JP4840390B2 - Semiconductor package and manufacturing method thereof - Google Patents

Description

  The present invention relates to a semiconductor package on which solder balls are mounted, and a manufacturing method thereof.

  In recent years, with the demand for higher functionality and lighter, thinner and smaller electronic devices, high-density integration and further high-density mounting of electronic components have progressed. Semiconductor packages used in these electronic devices have been In addition, the size and number of pins are increasing.

With the miniaturization of semiconductor packages, the conventional package using a lead frame has a limit on miniaturization. Therefore, recently, it is assumed that a chip is mounted on a circuit board, and BGA (Ball Grid) is used. Array) and a new area mounting type packaging method such as CSP (Chip Scale Package) have been proposed. In these semiconductor packages, various insulating materials such as plastics and ceramics called semiconductor mounting substrates, which have the functions of the electrodes of the semiconductor chip and the lead frame of the conventional semiconductor package, and the terminals of the substrate composed of conductor wiring, As an electrical connection method, a wire bonding method, a TAB (Tape Automated Bonding) method, FC (Flip)
(Chip) method and the like are known, but recently, BGA and CSP structures using the FC connection method, which are advantageous for miniaturization of semiconductor packages, have been actively proposed.

  Solder bonding using bumps formed of solder balls is employed for mounting BGA and CSP on a printed wiring board. For this soldering, a flux is used, and a solder paste may be used in combination. The reason why the solder balls are used in particular is that the amount of solder supply can be easily controlled and a large amount of solder can be supplied, so that the bump can be made high. Also, solder bonding is often used for the electrical connection method between the electrodes of the semiconductor chip and the terminals of the semiconductor mounting substrate in the manufacturing process of the BGA or CSP.

  In general, for solder bonding, dirt on the surface of the electrode against the solder surface such as oxide on the metal surface is removed, and re-oxidation of the metal surface during solder bonding is prevented to reduce the surface tension of the solder. The soldering flux is used to make the molten solder wet easily on the metal surface. As this flux, a flux obtained by adding an activator for removing an oxide film to a thermoplastic resin flux such as rosin is used.

  However, if this flux remains, problems such as a decrease in electrical insulation and corrosion of printed wiring, such as melting of the thermoplastic resin at high temperature and high humidity, and liberation of active ions in the activator occur. For this reason, currently, the residual flux after soldering is removed by washing to solve the above problems, but there are disadvantages such as environmental problems of the cleaning agent and cost increase due to the cleaning process.

  As described above, the flux functions include removal of oxides on the solder and metal surfaces, prevention of re-oxidation, and improvement of solder wettability (reducing surface tension). The flux is present and the metal surface is exposed. If so, the solder gets wet without any restrictions. Therefore, generally, a solder resist is used on the circuit surface of a semiconductor package or a printed wiring board in order to introduce solder only into the solder joint and to protect the conductor wiring pattern. However, if this solder resist remains in the solder joint, there arises a problem that connection reliability is lowered or solder joint cannot be performed. Therefore, careful attention is required for forming the solder resist.

  In addition, downsizing and increasing the number of pins of a semiconductor package promotes miniaturization of solder balls, and there is a concern that bonding strength and reliability may be reduced. Therefore, in order to obtain the reliability of the bump connection part, studies are being made to seal and reinforce the solder ball connection part by filling the gap between the chip and the substrate with an insulating resin called underfill. However, this requires a process of filling and curing an underfill with a high technical difficulty, and thus has a problem that the manufacturing process is complicated and the manufacturing cost is increased.

  In view of such a current problem of solder bonding at the time of mounting a semiconductor package, the present invention does not require cleaning and removal of residual flux after solder bonding and filling with underfill, etc., even in a high temperature and high humidity atmosphere. It is an object of the present invention to provide a method for manufacturing a semiconductor package that retains electrical insulation and enables solder bonding with high bonding strength and reliability, and a semiconductor package obtained by the manufacturing method.

That is, in the present invention, a photosensitive flux capable of forming a flux pattern at a predetermined position by exposure and development is applied to the entire surface of the circuit pattern on the surface on which the solder balls of the semiconductor package are mounted, dried, and exposed. Forming a conductive flux film, placing a predetermined pattern on the photosensitive flux film, exposing and developing, and forming a flux pattern on a land portion for mounting a solder ball of a semiconductor package, the flux pattern The method includes a step of placing a solder ball on the surface and soldering the solder ball to a land for mounting a solder ball of a semiconductor package by solder reflow, and a step of heat-treating the solder ball-mounted semiconductor package to cure the photosensitive flux. Semiconductor package manufacturing method characterized by the above, and obtained by the manufacturing method It is a semiconductor package that.

  In the present invention, a preferable photosensitive flux includes a resin (A) having at least one phenolic hydroxyl group, a resin (B) that acts as a curing agent thereof, and a photosensitive agent (C) having an orthoquinonediazide structure as essential components. It is characterized by that.

  In the manufacturing method of the present invention, the photosensitive flux used for this does not require cleaning and removal of the residual flux after soldering, and maintains electrical insulation even in a high temperature and high humidity atmosphere. Since the periphery is cured in a form that reinforces it in a ring shape, it enables solder bonding with high bonding strength and reliability, simplifying the process of mounting a semiconductor package on a printed wiring board, and suppressing manufacturing costs, Also, it is extremely useful for improving the reliability of solder joints. Further, by imparting photosensitivity, this flux can be selectively left only in the solder mounting portion, and aggregation of the solder balls due to the interfacial tension with the solder balls can be prevented.

The photosensitive flux used in the present invention only needs to be able to form a flux pattern at a predetermined position by exposure and development. Among them, the photosensitive flux (A) having at least one phenolic hydroxyl group, and acting as a curing agent thereof. The photosensitive flux containing the resin (B) and the photosensitizer (C) having an orthoquinonediazide structure as essential components is preferable, and the positive type flux is mentioned here.

Further, the phenolic hydroxyl group of the resin (A) having at least one phenolic hydroxyl group used in the present invention removes dirt such as solder and oxide on the surface of the metal by its reducing action, and flux for soldering. Acts as This phenolic hydroxyl group is not restricted at all, but in order to enhance the action as a solder bonding flux, the resin (A) having a phenolic hydroxyl group has an electron at the ortho- and para-positions relative to the phenolic hydroxyl group. Those having an attractive group and an electron donating group at the meta position are preferred.

  Furthermore, since a good cured product can be obtained by the resin (B) that acts as the curing agent, there is no need for cleaning and removal after solder bonding, electrical insulation is maintained even in a high temperature and high humidity atmosphere, Enables highly reliable solder joints.

  The resin (A) having at least one phenolic hydroxyl group used in the present invention is a phenol novolak resin, an alkylphenol novolak resin, a biphenol novolak resin, a naphthol novolak resin, a resorcinol novolak resin, a resole resin, or a polyvinyl phenol resin. At least one selected from the above is preferred, and among these, those having a weight average molecular weight of 20000 or less are preferable. If the molecular weight is too large, the fluidity of the photosensitive flux at the time of solder bonding is lowered, which hinders solder bonding. However, there is no problem if the melt viscosity at the time of soldering can be controlled to 50 Pa · s or less by using other compounding agents. For this purpose, a liquid curing agent may be blended or a solvent may be added.

  Regarding the alkylphenol novolac resin, the alkyl group preferably has about 1 to 4 carbon atoms, such as a methyl group, an ethyl group, an n-butyl group, a sec-butyl group, a tert-butyl group, and an allyl group. When the number of carbons exceeds that, it is not preferred because of increased lipophilicity and alkali developability.

  The blending amount of the resin (A) having at least one phenolic hydroxyl group is preferably 20 to 80% by weight of the entire photosensitive flux. If it is less than 20% by weight, the action of removing dirt such as solder and oxides on the metal surface is lowered, and solder bonding cannot be performed. On the other hand, if it is more than 80% by weight, a sufficient cured product cannot be obtained, and the bonding strength and reliability are lowered. The photosensitive flux of the present invention, which has a balance between melt viscosity, oxide removability and curability, is cured in a form that reinforces the periphery of the solder joint in a ring shape, so it is compared with conventional solder joints using flux. Thus, the bonding strength and reliability can be greatly improved.

  As resin (B) which acts as a hardening | curing agent of resin (A) which has a phenolic hydroxyl group used for this invention, an epoxy resin, an isocyanate resin, etc. are used. Specifically, all are based on phenol-based ones such as bisphenol, phenol novolac, alkylphenol novolac, biphenol, naphthol and resorcinol, and skeletons such as aliphatic, cycloaliphatic and unsaturated aliphatic And modified epoxy compounds and isocyanate compounds. Moreover, in order to accelerate the curing of the photosensitive flux used in the present invention, a known curing catalyst can be further used.

  The photosensitizer (C) comprising a compound having an orthoquinonediazide structure used in the present invention is a photosensitizer widely used for positive photosensitive resins, and sulfonate esters of naphthoquinonediazide are commonly used but are not limited. There is no place. The solubility of the resin (A) having a phenolic hydroxyl group in an alkaline developer alone is suppressed by the addition of a photosensitizer (C) having an orthoquinonediazide structure, but the exposed portion is dissolved because an indenecarboxylic acid is generated by a photoreaction. Is promoted to enable pattern formation.

The blending amount of the photosensitive agent (C) having an orthoquinonediazide structure is preferably 3 to 30% by weight of the entire photosensitive flux. When the blending amount of the photosensitizer (C) is too large, the concentration of diazo per unit volume increases, the light transmittance decreases due to coloring, and more light is required for photolysis. On the contrary, if the blending amount of the photosensitizer (C) is too small, the development stability is lowered. The photosensitive flux used in the present invention based on the appropriate selection of the resin (A) having a phenolic hydroxyl group and the optimum blending amount of the photosensitive agent (C) having an orthoquinonediazide structure has a desired amount at a predetermined position. Since flux supply is possible, problems such as poor solder connection due to insufficient flux supply and excessive solder bridges can be solved, which is particularly suitable for fine solder connection.

  As a method for producing a semiconductor package of the present invention, the photosensitive flux component is made into a varnish of a photosensitive flux with an organic solvent such as alcohols, ethers or ketones, and this is mounted on a solder ball of the semiconductor package. A photosensitive flux layer is formed on the entire surface of the circuit pattern by applying it by a method such as screen printing or spin coating, followed by drying. Next, the pattern is aligned and laminated on the photosensitive flux layer, exposed to an actinic ray such as a high-pressure mercury lamp or a metal halide lamp, and developed with an aqueous alkali solution such as sodium hydroxide or tetramethylammonium hydroxide. Then, a flux pattern is formed at a predetermined position of the solder ball mounting land of the circuit pattern, the solder ball is placed on the flux pattern, and the solder ball is soldered to the solder ball mounting land by solder reflow. Thereafter, the photosensitive flux layer is cured by further heating, and the periphery of the solder joint can be reinforced with a photosensitive flux resin in a ring shape.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to these at all.

Example 1.
100 g of m, p-cresol novolac resin (Nippon Kayaku Co., Ltd. PAS-1, OH group equivalent 120), bisphenol F type epoxy resin (Nippon Kayaku Co., Ltd. RE-404S, epoxy group equivalent 165) 140 g, And 20 g of diazonaphthoquinone (NQD-1 manufactured by Nippon Kayaku Co., Ltd.) are dissolved in 60 g of cyclohexanone, 0.2 g of 2-phenyl-4,5-dihydroxymethylimidazole is added as a curing catalyst, and a photosensitive flux varnish is prepared. Produced. The obtained photosensitive flux varnish was applied on a 125 μm thick copper plate, dried at 80 ° C. for 10 minutes to form a 20 μm thick photosensitive flux film, and then the resolution of the photosensitive flux film was evaluated. As a result, an exposure amount of 200 mJ / cm ² with a high-pressure mercury lamp and development for 1 minute with 2.5% tetramethylammonium hydroxide (TMAH) had a resolution of line / space = 20/20 μm.

Example 2
In place of 100 g of m, p-cresol novolak resin used in Example 1, 100 g of bisphenol A type novolak resin (LF 4781 manufactured by Dainippon Ink & Chemicals, Inc., OH group equivalent 120) was used. In the same manner as above, a photosensitive flux varnish was prepared. The resolution of this photosensitive flux film was line / space = 30/30 μm.

Example 3
Instead of 100 g of m, p-cresol novolak resin and 140 g of bisphenol F type epoxy resin used in Example 1, phenol novolak resin (manufactured by Sumitomo Durez Co., Ltd., PR-51470, OH group equivalent 105) and diallyl bisphenol A type A photosensitive flux varnish was prepared in the same manner as in Example 1 except that 210 g of epoxy resin (Nippon Kayaku Co., Ltd., RE-810NM, epoxy group equivalent 220) was used. The resolution of this photosensitive flux film was line / space = 30/30 μm.

Comparative Example 1
A curable flux varnish was produced in the same manner as in Example 1 except that diazonaphthoquinone was not blended in Example 1.

The following evaluation was performed about each using the flux varnish obtained above.
1. Solder ball shear strength test Using a 125 μm thick copper plate (EFTEC64T, manufactured by Furukawa Electric Co., Ltd.), an evaluation circuit including a land diameter of 300 μm and a land pitch of 0.5 mm was formed, and the lead frame was sealed with a semiconductor After mold-sealing with a material (EME-7372 manufactured by Sumitomo Bakelite Co., Ltd.), polishing was performed from one side to expose the evaluation circuit, and a 10 mm square evaluation package was produced. For the polishing finish, water-resistant polishing paper No. 1000 specified in JIS-R6252 was used. This was washed with isopropyl alcohol and then dried at 80 ° C. for 30 minutes to obtain a solder joint evaluation package.

The photosensitive flux varnish obtained in Examples 1 to 3 and the curable flux obtained in Comparative Example 1 were applied to the entire surface of the evaluation circuit exposed surface of the evaluation package, and dried at 80 ° C. for 10 minutes. Thus, a flux film having a thickness of 20 μm was formed. In Examples 1 to 3, a predetermined pattern was placed on the photosensitive flux film, and exposure was performed at a dose of 200 mJ / cm ² using a high-pressure mercury lamp exposure apparatus. Next, development was performed with a 2.5% TMAH aqueous solution at a spray pressure of ² Kg / m ² to form a photosensitive flux having a diameter of 400 μm on the land. As another comparative example of Comparative Example 1, a commercially available solder flux (MSP511 manufactured by Kyushu Matsushita Electric Co., Ltd.) was applied. Reflow with a peak temperature set to 240 ° C. after mounting 60 350 μm diameter solder balls (Sn—Pb eutectic solder, manufactured by Senju Metal Mining Co., Ltd.) on each evaluation circuit package land The solder balls were joined to the evaluation package through a furnace. Thereafter, Examples 1 to 3 and Comparative Example 1 were heat treated at 150 ° C. for 60 minutes to cure the photosensitive flux and the curable flux. For the commercial flux, an evaluation package on which a solder resist was formed was also prepared.

  Next, the solder ball shear strength (using a universal bond tester PC2400T manufactured by Daisy) of the obtained evaluation package with solder balls was measured. The average value of 60 was obtained for each, and the results are summarized in Table 1. In addition, as a comparative example using a commercially available solder flux, Comparative Example 2 was used when the solder resist was not formed, and Comparative Example 3 was an evaluation package with solder balls formed with the solder resist.

2. Temperature cycle test The same commercially available flux as described above was applied to a printed wiring board for temperature cycle (TC) test, and the evaluation package with solder balls of Examples and Comparative Examples was mounted, and the peak temperature was set to 240 ° C. Through the reflow furnace thus manufactured, 10 package mounting substrates for evaluation were produced. The evaluation package mounting board is designed so that 60 solder ball joints are connected in series via the evaluation package and the test printed wiring board.

  After confirming the continuity of the obtained package mounting substrate for evaluation, a TC test was performed in which one cycle was 10 minutes at -50 ° C and 10 minutes at 125 ° C. The results of the number of disconnection failures after 1000 cycles of the TC test are summarized in Table 1. Further, a solder resist was formed as a comparative example, and a sample filled with underfill was also prepared as Comparative Example 4. About Comparative Examples 2-4, after mounting the package for evaluation, it was washed with isopropyl alcohol and used.

3. Insulation resistance test Using a printed wiring board for insulation reliability test having a comb-shaped pattern with a conductor spacing of 150 μm subjected to solder plating, the photosensitive flux varnish obtained in Examples 1 to 3 and Each of the curable fluxes obtained in Comparative Example 1 was applied and dried at 80 ° C. for 10 minutes to form a 20 μm thick flux film. About Examples 1-3, it exposed also by the irradiation amount of 200 mJ / cm < ² > using the high pressure mercury lamp exposure apparatus. As Comparative Examples other than Comparative Example 1, a test printed wiring board coated with the same commercially available flux as described above was also prepared. After passing through a reflow furnace set at a peak temperature of 240 ° C., Examples 1 to 3 and Comparative Example 1 were heat-treated at 150 ° C. for 60 minutes to cure the flux to obtain a test printed wiring board.

  After measuring the insulation resistance of this printed wiring board, a DC voltage of 50 V was applied in an atmosphere of 85 ° C./85%, and the insulation resistance after 1000 hours was measured. The applied voltage at the time of measurement was 100 V for 1 minute, and the insulation resistance was summarized in Table 1. In the comparative example using the commercially available flux, the flux was not washed, and the comparative example 5 was used.

  As can be seen from the evaluation results shown in Table 1, when the photosensitive flux of the present invention is used, the solder ball shear strength is about twice as high as that of the conventional flux, In the TC test, the occurrence of disconnection failure was almost eliminated. The insulation resistance test shows almost no decrease, and the effect of the photosensitive flux of the present invention is clear.

Claims (4)

A process of applying a photosensitive flux capable of forming a flux pattern at a predetermined position by exposure and development to the entire surface of the circuit pattern on the surface on which the solder balls of the semiconductor package are mounted, and drying to form a photosensitive flux film. A step of placing a predetermined pattern on the photosensitive flux film, exposing and developing, and selectively forming a flux pattern on a land for mounting solder balls of a semiconductor package, leaving the photosensitive flux film Mounting a solder ball on the flux pattern and soldering the solder ball to a solder ball mounting land of a semiconductor package by solder reflow; and heat-treating the solder ball mounting semiconductor package to cure the photosensitive flux A method of manufacturing a semiconductor package comprising the steps of: The photosensitive flux has as essential components a resin (A) having at least one phenolic hydroxyl group, a resin (B) acting as a curing agent thereof, and a photosensitive agent (C) comprising a compound having an orthoquinonediazide structure. The method of manufacturing a semiconductor package according to claim 1. 3. The method of manufacturing a semiconductor package according to claim 1, wherein the photosensitive flux is cured in a form in which the solder ball joint is reinforced with resin. The semiconductor package obtained by the manufacturing method in any one of Claims 1-3.