
retainer 2 it is not necessary to re-fill the desiccant retainer
2 with desiccant particles 9.
[0028] Semiconductor devices that are encapsulated in individual
plastic packages are subjected to electrical testing and lead inspection,
and then are placed in the pockets 3 of the tray 1 which carry
the desiccant which, in an exemplary embodiment of this invention,
is silica gel. In an exemplary embodiment of this invention, the
tray 1 carrying the semiconductor devices and the silica gel 9 is
heat treated at, for example, 125.degree. C. for approximately six
hours. Upon completion of the heat treatment, the trays designed
to accommodate semiconductor devices and desiccant are stacked,
bound, and sealed in a moisture-proof bag.
[0029] FIG. 3 is a perspective view showing a package that contains
a plurality of trays that carry semiconductor devices and desiccant
(not shown).
[0030] In an exemplary embodiment of this invention, the air inside
the moisture-proof bag 10 containing the trays is removed and the
moisture-proof bag 10 is hermetically sealed. Consequently, a moisture-proof
package 10 containing semiconductor devices and desiccant is made.
[0031] The heat treatment before the sealing of the moisture-proof
package 10 contributes to substantially removing any moisture absorbed
by the individual package. That is, the moisture absorbed in the
plastic individual package is sufficiently removed to an extent
that prevents separation and/or cracking of the individual package
during mounting onto a print-circuit board. Furthermore, in various
exemplary embodiments of this invention, because the desiccant 2
is integral with the tray 1 and is heat-treated together with the
semiconductor devices in the tray 1 the desiccant 9 sealed in the
moisture-proof package 10 together with the semiconductor devices
possesses high moisture absorption capability. Therefore, the environment
inside the moisture-proof bag is kept moisture-free even when the
moisture-proof package is stored for a long period of time in a
humid environment, or the hermetic seal of the bag is defective.
[0032] In other words, the moisture-free environment inside the
moisture-proof package is ensured without any additional care being
necessary to keep the desiccant 9 in a dry environment prior to
the use of the desiccant 9.
[0033] In various embodiments of this invention, the moisture-proof
package 10 is packed in a cardboard box or the like before being
shipped to a customer.
[0034] The trays holding the semiconductor devices that are sent
to customers are collected after the semiconductor devices arc removed
from the trays. Because the trays are collected with silica gel
particles still retained in the desiccant retainers, they can be
reused. That is, the same method of making the moisture-proof package
including placing semiconductor devices on the recovered tray, heat
treating the semiconductor devices and the desiccant retained by
the tray 1 and sealing the heat treated semiconductor devices together
with the heat treated desiccant 9 in a moisture-proof container
10 can be repeated.
[0035] The recovered tray may be used to ship the same semiconductor
devices to the same or different customers, but also may be used
to ship different semiconductor devices to the same or different
customers.
[0036] Because the desiccant 9 and the tray 1 can be used repeatedly,
the amount of chemical waste stemming from the desiccant particles
9 being discarded after each use can be reduced. That is, even if
the desiccant 9 loses its moisture-absorbing ability after repeated
heat treatments and uses, and should be discarded after a certain
number of times of reuse, the total amount of waste can be significantly
decreased compared to a conventional use. Therefore, the burden
of waste control is significantly reduced. The costs incurred from
purchasing the desiccant will also be significantly reduced because
the amount of desiccant 9 to purchase will be greatly reduced.
[0037] While this invention has been described in conjunction with
the exemplary embodiments outlined above, various alternatives,
modifications, variations, improvements, and/or substantial equivalents,
whether known or that are or may be presently unforeseen, may become
apparent to those having at least ordinary skill in the art. Accordingly,
the exemplary embodiments of the invention, as set forth above,
are intended to be illustrative, not limiting. Various changes may
be made without departing from the spirit and scope of the invention.
Therefore, the claims as filed and as they may be amended are intended
to embrace all known or later-developed alternatives, modifications
variations, improvements, and/or substantial equivalents. |