JP2673764B2 - Resin-sealed semiconductor device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a resin-encapsulated semiconductor device, and more particularly to a resin-encapsulated semiconductor device which has excellent solderability and is compatible with a large number of leads and a fine pitch.

[0002]

2. Description of the Related Art Resin sealing technology has been widely used as a package technology for protecting a semiconductor element from an external environment and facilitating mounting on a printed circuit board. However, the integration density of semiconductor elements has been increasing four times in three years, and the element size has been increasing accordingly. In addition, the number of pins is rapidly increasing with the high integration, high performance, and multi-functionalization of devices.

On the other hand, from the needs of miniaturization, weight reduction, and high performance of various electronic equipments, it is strongly desired that various semiconductor devices have high packaging density, and the package of semiconductor parts is in the trend of miniaturization and thinning. In addition, the package shape is DIP (Dual Inline Plastic Package) which mounts the pin by inserting it into the through hole of the printed circuit board, ZIP.
(Zigzag Inline Plastic Package), SIP (Singl
From the so-called pin insertion type such as e Inline Plastic Package) to SOP (Small Outline Plastic Package)
e), SOJ (Small Outline J-lead Plastic Package
), A double-sided mounting such as QFP (Quad Flat Plastic Package) is possible, and the demand for a small surface mounting type package is rapidly increasing. Mounting of such semiconductor components on a printed circuit board is usually performed by soldering.

[0004]

However, as the number of pins increases with higher integration and higher functionality of devices, miniaturization of packages is required, resulting in finer leads and finer pitch. Various technical problems have come to occur when mounting (soldering) on a printed circuit board. That is, when a component having an extremely narrow lead interval is mounted on a printed circuit board, solder bridging occurs between adjacent leads, which easily causes a problem of short-circuiting the leads. This is for the following reason. Conventionally, in order to facilitate the soldering of a resin-sealed semiconductor to a printed circuit board, the outer lead is solder-plated when the resin sealing of the element is completed. However,
The solder-plated lead frame has good wettability with the solder, so when you try to solder this onto the printed circuit board, the lead frame absorbs the solder previously applied to the circuit part of the board, Since the solder plated on the frame melts and flows, there are some areas of the lead frame where the amount of solder is abnormally high.
This was because the lead short-circuited at that part.

In order to deal with such a problem, attempts have recently been made to seal a semiconductor with a resin by using a lead frame whose surface is thinly plated with palladium. This is because the lead frame plated with palladium has extremely good wettability with solder, but since palladium itself does not melt during soldering, abnormal thickening of the lead frame due to excessive soldering is unlikely to occur. , Even if the lead pitch is narrowed, the lead is short-circuited due to solder bridging between adjacent leads.
Is less likely to occur.

However, in the resin-encapsulated semiconductor device using such a palladium-plated lead frame, the solder wettability of the leads is remarkably changed with time, and the solder wettability is lowered as the heating and humidification treatment steps are performed. However, the solution has become an important technical issue in applying the lead frame plated with palladium to the resin-sealed semiconductor. The present invention has been made in view of such circumstances, and an object of the present invention is to provide a resin-encapsulated semiconductor device having excellent solderability corresponding to a multi-pin lead and a fine pitch. It is a thing.

[0007]

[Means for Solving the Problems] In order to solve the above problems, a detailed analysis was conducted on the reason why the solder wettability of a lead frame plated with palladium changes with time. As a result, the reason why solder wettability decreases is that during resin encapsulation, free phenol generated from the encapsulating material adheres to the surface of the lead frame, which is altered by the catalytic action of palladium, which causes solder wettability. It has become clear that Therefore, it has been clarified that it is necessary to reduce the amount of free phenol generated from the encapsulating material in the encapsulation step in order to suppress the change in solder wettability of the lead frame plated with palladium over time. The present invention has been accomplished in view of such circumstances, and the main points are as follows.

That is, a part of the lead frame and the semiconductor element in which the electrodes on the surface of the semiconductor element fixed to the die pad portion or the inner lead of the lead frame and the inner lead are electrically connected are (a) epoxy resin,
(B) a phenolic resin curing agent, in the resin sealing type semiconductor device encapsulated with the resin composition and (c) a curing accelerator and (d) a non-KiTakashi Hamazai essential components, the lead frame is a printed circuit board At least the tip end portion electrically connected to is covered with a plating film containing palladium as a main component or an outermost layer, and the resin composition is a phenol resin.
Two or more phenolic hydroxyl groups in the molecule as a fat curing agent
Free phenol containing less than 1 wt%
Nitrogen-containing compound as a curing accelerator
The amount of free phenol generated in the sealing step of 30 to 180 seconds at 150 to 190 ° C. is 30 pp.
It is supposed to be m or less. In the above, it has good that the leadframe is copper or copper-based alloy.

[0009]

The phenolic resin currently used as a curing agent for epoxy resin-based semiconductor encapsulation materials is synthesized by the addition condensation reaction of phenol and formalin. Therefore, unreacted phenol remains in the resin. Therefore, the source of free phenol is considered to be the phenolic resin of the curing agent. Therefore, in order to reduce the amount of free phenol generated, it is first important to reduce the amount of unreacted phenol contained in the phenolic resin. However, it is technically and economically limited to extremely reduce the amount of unreacted phenol. On the other hand, the encapsulating material undergoes thermal decomposition of the resin component in the encapsulation process, and free phenol is also generated by such thermal decomposition of the resin component. Therefore,
In order to reduce the amount of free phenol generated, it is important to suppress the thermal decomposition of such resin components.

In the present invention, by using a nitrogen-containing compound as a curing accelerator, the release of free phenol contained in the phenolic resin to the outside of the system can be suppressed, and at the same time, the heat of the resin component generated in the sealing step can be suppressed. It also suppresses decomposition. Examples of the nitrogen-containing compound that can be used in the present invention include imidazole, 1-methylimidazole, 2-
Ethyl-4-methylimidazole, 1-cyanoethyl-
2-ethyl-4-methylimidazole, 1-cyanoethyl-2-undecylimidazole, 1-cyanoethyl-
2-phenylimidazole, N-benzyldimethylamine, 2,4,6-tris (dimethylaminomethyl) phenol, tetramethylbutylguanidine, pyridine, N
-Methylpiperazine, piperidine, 1,8-diazabicyclo (5,4,0) -7-undecene or their derivatives, and organic acid salts and organic boron salts of each compound can be used.

The epoxy resin used for the encapsulating material of the present invention is not particularly limited in its structure, but is an o-cresol novolac type epoxy resin, a bifunctional or polyfunctional epoxy resin using bisphenol A as a raw material, naphthalene or A bifunctional or polyfunctional epoxy resin having a biphenyl skeleton can be used. As the phenol-based curing agent, in addition to phenol novolac resin, o-
Phenolic resins such as cresol novolac resin, poly-p-vinylphenol, and a condensation product of phenol and aralkyl ether can be used. As the inorganic filler, fused silica, crystalline silica, alumina or the like can be used. In addition to the above, a coupling agent, a release agent, a colorant, a flame retardant, a softening agent and the like can be added as required.

Each of these materials can be kneaded into a sealing material by using a twin-screw roll or an extruder. The thus obtained sealing material can be used for resin sealing of a semiconductor by using a transfer press in the same manner as the conventional method. The lead frame used for the resin-encapsulated semiconductor device of the present invention is preferably copper or a copper-based alloy. For example, iron-based lead frames are not practical when the surface is plated with palladium, because the corrosion resistance of the lead frames is significantly reduced. When palladium plating is applied to the copper-based lead frame, for example, nickel plating may be applied to the base in order to improve the adhesion between the layers. The thickness of the palladium plating of the outermost layer is not particularly limited, but is at least 0.1 μm.
It is desirable to have a thickness of m or more.

Next, FIG. 6 to FIG. 8 show the relationship between the amount of phenol generated in the mold sealing step and the solder wetting defect rate of the lead frame. 6 to 8, the amount of phenol generated is the amount of phenol (ppm) generated when the sealing step is performed by heating at 180 ° C. for 90 seconds, and FIG. 6 shows the secondary cure, that is, after heating at 180 ° C. for 5 hours. Is a graph showing the solder wetting failure rate (%) of FIG. 7, FIG. 7 is a graph showing the solder wetting failure rate (%) after baking, that is, after 168 hours at 150 ° C., and FIG. 8 is 100 ° C., 100%. It is a graph which shows a solder wetting failure rate (%) after humidification for 16 hours under relative humidity. As can be seen from these figures, when the amount of phenol generated in the sealing step is 30 ppm or less, the solder wetting failure rate is 0% after any of the treatments, and a semiconductor device sealed with such a sealing material is used. Is clearly superior. Note that a to e indicate materials corresponding to the resins a to e in the examples.

[0014]

EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited thereto. Example 1 First, an example of a sealing material used in the present invention will be described. Resin Example a As an epoxy resin, 85 parts by weight of an o-cresol novolac type epoxy resin and 15 parts by weight of a brominated bisphenol A type epoxy resin, and 52 parts by weight of a phenol novolac resin having a free phenol content of 0.5 wt% as a curing agent. Part, 1.5 parts by weight of 1,8-diazabicyclo (5,4,0) -7-undecene as a curing accelerator, and a molecular weight of about 80 having amino groups at both ends as a flexibilizer,
000 polydimethylsiloxane 8 parts by weight, 350 parts by weight of fused silica as a filler, 2 parts by weight of epoxysilane as a coupling agent, 1 part by weight of montanic acid ester as a release agent, and trioxide as a flame retardant aid. 10 parts by weight of antimony and 1 part by weight of carbon black as a colorant were weighed. Then, each of these materials was kneaded for about 15 minutes using a biaxial roll heated to about 80 ° C. to produce a target sealing material.

Resin Example b A sealing material was prepared in the same manner as in Resin Example a except that 85 parts by weight of tetramethylbiphenol type epoxy resin was used as the epoxy resin.

Resin Example c Free phenol content of 0.35 wt% as a curing agent
A sealing material was prepared in the same manner as in the above resin example a except that 95 parts by weight of the phenol aralkyl resin in Example 1 was used.

Resin Example d (Comparative Example) Resin Example a above except that a phenol novolac resin having a free phenol content of 1.5 wt% was used as a curing agent.
A sealing material was prepared in the same manner as in.

Resin Example e (Comparative Example) A sealing material was prepared in the same manner as in Resin Example a except that 1.5 parts by weight of tetraphenylphosphine was used as a curing accelerator.

Next, the structure of the semiconductor device to which the present invention is applied will be described with reference to the drawings. FIG. 1 shows that after the semiconductor element 1 is fixed to the leads 3 via the film-shaped double-sided adhesive 2, the electrodes 4 on the elements and the inner leads 3 are electrically connected by the gold wires 5, and then the elements and the inner leads are connected. It is an example of SOJ sealed with the sealing material 6. Palladium plating 7 is applied to the outer leads. In FIG. 2, the semiconductor element 1 is fixed to the die pad portion 8 of the lead frame with the silver paste 9, and the electrode 4 on the element and the inner lead 3 are electrically connected with the gold wire 5, and then the element and the inner lead are sealed. TSOP (Thin Small Outline Plasti) sealed with Material 6
c Package). The outer leads are plated with palladium as described above.

FIG. 3 shows the appearance in which the leads (3 and 3 ') to which the semiconductor elements (1 and 1') are fixed are joined to form a two-tier semiconductor element, which is resin-sealed with a sealing material 6. Is SO
This is an example of J (Small Outline Plastic Package). The outer leads are plated with palladium as described above. The amount of free phenol generated when the encapsulating materials of the five resin examples a to e produced as described above were heated at 180 ° C. for 90 seconds was measured using gas chromatography. Further, the semiconductor device shown in FIG. 1 is resin-sealed with the sealing materials of the above resin examples a to e, and the solder wettability of the lead frame immediately after sealing, after post-curing, and after further heating and humidification treatment. Was evaluated. The solder wettability was judged to be good when the poor solder wettability (solder repelling) portion of the lead frame was within 5% of the surface area, and when it was 5% or more. Table 1 summarizes the evaluation results.

[0021]

[Table 1] As is clear from Table 1, the sealing material of the present invention has a small amount of free phenol generated in the sealing step. Further, it can be seen that the resin-encapsulated semiconductor device does not deteriorate in solder wettability even after the post-curing and subsequent heating and humidification treatment steps for a long time.

FIG. 4 shows a semiconductor device using a lead frame plated with palladium according to the present invention when soldered to a printed circuit board, and FIG. 5 shows a semiconductor device using a conventional lead frame plated with solder. It is a result of comparing the degree of solder attachment to the lead frame when soldering is performed on the. In the conventional semiconductor device using a lead frame plated with solder (Fig. 5), the solder pre-attached to the printed circuit board is sucked up and the solder around the lead frame adheres a lot, so the lead frame looks thick. In the semiconductor device (FIG. 4) using the palladium-plated lead frame of the present invention, lead thickening due to excessive soldering is hardly recognized.

[0023]

As described above, the lead frame plated with palladium of the present invention has little change in solder wettability with time, has good solderability at the time of mounting on a substrate, and has a narrow lead pitch. It can be seen that it is suitable for advanced multi-pin devices.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view showing an example of a semiconductor device of the present invention.

FIG. 2 is a schematic cross-sectional view showing another example of the semiconductor device of the present invention.

FIG. 3 is a schematic cross-sectional view showing another example of the semiconductor device of the present invention.

FIG. 4 is a partially enlarged view of the lead frame of the present invention soldered to a substrate.

FIG. 5 is a partially enlarged view of a conventional lead frame soldered to a substrate.

FIG. 6 is a graph showing the relationship between the amount of phenol generated and the solder wetting failure rate.

FIG. 7 is a graph showing the relationship between the amount of phenol generated and the solder wetting failure rate.

FIG. 8 is a graph showing the relationship between the amount of phenol generated and the solder wetting failure rate.

[Explanation of symbols]

1, 1 ': semiconductor element, 2: double-sided adhesive, 3, 3': lead, 4: electrode, 5: gold wire, 6: sealing material, 7: palladium plating, 8: die pad part, 9: silver paste ,
10: Solder, 11: Printed circuit board

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Reference number within the agency FI Technical display location H01L 23/31 H01L 23/30 R H05K 1/18 (72) Inventor Shuji Eguchi Hitachi City, Ibaraki Prefecture 4026 Kujimachi, Hitachi, Ltd.Hitachi Laboratory (72) Inventor Hiroyuki Hozoji, 4026 Kujimachi, Hitachi, Hitachi, Ibaraki Prefecture Hitachi, Ltd., Hitachi Research Laboratory (56) References JP-A-2-298056 (JP, A) JP-A-2-175747 (JP, A)

Claims (2)

(57) [Claims] 1. A semiconductor element in which an electrode on a surface of a semiconductor element fixed to a die pad portion or an inner lead of a lead frame and an inner lead are electrically connected to each other and a part of the lead frame are provided with (a) an epoxy resin, b) a phenolic resin curing agent, in the resin sealing type semiconductor device encapsulated with the resin composition and (c) a curing accelerator and (d) no KiTakashi <br/> Hamazai the essential components, the lead frame Is at least the tip portion electrically connected to the printed circuit board is covered with a plating film containing palladium as the main component or the outermost layer,
Moreover, the resin composition is a phenolic resin curing agent.
Contains two or more phenolic hydroxyl groups in the molecule, and
Phenolic tree containing less than 1 wt% of phenol
Use fat and nitrogen-containing compounds as curing accelerators
The resin-encapsulated semiconductor device is characterized in that the amount of free phenol generated in the encapsulation process at 150 to 190 ° C. for 30 to 180 seconds is 30 ppm or less. 2. The resin-encapsulated semiconductor device according to claim 1, wherein the lead frame is made of copper or a copper-based alloy.