JP3456598B2 - Tie bar forming resin composition - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mold resin flow stop tie bar paste for a lead frame used in a resin-sealed semiconductor element.

[0002]

2. Description of the Related Art Generally, a resin-encapsulated semiconductor element is formed by adhering a semiconductor chip to a lead frame, wire bonding, and then encapsulating with a molding resin. Usually, this lead frame is provided with a tie bar on the outside of a portion to be a molded product of the lead frame in order to prevent the flow of an extremely small amount of molding resin flowing out from the mating surface of the molding die and the lead frame.

The operation of the tie bar will be described with reference to the drawings. FIG. 1 is a schematic view showing two sides of the lead frame 1. The lead frame 1 is provided with a tie bar 2 for preventing the molding resin from flowing out from the mating surface of the molding die and the lead frame, outside the portion of the lead frame 1 which is to be a molded product. FIG. 2 shows a schematic diagram in which the mold resin is filled. The mold resin 5 is filled as burrs from the mold line 4 and further between the tie bar leads.
FIG. 3 is a schematic diagram showing a state after the mold resin 5 filled between the mold line 4 and the tie bar 2 in FIG. 2 is punched and removed together with the tie bar 2 by a die press.

With the recent increase in the size and density of semiconductor elements and the increase in the number of leads, the spacing between lead wires is becoming narrower, and the punching method using a die press is reaching its limit. That is, the dimensional accuracy of the mold and the wear due to the press are increased, and the life of the expensive mold is shortened, which leads to an increase in the cost of the entire package. Therefore, a method of forming a lead frame without a tie bar in advance and forming a tie bar made of an insulating organic material on the lead frame (for example, Japanese Patent Application Laid-Open Nos. 1-241850 and 2).
-122660) has been proposed. There are two methods for forming the tie bar on the lead frame by using an insulating organic material. First, as in the conventional method, a tie bar is formed on the outside of the part to be a molded product using an insulating organic material, and it is removed in a later step. This is a method of forming a tie bar using an organic material and integrating it with a mold resin.

In the former case, the following characteristics are required for the tie bar organic material. 1) It is possible to fill the space between the leads without any gaps 2) No deformation or outgassing due to the temperature at the time of bonding the semiconductor element to the lead frame and wire bonding 3) Mold resin molding temperature, molding pressure and mold compression pressure To withstand the flow of mold resin 4) No deformation or compression deformation of leads due to mold clamping pressure 5) Easy removal after molding The latter characteristics are: 1) Fill the gap between the leads without gaps 2) 3) Same as above 4) Tie bar can be formed at accurate position 5) Excellent adhesion to mold resin and no leakage current between leads when absorbing moisture. Further, in consideration of productivity in addition to the above-mentioned respective characteristics, as an organic material for a tie bar, the light disclosed in JP-A-3-218032 is disclosed. Curable resin, JP-A-62-15
A heat resistant tape represented by the Teflon tape disclosed in Japanese Patent No. 8351 can be used. As the photocurable resin, an ultraviolet curable resin is generally used. However, in the above publication, no specific resin is exemplified and the characteristics are not clear.

[0006]

DISCLOSURE OF INVENTION Problems to be Solved by the Invention The present invention has been made as a result of the examination of resins applied to a method of removing after molding.
Formability of tie bar on lead frame, low outgassing,
The present invention has been completed by finding a resin composition for a tie bar, which has an excellent ability to prevent the mold resin from flowing and which can be easily removed by applying pressurized water after molding the mold resin.

[0007]

The present invention is directed to a diacrylate represented by the formula [1], a photosensitizer , a thixotropic agent and an average particle size.
A resin composition for a tie bar, which contains a spherical filler having a particle size of 10 μm or less as an essential component, and contains 50% by weight or more of the diacrylate represented by the formula [1] in all acrylates.

[0008]

[Chemical 2] R: Aliphatic residue, oxygen or sulfur m, n is 0 or an integer of 1 or more, 5 ≦ m + n

In the resin composition of the present invention, as for the diacrylate having the above structure, in the formula [1], R is an aliphatic residue, oxygen or sulfur, and m and n are 0 or 1.
The above integer is 5 ≦ m + n, but the total number of oxyethylene chains (m + n) must be 5 or more. 5
If it is less than the above range, the compressive deformation is large at the time of molding, and the removability by water jet etc. is poor. The upper limit of m + n is not particularly limited, but is preferably 50 or less. When it exceeds 50, the resin is too soft and moldability is poor. Also, it is difficult to obtain from the market. R is an aliphatic residue, oxygen or sulfur, of which isopropylidene is preferred. Further, if the amount of diacrylate in the total acrylate resin is less than 50% by weight, the characteristics such as flexibility and removability of the diacrylate, which is an essential component of the present invention, cannot be utilized. When used together for the purpose of decreasing viscosity, improving heat resistance, improving curability, etc., examples of the acrylate include 1,6-hexanediol diacrylate,
Neopentyl glycol diacrylate, polypropylene glycol diacrylate, polyethylene glycol diacrylate, trimethylolpropane triacrylate, dipentaerythritol hexaacrylate, pentaerythritol triacrylate, tetramethylolmethane tetraacrylate, polyfunctional urethane acrylate, etc. It is not something that will be done.

Examples of the photosensitizer used in the present invention include, but are not limited to, Michler's ketone compounds, thioxanthone compounds, benzophenone compounds and benzoin ether compounds. The thixotropic agent used in the present invention is, for example, an ultrafine filler having a submicron particle size such as Aerosil (trade name) is added to impart thixotropic properties. This makes it possible to form tie bars on the lead frame by dispensing, screen printing, or the like. However, since the resin structure of the present invention contains a hydrophilic diethylene glycol group in the main chain, the thixotropic agent used preferably has a hydrophobic surface. This is because when the surface is hydrophilic, the resin and the thixotropic agent interact with each other and sufficient thixotropic properties cannot be obtained. Further, a small amount of a thiol compound or an amine compound can be added to enhance the curability. Further, a filler such as silica may be added to improve the strength of the tie bar. The filler used at this time is preferably a spherical filler having an average particle diameter of 10 μm or less in order to prevent the lead frame from being compressed and deformed. Furthermore, the amount of addition is 70% of the total composition in consideration of the curability of the composition.
It is preferably not more than weight%. If it exceeds 70% by weight, the paste viscosity increases and it becomes difficult to form it on a lead frame by printing or the like.

[0010]

The UV-curable resin composition of the present invention acts as a flow stop for the mold resin, and the cured product has an appropriate softness depending on the molding temperature.
Since there is no compression deformation of the lead wire, the outer lead can be bent without any trouble. Furthermore, since it has a hydrophilic structure, it can be pressurized with water such as a water jet after molding.
The tie bar can be easily removed. The paste of the present invention contains a diacrylate represented by the formula [1], a photosensitizer and a thixotropic agent as essential components, but if necessary, an additive such as a curing accelerator, a filler and an antifoaming agent is preliminarily added. It can be manufactured by mixing and kneading using a triple roll.

EXAMPLE 1 The present invention will be described below with reference to Examples. In the formula [1], m + n = 10, R is isopropylidene, 100 parts by weight of diacrylate, and Irgacure 184 (Ciba Geigy) as a photosensitizer. 3 parts by weight, 15 parts by weight of a spherical silica filler having an average particle diameter of 1 μm as a filler, and 10 parts by weight of Aerosil R-805 (manufactured by Nippon Aerosil Co., Ltd.) as a thixotropic agent were kneaded to prepare a resin composition for tie bar. This paste has a thickness of 125 μm,
On a QFP copper frame with a pitch of 0.3 mm and a number of leads of 344, a thickness of 30 μm and a line width of 0.
Printed through a screen in a 3 mm wax pattern, 80 W /
A high pressure mercury lamp of cm ² was irradiated from a height of 15 cm for 1 minute to cure. Next, a semiconductor element was mounted on the die pad using silver paste and wire bonding was performed. Resin sealing was performed using an epoxy mold resin. The mold resin was completely stopped at the tie bar. Finally, the tie bar could be completely removed by honing with high pressure water. After the tie bar was removed, the lead wire was not compressed or deformed at all. Example 2 A resin composition was prepared in the same manner as in Example 1 except that a diacrylate in which m + n = 17 in the formula (1) and R was isopropylidene was used, and the same moldability and removability were examined, and the same results were obtained. Results were obtained. Example 3 Moldability and removability were examined in the same manner as in Examples 1 and 2 except that a diacrylate in which m + n = 30 in the formula (1) and R was isopropylidene was used, and similar results were obtained.

Comparative Example 1 The same evaluations as in Example 1 were carried out except that in formula (1), m + n = 4 and diacrylate in which R was isopropylidene was used. As a result, the lead was pressed and deformed, and was bent, which was not practical. Comparative Example 2 Example 1 except that m + n = 17 in the formula (1), 40 parts by weight of diacrylate in which R is isopropylidene, 20 parts by weight of neopentyl glycol diacrylate, and 40 parts by weight of trimethylolpropane triacrylate were used. A tie bar resin composition was prepared in the same manner as in. Further, resin sealing was performed in the same manner. The mold resin was completely stopped at the tie bar. However, the honing treatment with high-pressure water could only remove the high-pressure water enough to deform the lead wire. (However, there was no compression deformation of the lead wire that could be removed.) Comparative Example 3 In Example 1, the average particle diameter of the spherical silica filler was 15
The same evaluation as in Example 1 was performed except that the thickness was set to μm. Good moldability and removability, but 10 μm on lead wire
Some degree of dimple-like deformation was observed, which was not practical.

[0013]

According to the present invention, a resin tie bar for performing inexpensive molding resin molding can be formed on a multi-pin lead frame with high productivity.

[Brief description of drawings]

FIG. 1 is a schematic view of two sides of a lead frame.

FIG. 2 shows a schematic diagram in which a mold resin is filled.

FIG. 3 is a schematic diagram showing a state after the mold resin filled between the mold line and the tie bar is punched and removed by a die press together with the tie bar.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI H01L 23/50 H01L 23/50 J Y (58) Fields investigated (Int.Cl. ⁷ , DB name) C08F 2/00-2 / 60 G03F 7/004-7/031 H01L 21 / 56,23 / 50

Claims (3)

(57) [Claims] 1. A diacrylate represented by the formula [1], a photosensitizer , a thixotropic agent, and a spherical filler having an average particle size of 10 μm or less.
Is an essential component, and the diacrylate represented by the formula [1] is contained in an amount of 50% by weight or more in all acrylates. [Chemical 1] R: Aliphatic residue, oxygen or sulfur m, n is 0 or an integer of 1 or more, 5 ≦ m + n 2. The resin composition for a tie bar according to claim 1, wherein R in the formula [1] is isopropylidene. 3. The resin composition for tie bars according to claim 1 or 2, wherein the surface of the thixotropic agent is hydrophobic.