JP2006272970A - Cleaning method for printing mask - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a cleaning method for printing a mask which effectively cleans the printing mask which prints cream solder on a substrate. <P>SOLUTION: The cleaning method for a printing mask 30 which prints the cream solder on one surface of a substrate includes: a solvent processing step of dropping or spraying solvent 52 from above with a cleaning cloth 50 spread over the upper face of the printing mask 30; and a sucking/cleaning step of removing the deposit on the opening and the surrounding portion of the printing mask 30 by sucking the solvent 52 soaked in the cleaning cloth 50 with a sucking unit 55 arranged below the printing mask 30 while cleaning the lower surface of the printing mask 30 with a dry-type paper 56 after the solvent processing step. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a printing mask cleaning method for printing cream solder on one surface of a substrate.

  In recent years, flip-chip bonding has been cited as a mounting technique necessary for large-capacity, high-speed data communication. Conventionally, the bare chip was directly mounted on the substrate by packaging or face up mainly using the wire bonding method, but the influence of the wire bonding wiring length etc. on the characteristics becomes larger as the frequency increases, There is an increasing need for flip chip bonding that can reduce the wiring length. In addition, it has attracted attention from the viewpoints of downsizing, thinning, and weight reduction of equipment. As a flip chip bonding method, there is a method using ultrasonic waves, a load, and heat, and each method is properly used depending on a bonding material or the like. The main flip chip bonding methods using solder as the bonding material are shown below.

Japanese Patent Laid-Open No. 11-274209 JP-A-11-340270 JP-A-11-297886 JP-A-11-103155 Japanese Patent Laid-Open No. 11-67823 Japanese Patent Laid-Open No. 10-4127 JP-A-8-204322 JP 2001-308268 A

a. Bumps are formed on a wafer on which a circuit is formed by a plating method or a printing method (Patent Documents 1 and 2), and a bare chip is made by cutting into individual pieces. When bonding a bare chip with bumps to a wiring board, flux application is performed on the substrate electrodes or bumps, followed by bare chip mounting and reflow.

b. A bare chip is manufactured by cutting a wafer on which a circuit is formed into individual pieces. At this time, the bump processing is not performed on the bare chip. When connecting the bare chip to the wiring board, supply flux and solder balls to the wiring board in advance (the method of Patent Document 3, solder ball mounting machine, etc.), then place the bare chip on it and reflow the connection. Do.

c. As in Patent Document 4, a solder bump is formed by applying, melting, and curing cream solder in a resist on a substrate to remove the resist.

d. As in Patent Document 5, bumps are formed on a wiring board by plating and etching.

e. As in Patent Document 6, a concave plate filled with a solder paste is stacked on a substrate, and heated and cooled in that state, thereby forming solder bumps on the substrate.

f. As in Patent Document 7, bumps are formed on the substrate by a printing method.

g. As in Patent Literature 8, cream solder is printed on the substrate side by a printing method, a chip with bumps is mounted, and then joined by reflowing.

  A. In this case, since bumps are formed on the wafer after forming the circuit, a wafer of fragile compound semiconductor such as GaAs used for a power amplifier module or the like may cause a microcrack or the like by applying a load to the wafer. Sex is conceivable. In particular, in the case of the printing method, since the pressure is directly applied to the wafer by the squeegee, there is a very high possibility of causing microcracks. Further, the manufacturing cost is increased as compared with the case where no bump is formed.

  B. In this case, bumps are not formed on the wafer, which is advantageous for brittle compound semiconductors. In addition, since the bump processing step does not enter, the cost of the bare chip can be suppressed. However, in order to form bumps, a dedicated solder ball mounting machine or the like is required, which leads to an increase in manufacturing cost as the number of processes increases. In general, in the case of a solder ball mounting machine that is commercially available, an expensive dedicated jig (2 to 3 million yen / 1 jig) is required for each type of product, so a reduction in manufacturing cost cannot be expected.

  C. In this case, the cost for manufacturing the wiring board is increased, and the cost for purchasing the board is increased.

  D. In this case, since it is different from the printed wiring board used conventionally, the cost of the wiring board is increased. Further, bump connection cannot be made to a ceramic substrate or the like on which electrodes and patterns are formed by printing.

  E. In this case, a dedicated intaglio filling with solder paste is required, and the intaglio is also heated together, which increases the heat capacity of the intaglio and heats the substrate. .

  F. In the case of mounting both the bare chip and the surface mount component (SMD) on the wiring board, it is necessary to print again for the surface mount component after performing the bump printing for the bare chip, and the printing process is performed twice. Therefore, it is considered that the number of processes increases and it is difficult to suppress the manufacturing cost.

  G. In this case, since a bare chip with bumps is used, even if the bare chip is a brittle compound semiconductor such as GaAs, it is necessary to form bumps on the bare chip, which may cause micro cracks. Also, when mounting a bare chip, the solder is in an unmelted state, so the solvent component of cream solder can cause capillary action in the gap between the substrate and the bare chip when reflowed, generating bridges and capillary balls (solder balls) Can be considered.

  In recent years, the frequency of circuits has been increased, and a very fragile compound semiconductor such as GaAs has been used as a material of a semiconductor wafer for producing a bare chip. As the frequency increases, it is necessary to shorten the wiring length, which has not been a problem in the past, as much as possible, and the need for flip chip bonding is increasing. In the case of compound semiconductor wafers used for flip chip bonding, micro-cracks and the like may occur if a load is applied during bump processing, etc., so it is important to minimize the load on the wafer as much as possible. .

  Therefore, when mounting both surface mount components such as chip components and bare chips on the substrate, surface mounting is achieved by forming solder bumps on the substrate side for bare chip bonding when mounting surface mount components by solder reflow. It is possible to perform soldering for component bonding and solder for bumps on the substrate at the same time, reducing manufacturing costs and suppressing stress even if the bare chip is a compound semiconductor, etc. It is desired to plan.

  In the above case, a printing mask is used for printing cream solder on the substrate. However, since it is required that the variation in the amount of cream solder applied is small for good bump formation, clean the printing mask after printing. Thus, it is necessary to ensure that the plate removal (the cream solder passes through the opening) is always performed stably.

  Conventionally, as a cleaning device in screen printing, there is Patent Document 9 below, and a structure using a cleaning blade that moves on the lower surface of a screen and air suction by a suction tube is known.

Japanese Patent Laid-Open No. 11-58678

  The objective of this invention is providing the cleaning method of the printing mask which can effectively clean the printing mask which prints cream solder on a board | substrate in view of said point.

  Other objects and novel features of the present invention will be clarified in embodiments described later.

To achieve the above object, the present invention provides a printing mask cleaning method for printing cream solder on one surface of a substrate,
A solvent treatment step of dripping or spraying a solvent from above in a state where a cleaning cloth is laid on the upper surface of the printing mask;
After the solvent treatment step, while wiping the lower surface of the printing mask with dry paper, the solvent soaked in the cleaning cloth is sucked by suction means arranged below the printing mask, and the opening of the printing mask and And a suction cleaning process for removing deposits on the periphery.

  The printing mask may have an opening for printing cream solder on a surface mounting component mounting region and a bare chip mounting region on one surface of the substrate.

  According to the printing mask cleaning method of the present invention, fine printing mask cleaning is possible by wet cleaning cloth, dry paper, and printing mask cleaning using a suction method.

  Hereinafter, as a best mode for carrying out the present invention, an embodiment of a printing mask cleaning method will be described with reference to the drawings.

  As an embodiment of the present invention, a bare chip mounting method and a printing mask cleaning method applied to this method will be described with reference to FIGS.

  FIG. 1 shows a procedure for mounting a surface mount component (SMD) such as a chip component and a bare chip such as a compound semiconductor on a wiring board, and FIG. 2 shows a conventional method a. And conventional method b. FIG. 3 to FIG. 5 show a printing mask, FIG. 6 shows a wiring board support structure, and FIG. 3 to FIG. FIG. 7 shows a method for cleaning a printing mask for cream solder printing.

  In the printing process # 1 in FIG. 2, cream solder printing on the surface mounting component mounting region on one side of the wiring board and cream solder printing on the bare chip mounting region are simultaneously performed using one printing mask (cream soldering). By screen printing). As a result, as shown in FIG. 1A, cream solder printing for surface mount components for mounting the surface mount components (SMD) 20 on the electrode pads 2 and 3 on the upper surface of the wiring substrate 1 such as a resin substrate or a ceramic substrate. The layer 12 is formed in the surface mount component mounting region, and the bump cream solder printing layer 13 for forming the bare chip solder bump is formed in the bare chip mounting region.

  As shown in FIG. 3, the printing mask 30 used in the printing step # 1 has both a surface mounting bonding opening 32 and a bump bonding opening 33. Since it is very small, the amount of solder is controlled by devising the mask thickness, opening shape, and dimensions of the bump bonding opening 33 in the printing mask 30. Half-etching or the like is performed as a method of changing the mask thickness in the periphery of the bump bonding opening 33, thereby obtaining a mask structure having two types of thicknesses with the same mask. That is, the mask thickness of the bump bonding opening 33 is made thinner than the mask thickness of the surface mounting bonding opening 32 so that the cream solder printing layer 12 on the surface mounting component mounting region on the wiring board surface of FIG. The thickness of the cream solder printing layer 13 in the bare chip mounting region is set to be thinner than the thickness.

  As for the opening shape of the printing mask 30, if there are corners of the openings 32 and 33 as shown in FIG. 4A, cream solder particles remain at the corners, leading to variations in the amount of printed cream solder. Therefore, as shown in FIG. 4B, an oval shape with no corners (a shape in which semicircles are connected by parallel straight lines) is adopted to improve the soldering ability of the cream solder, and the cream solder particles in the opening. Make it difficult to remain. However, when there is a margin in the opening pitch, a circular opening may be used.

  With respect to the opening dimensions of the openings 32 and 33 of the printing mask 30, as shown in the case of the circular pad in FIG. 5A, the electrode is formed by the cohesive force at the time of melting the solder as shown in the case of the square pad in FIG. The dimensions were such that the solder printed on the pads 2 and 3 would surely return (1.6 times or less of the pad dimensions (diameter or side)).

  Further, in the manufacturing method of the printing mask 30, one having a small roughness of the inner wall surface of the opening (arithmetic average roughness: about Ra ≦ 0.3 μm) was manufactured to improve the plate slippage. Table 1 below shows values of the wall roughness of the mask opening employed in the present embodiment, and the commonly used SMT additive mask and laser mask wall roughness. However, in Table 1, Ry is the maximum roughness (maximum difference in elevation in the measurement range).

  The opening wall roughness of the printing mask used in the present embodiment needs to be smoother than the additive mask, specifically, Ra <0.84 and Ry <6.54. Preferably, as indicated by “adopted mask” in Table 1, it should be set so that Ra ≦ 0.3 μm is satisfied in both the horizontal and vertical directions.

  The cream solder is a true spherical powder having a particle size of 5 to 15 μm for fine printing, and has a viscosity of 260 ± 30 Pa based on experimental results such as rolling property at the time of printing, shape at the time of plate removal, shape retention after plate removal, etc. It is preferable to use a material that is harder than s and normally used viscosity (around 200 Pa · s). Also on the screen printing apparatus side, it is preferable that the parallel accuracy of the wiring board, the printing mask, and the squeegee run is within R20 μm (the deviation from true parallel is within 20 μm).

  Note that the wiring board supporting and fixing structure is based on the entire surface receiving structure for mounting and fixing the wiring board 1 on the flat surface of the board fixing table 5 in FIG. 6A, or the fixing table 5 in FIG. A point receiving structure in which the supporting means 6 is erected and the wiring board 1 is supported by the supporting means 6 is generally used. However, in this embodiment, the plate omission (the cream solder is opened) by means of cleaning the printing mask after printing. In order to ensure that the process is always performed stably, the substrate fixing table 5 is dug to a depth corresponding to the thickness of the wiring board 1 as in the dug board fixing table of FIG. Forming a substrate support surface 7 that is embedded, the heights of the upper surface of the substrate 1 and the upper surface of the substrate fixing table 5 are the same, and the size of the squeegee for moving the surface of the printing mask and applying the cream solder becomes the printed material Larger than the board width By employs a completely scraping method in a wide range from the wiring substrate size cream solder on the printing mask by a squeegee. As a result, cleaning from the upper surface of the printing mask is possible.

  As shown in FIG. 7, the cleaning method for the printing mask is to apply the cleaning cloth 50 on the printing mask 30 that contacts the wiring board and cover the entire opening formation region of the mask 30. A lower part provided with a suction unit 55 and a dry paper 56 from the lower side of the mask 30 and a take-up means 57 after executing a solvent treatment step in which a solvent 52 is uniformly dropped (or sprayed) from the nozzle 51 onto the cloth 50. The unit 58 is moved along the lower surface of the mask, and the solvent 52 soaked in the cloth 50 is sucked by the suction unit 55, and the solder particles and flux adhering to the opening and its peripheral portion are wiped and removed by the dry paper 56. (Suction removal step). Thereafter, the cleaning cloth 50 on the upper portion of the mask 30 is withdrawn and left to stand naturally or dried with air, nitrogen gas or the like to finish cleaning.

  The surface mounting component 20 is mounted on the wiring board 1 of FIG. 1A after simultaneously printing the surface mounting component bonding solder and the bump bonding cream solder by screen printing of the cream solder in the printing process # 1 of FIG. By passing through a reflow furnace and executing solder reflow, solder bonding of the surface mount component 20 to the wiring board 1 and solder bumps 23 are simultaneously formed as shown in FIG. That is, a bare chip mounting substrate having the solder bumps 23 is obtained.

  3 through 6 and Table 1 and the soldering cream to be used, and the effect of improving the printing loss by adopting the cleaning method of the printing mask in FIG. The defect (bridge, etc.) and the variation in the amount of solder were suppressed, and bump formation with a bump diameter of 100 μm, a pitch of 200 μm, and a bump height variation of 10 μm or less was made possible by the cream solder printing method. As a result, it was possible to realize a method for simultaneously printing surface mount components and bump solder.

  In addition, bumps having a diameter of 100 μm and a pitch of 200 μm are formed by the above method using Pb-free solder (lead-free solder) that has recently been used as an environmental measure. Confirmed that it was possible.

  As shown in FIG. 1B, after soldering the surface mount component 20 to the wiring board 1 and forming the solder bumps 23 at the same time, an appearance inspection is performed as shown in FIG. After applying the bare chip mounting flux, bare chip mounting process # 2 is executed, and the electrode pads 41 of the bare chip 40 without bumps are placed on the solder bumps 23 facing downward (the electrode pads 41 face the bumps 23). In this state, by passing through a reflow furnace and executing solder reflow, the bare chip 40 is flip-chip bonded (face-down solder bonding) onto the wiring substrate 1 as shown in FIG.

  After that, if necessary, both surface mounting components and bare chips are mounted on the wiring board through cleaning, underfill (adhesive material filling the gap between the bare chip and wiring board), underfill curing, and inspection. Parts are obtained.

  According to the present embodiment, a screen printing apparatus that has been used conventionally and a printing mask that smoothes the inner wall surface roughness of the mask opening (preferably Ra ≦ 0.3 μm) and suppresses variation in the amount of solder are used. Then, solder paste for surface mounting components is finished on the board by printing cream solder for bump formation and surface mounting component bonding at the same time, and mounting and reflowing surface mounting components in the subsequent process It is possible to form a state in which a very small solder bump for chip bonding is formed. In this method, solder for flip chip bonding is supplied to the substrate side in the SMT printing process, and bumps are formed by reflow, so even bare chip of fragile compound semiconductor such as GaAs used for power amplifier modules etc. Flip chip mounting is possible without bump processing on the side. Therefore, the load on the wafer side can be reduced, and expensive dedicated equipment and jigs are not required, so that the manufacturing cost can be reduced.

  Further, by cleaning the printing mask 30 with the wet cleaning cloth 50, the dry paper 56 and the suction unit 55 shown in FIG.

  Although the embodiments of the present invention have been described above, it will be obvious to those skilled in the art that the present invention is not limited to these embodiments, and various modifications and changes can be made within the scope of the claims.

It is embodiment of this invention, Comprising: It is explanatory drawing which shows the mounting procedure of surface mounting components and a bare chip. It is a mounting process flow figure of the surface mounting components and bare chip in an embodiment of the invention. It is sectional drawing of the printing mask used in embodiment of this invention. It is an opening shape of a printing mask, (A) is a conventional shape, (B) is a top view which shows the opening shape of this Embodiment. It is an opening dimension of the printing mask used by this Embodiment, Comprising: (A) is a top view which shows the example of an opening dimension corresponding to the case where an electrode pad is circular and (B) is an electrode pad square. A method for fixing a wiring board, wherein (A) is a side view of a substrate fixing table having a full surface receiving structure, (B) is a side view of a substrate fixing table having a point receiving structure, and (C) is employed in the present embodiment. It is a sectional side view of a digging board | substrate fixed table. It is a block diagram which shows the printing mask cleaning method in embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Wiring board 2,3,41 Electrode pad 5 Board | substrate fixing table 6 Support means 12 Cream solder printing layer for surface mount components 13 Cream solder print layer for bumps 20 Surface mount component 23 Solder bump 30 Print mask 32 Opening for surface mount bonding 33 Bump bonding opening 40 Bare chip 50 Cleaning cloth 51 Nozzle 52 Solvent 55 Suction unit 56 Dry paper 58 Lower unit

Claims (2)

A printing mask cleaning method for printing cream solder on one side of a substrate,
A solvent treatment step of dripping or spraying a solvent from above in a state where a cleaning cloth is laid on the upper surface of the printing mask;
After the solvent treatment step, while wiping the lower surface of the printing mask with dry paper, the solvent soaked in the cleaning cloth is sucked by suction means arranged below the printing mask, and the opening of the printing mask and A cleaning method for a printing mask, comprising: a suction cleaning step for removing deposits on the periphery.   The printing mask cleaning method according to claim 1, wherein the printing mask has openings for printing cream solder on a surface mounting component mounting region and a bare chip mounting region on one surface of the substrate.

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