Active solid-state devices (e.g. – transistors – solid-state diode – Combined with electrical contact or lead – Bump leads
Reexamination Certificate
2001-08-01
2003-07-08
Talbott, David L. (Department: 2827)
Active solid-state devices (e.g., transistors, solid-state diode
Combined with electrical contact or lead
Bump leads
C257S778000, C257S780000, C257S781000, C257S783000, C257S787000, C228S180220
Reexamination Certificate
active
06590287
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a packaging method and packaging structure of semiconductor devices such as bare chip with bump formed thereon or chip size package and in particular, a packaging method and packaging structure of semiconductor devices having a resin sealing packaging structure permitting an ease of rework.
2. Description of the Related Art
A flip chip packaging method having a publicly-known solder bump is shown in FIG.
11
(
a
) to FIG.
11
(
d
). As shown in FIGS.
11
(
a
)-(
d
), there has been carried out a method comprising the steps of preparing a semiconductor device (LSI chip)
6
after the formation of a bump
5
and a wiring substrate
1
with a solder
2
formed thereon (FIG.
11
(
a
)); aligning and mounting the semiconductor device
6
on the substrate
1
(FIG.
11
(
b
)) after sticking a flux
9
to the bump tip of the semiconductor device
6
or the substrate
1
; accomplishing the reflow, washing the flux (FIG.
11
(
c
)), then filling an under resin
4
′ into a gap between the semiconductor device
6
and the substrate
1
by dint of capillarity as shown in FIG.
11
(
d
) and finally curing a resin.
Besides, FIGS.
12
(
a
) and
12
(
b
) show a conventional process using no flux. After coating a thermosetting resin of flux action (hereinafter, referred to as active resin
10
) onto a print substrate
1
having a pad
7
coated with solder
2
, as shown in FIG.
12
(
a
), the semiconductor device (LSI chip)
6
after the formation of a bump
5
on a pad
8
is aligned and mounted on the print substrate
1
and thereafter reflow is accomplished as shown in FIG.
12
(
b
), thereby enabling the soldering connection without use of a flux.
Similarly, used as a flip chip packaging method using a gold bump is a method comprising the filling of an under-fill resin after mounting an LSI chip onto a wiring substrate and heat pressuring to electrically connecting the LSI and the wiring substrate via a bump or a packaging method comprising mounting an LSI chip and heat pressuring to cure a resin after coating the resin onto a substrate.
A first problem in a conventional packaging structure and method is that even when the rework of detaching the LSI chip once packaged to a substrate from the substrate and replacing it with a new LSI chip becomes necessary, it is not easy to surely remove the LSI chip fixed by use of a resin and further lead the surface of the chip-mounted substrate to a re-packageable state without the sealing resin left. This is because the sealing resin mainly composed of an epoxy resin is so designed as to lay stress to the assurance of reliability and accordingly the resin itself is so hard, the strength of adhesion to the substrate is so strong that the substrate often ends in being broken when an attempt is made to remove the LSI.
Besides, even if the LSI could be removed without the substrate is broken, the resin left on the substrate surface is firmly stuck and a large elastic modulus, hardness or the like and a mechanical strength due to the influence of a filler added usually on the order of 50-60% or the like makes it difficult to clean the resin off the substrate without damaging the surface thereof.
Thus, with respect to a problem of rework, a sealing resin reputed to be reworkable has been proposed. Concerning the adhesiveness to a substrate under operating environments of below 125° C., this resin has such an adhesion strength as capable of securing the reliability and at operating temperatures of 200° C. or higher as LSI removal temperatures, the adhesion to a substrate lowers and this resin becomes a resin of being LSI removable without breakage of the substrate. In case of this resin, however, compatibility between reliability and reworkability can hardly be obtained. For example, if the filling amount of a filler is lowered so as to facilitate the cleaning of the resin left on a substrate, the thermal expansion coefficient increases simultaneously, and the thermal stress in stretching and contracting a gap between the LSI and the substrate by a heat cycle increases, so that a similar thermal stress is given also to a solder bump, thus lowering the reliability. From these, it is considered not easy to obtain a sealing resin jointly provided with both reliability and reworkability enough for practical use.
Besides, in a conventional flip chip packaging method for connecting a bump by using a flux, there is a tendency to lower the bump height and narrow the gap between the LSI chip and the substrate especially with narrowing pitch due to a higher densitization of LSI, washing of a flux falls into more and more difficult circumstances than a conventional method, and consequently the flux residue becomes at issue still more. As a problem caused by the flux residue, when an active agent remains in electronic parts such as LSI after the flow and this remaining active agent absorbs moisture, its ionic component lowers the electric insulation, thereby causing a problem of deteriorating the reliability of an electronic part produced by migration or the like. In addition to causing a problem of reliability, the filling of under-fill is also hindered, thus causing another problem of lowering the yield of a built-up product such as LSI.
With respect to the problem of a flux residue, use of an active resin has been proposed as a method for the flip chip packaging without use of a flux as shown in FIG.
12
(
a
) and FIG.
12
(
b
). In the above method, however, not only having an active action necessary for the solder joining is required, but involving of air in the area enclosed with a bump is likely to occur and a void is easily generated in case of an LSI having many bumps. Besides, in executing the reflow, an exact control of the package process is demanded for a positional deviation of the LSI caused by buoyancy based on a resin or the like if the quantity of the resin is great. Accordingly, an exact control of resin characteristics such as viscosity is demanded and compatibility between flux actions (removal of a solder oxide film) and physical properties is not easy. Namely, in addition to reliability and reworkability, a further wide exact control is demanded for active actions, viscosity and the like and development of a resin satisfying all these is still more difficult.
On the other hand, various attempts have been proposed to make the reworkability and the reliability compatible. For example, Japanese Patent No. 2924830 specification discloses an arrangement of filling a thermoplastic resin and a thermosetting resin between a semiconductor device and a circuit substrate and at that time, disposing and filling the thermoplastic resin near the center of the gap formed by the semiconductor device and the circuit substrate to join them and sealing the surrounding of the thermoplastic resin with the thermosetting resin to accomplish the resin sealing. If semiconductor devices are inspected prior to the thermosetting resin sealing and revealed to be faulty, heating is made to higher temperatures than the melting point of the thermoplastic resin to remove a faulty semiconductor device and after the whole product become good, a thermosetting resin is filled for sealing and cured to seal the product with a resin. Besides, Japanese Patent No. 2564728 discloses a case of combining resins different in curing conditions such as a photosetting resin and thermosetting resin, a photosetting resin and a spontaneous curing resin or a thermosetting resin and a spontaneous curing resin as the sealing resin. After temporarily fastening a substrate and semiconductor devices under curing conditions of either resin, semiconductor devices are inspected, and a faulty semiconductor is peeled off by soaking the product with a solvent for dissolving the organic resin if found or if the product is good, the other resin is formally cured to complete the resin sealing.
Even for any method, however, an inspection is made in a state of temporary fastening and the rework is possible in this state,
Chambliss Alonzo
NEC Corporation
Talbott David L.
Young & Thompson
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