JP2007149998A - Printed circuit board for mounting flat package electronic part and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a printed circuit board where inexpensive material is applied by printing between lands of narrow pitch, and to provide its manufacturing method so as to solve the problem wherein solder resist is not capable of being applied by a printing method between the lands of narrow pitch in the printed circuit board mounted with so-called narrow pitch leads whose lead pitch is 0.4 mm or below, and therefore, if high-accuracy photosensitive solder resist is used in place with the usual solder resist, the photosensitive solder resist is high in material cost, and furthermore its equipment is expensive. <P>SOLUTION: In the printed circuit board, printing ink is applied between the narrow-pitch lands to form a bridge preventing part. The method of manufacturing the printed circuit board is carried out through such processes of covering around a land group composed of a large number of lands with solder resist, and applying character ink between the lands, using a mesh screen where a mesh knitting direction is tilted by an angle of 45° toward a hole bored in a printing block, so as to form the bridge preventing part. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a printed circuit board on which a flat package type electronic component such as a QFP or SOP, particularly a flat package type electronic component having a narrow lead pitch, and a method for manufacturing the same.

  Since today's electronic devices have been miniaturized, the electronic components incorporated in the electronic devices have also become smaller. The most prominent are surface mount components. Surface mount components include chip types such as chip capacitors and chip resistors, and flat package types such as QFP, SOIC, SOP, and QFJ. In particular, a flat package type surface mount component greatly contributes to miniaturization of electronic devices because it has many functions in one main body.

  QFP and SOIC have many leads on the four sides of the main body, and SOP and QFJ have many leads on the two sides of the main body. Solder paste is used to solder these flat package type electronic components (hereinafter, representatively referred to as QFP) to a printed circuit board. When soldering the printed circuit board and the QFP, first, a solder paste is printed on the land of the printed circuit board, and the QFP is mounted on the application part. Thereafter, the solder paste is melted by heating with a heating device such as a reflow furnace, and the QFP lead and the printed circuit board land are soldered. For this reason, the printed circuit board must have lands formed exactly where it coincides with the QFP leads.

  The printed circuit board on which this QFP is mounted must have heat resistance that does not deform or burn when soldered with solder paste, as well as insulation. In the past, ceramics and glass were used as the insulating base material for forming printed circuit boards. However, since the materials themselves are expensive and are difficult to handle because they are difficult to handle, the insulating bases of organic resins have recently been used. Many materials are used. Examples of insulating base materials for organic resins include phenol, epoxy, melamine, silicon, polyester, diallyl phthalate, and the like. Since these organic resin insulation base materials do not have sufficient mechanical strength, the resin is not used as it is, and is based on paper, nylon cloth, polyester cloth, glass fiber, and impregnated with resin. Strength has been improved.

  By the way, as an electronic device, an insulating base material called “Gala Epoch” in which glass fiber is impregnated with an epoxy resin is used in computers and communication equipment that value reliability, but the insulating base material of Gala Epoe is expensive. In so-called consumer equipment such as televisions, videos, and portable DVD playback devices that are inexpensive and mass produced, inexpensive “paper / phenol” is used. This paper / phenol is obtained by impregnating paper with a phenol resin.

In general, a QFP-mounted printed circuit board with a wide lead pitch is manufactured through the steps shown in FIG.
(A) Copper foil pasting process on insulating base material Copper foil 2 is pasted on one side of insulating base material 1. Copper foil is manufactured by rolling or electroforming. Many of the copper foils used in consumer electronic devices have a thickness of 35 μm. This copper foil is affixed to an insulating substrate with an adhesive such as phenol resin or epoxy resin.
(B) Etching resist application | coating process on copper foil The etching resist 3 is apply | coated to the part used as the land on the copper foil 2 by the printing method. As the etching resist, a modified rosin resin, an acrylic resin, a phenol resin, or the like is used, and many are applied on the copper foil by a printing method.
(C) Copper foil etching step The copper foil portion on which the etching resist 3 on the insulating substrate 1 is not applied is dissolved and removed with an etching solution. As an etching solution for dissolving the copper foil, a ferric chloride solution, a cupric chloride solution, or the like is used.
(D) Etching resist removal process The etching resist 3 is dissolved and removed with a solvent to form lands 4. When the etching resist is ink, a sodium hydroxide aqueous solution is used as the removal solvent.
(E) Solder resist application process The solder resist 5 is applied to the portions other than the land 4 by a printing method. The solder resist is applied to all parts other than the lands, that is, between the lands. As the solder resist, an epoxy melamine thermosetting type is often used. The thickness of the solder resist is appropriately selected according to the application, but when the land thickness is 35 μm, the thickness is about 20 μ, which is thinner than that. The solder resist thickness is made thinner than the land thickness. When solder paste is printed on the land during soldering, the solder paste can be printed more reliably when the land protrudes above the solder resist. Because.
(F) Character printing process Characters and symbols 6 are printed on the solder resist 5 at necessary locations by a printing method. Character ink is used for printing characters and symbols, but UV curable ink is the mainstream for character ink.

  The application state of the solder resist on the conventional printed circuit board will be described with reference to FIGS. 7 is a partially enlarged plan view of the printed circuit board manufactured in FIG. 6, and FIG. 8 is an enlarged partial perspective view of the same. A solder resist 5 is applied on the insulating substrate 1 in all parts other than the lands 4. Of course, the solder resist 5 is also applied between the lands 4 and the adjacent lands 4. In addition, characters and symbols 6, such as the name of the QFP (“IC5” in FIG. 7, “5” in FIG. 8, etc.) mounted in the vicinity of the land on which the QFP is mounted, are printed with character ink at the necessary locations on the solder resist 5. The name of the manufacturer of the electronic device (“SMIC” in FIG. 7) is also printed in the corners on the insulating base 1 with character ink.

  By the way, the printed circuit board obtained by the etching resist removal step (D) of the printed circuit board manufacturing method, i.e., the insulating substrate on which the land is formed and the solder resist is not applied is used as it is as the printed circuit board. it can. However, on a printed circuit board with only lands formed, when solder paste is applied to the lands and then heated in a reflow furnace to melt the solder paste, the molten solder flows out between the lands, The flux soaks into the insulating substrate.

  When the molten solder flows out between the lands, it fuses with the molten solder of the adjacent lands to form a bridge between the lands. Since the bridge between lands becomes a short circuit and impairs the function of the electronic device, a bridge must never be formed between the lands.

  When the flux soaks into the insulating base material, it forms bubbles during soldering and adheres between the lands. If the foam-like flux adheres between the lands in this way, the inspection of the soldered portion performed after soldering will be hindered. That is, the inspection of the soldered portion of the printed circuit board is generally performed visually, but since the minute soldered portion cannot be visually inspected, the image recognition inspection is performed by the inspection apparatus. At this time, if bubbles are formed between the lands, the inspection device recognizes the bubbles as solder and causes an inspection error.

  Further, when the flux soaks into the insulating base material, the flux absorbs moisture after soldering and causes a decrease in insulation resistance between lands. When the insulation resistance between the lands decreases, an electronic device incorporating the printed circuit board cannot exhibit a sufficient function. Therefore, in order to prevent the penetration of the bridge and the flux during soldering, it is necessary to apply a solder resist at places other than the lands of the insulating base material, that is, between the lands.

  In general, the method of applying a solder resist to an insulating substrate is roughly classified into two types: a method by screen printing using a paste solder resist and a method of exposing and developing using a photosensitive solder resist.

  Conventionally, many solder resist coating methods have been performed by screen printing. This screen printing method is inexpensive, but is not suitable for a pattern having a narrow space between lands because of insufficient positional accuracy. On the other hand, a photosensitive solder resist that applies photographic resolution has high positional accuracy and the boundary of the solder resist is clear, so that it is possible to form a solder resist between narrow lands. However, this method is not suitable for consumer equipment because the photosensitive material itself used is expensive and the process is complicated and the manufacturing cost is high.

  By the way, the QFP generally used in electronic equipment has a lead pitch (interval between the center of the lead and the adjacent lead) of 0.6 mm or more (referred to as a wide pitch lead), and the QFP lead gap (lead adjacent to the lead). The gap is 0.3 mm. In this way, if a printed circuit board is mounted with QFP with wide pitch leads, it is possible to print and apply a solder resist between the leads by a printing method. In other words, in the printed circuit board for mounting QFP with wide pitch leads, the prevention part (hereinafter referred to as the bridge prevention part) that prevents bridging between lands or prevents flux from penetrating (hereinafter called bridge prevention part) The solder resist can be applied all at once when printing and applying. However, with the recent miniaturization of electronic devices, the QFP is also becoming smaller, and the lead pitch of the miniaturized QFP is a narrow pitch lead of 0.4 mm or less. This narrow pitch lead gap is 0.2 mm, but if you try to apply a solder resist as a bridge prevention part to the 0.2 mm land gap by the printing method, the printing method has insufficient positional accuracy, so the soreda resist is on the land. In some cases, it may adhere to each other or may not be applied accurately between lands.

Conventionally, a thermosetting resin or a photosensitive solder resist has been applied between lands on a printed circuit board having narrow pitch lands (Patent Documents 1 and 2). In the printed circuit board of Patent Document 1, after the copper foil etching step, a thermoplastic resin is applied by spraying or a roller coater with the etching resist remaining on the copper foil. Moreover, the printed circuit board of patent document 2 prints and coats a photosensitive solder resist on an insulating substrate, and then forms a thick photosensitive dry film solder resist on the photosensitive solder resist applied between lands. The solder resist is formed between the lands by pasting, exposing and developing.
JP-A-6-260747 Japanese Patent Laid-Open No. 10-112580

  As mentioned above, when applying a solder resist between narrow lands on a printed circuit board with a QFP with a lead pitch of 0.4mm or less, the printing method is not accurate enough. It cannot be used because it is not applied accurately. On the other hand, a photographic development type photosensitive solder resist is excellent in accuracy, but is not suitable for a printed circuit board of an inexpensive consumer electronic device because the material is expensive and the process is complicated. The present invention is a printed circuit board for mounting QFP with a lead pitch of 0.4 mm or less, in which a bridging prevention part is formed with an inexpensive material between lands, and bridge prevention is also achieved between printing lands with a narrow pitch. An object of the present invention is to provide a printed circuit board manufacturing method capable of applying a material having an effect and an effect of preventing flux penetration.

  After applying solder resist, character printing is performed such as marking the part name on the solder resist near the land, marking the mounting direction of the part with a symbol, and further marking the manufacturer name. Like the solder resist, the character ink used for the ink has the property of preventing the molten solder from flowing or preventing the flux from penetrating into the insulating base material, and the character ink. Has completed the present invention by paying attention to the fact that if a special screen is used, printing can be performed between lands having a narrow pitch.

  The present invention provides a flat package type electronic component mounting printed circuit board in which a plurality of rectangular lands are arranged on an insulating base material at a pitch of 0.4 mm or less and a land group is formed by these lands. The periphery of the group is covered with a solder resist, and between the lands of the land group, character ink having a color different from that of the resist is applied by screen printing to form a bridge prevention portion. A printed circuit board for mounting a flat package type electronic component.

  In another invention, a plurality of rectangular lands are arranged side by side with a pitch of 0.4 mm or less on an insulating base material, and a land group is formed by these lands, and the rectangular lands are formed on a printed circuit board. In a method for manufacturing a printed circuit board for mounting a flat package type electronic component, which is installed so as to be parallel or orthogonal to each side and coated with a solder resist on an insulating base material, After coating with solder resist, using a mesh screen knitted with a mesh inclined 45 degrees with respect to each side of the rectangular plate hole, the ink for characters with a different color from the solder resist at the necessary locations on the solder resist In addition to printing characters and symbols on the screen, printing ink is applied between each land of the land group to form a bridge prevention part. It is a manufacturing method of a printed circuit board for mounting a package type electronic component.

  Although the printed circuit board of the present invention uses an inexpensive material such as paper or phenol, a bridge prevention portion is formed between lands having a narrow pitch, so that solder paste is applied on the lands. However, even if heating is performed after the QFP is mounted on the application part, the molten solder does not flow and form a bridge between adjacent lands, and the flux flowing outside the land penetrates the insulating base material. Therefore, the insulation resistance between the lands is not lowered during the use of the electronic device. In addition, the printed circuit board manufacturing method of the present invention is capable of printing character ink having an effect of preventing bridging and preventing flux penetration between narrow pitch lands, which is impossible with conventional screen printing. The printed circuit board thus manufactured can produce a printed circuit board having excellent reliability that does not cause the formation of a bridge or a decrease in insulation resistance.

  In the present invention, in the case of a portion where a large number of lands are arranged in parallel, that is, a land of a printed circuit board on which a QFP is mounted, a large number of lands that coincide with the leads on one side of the QFP are referred to as a land group. In this case, the solder resist is not applied, but the ink for printing is applied by a printing method to form the bridge preventing portion.

  The character ink applied between the lands in the present invention prevents the flow of the molten solder and does not soak the flux in the solder paste, and the character ink generally used has these characteristics. . In addition, the character ink used in the present invention has a color different from that of the solder resist. If the ink for characters is a different color from the solder resist, not only will the characters be easier to read when the characters are printed on the solder resist, but it will also be distinguished from the solder resist when inspecting the printed state between the lands after printing. It becomes easy to do. Since most of the solder resists are green, the color ink is preferably a color opposite to green, such as white and yellow.

  The printed circuit board which is the subject of the present invention is one in which rectangular lands are formed in parallel with each side of the rectangular printed circuit board. In a screen on which character ink is screen-printed between lands of the printed circuit board, the plate holes are also parallel to each side of the printed circuit board. Therefore, when the character ink is printed and applied between the lands, the plate holes are parallel to the direction of travel of the squeegee that scrapes and smoothes the character ink placed on the screen.

  In general, after applying the solder resist, characters and symbols are printed on the necessary places on the solder resist by a printing method. The screen used here has mesh stitches parallel to the direction of squeegee travel during printing. It is. However, with this screen, even if an attempt is made to print character ink between lands having a narrow pitch, a necessary amount of ink cannot be printed between lands. The reason is that if the mesh of the character printing screen is at right angles to the pattern, the mesh thread will be in the way, making it difficult for the ink for the character to come out, so that it will not smoothly enter between the patterns.

  Therefore, in the present invention, a screen as shown in FIG. 5 is used. A plate hole 10 is formed in the screen 9 at a position that coincides with the land between the printed circuit boards. The plate hole has a long side slightly narrower than between the lands of the printed circuit board, and slightly longer than the long side of the land of the printed circuit board. In the plate hole 10, there is a mesh 11 knitted into a mesh, and the mesh direction of the mesh 11 is inclined 45 degrees with respect to the squeegee traveling direction (white arrow) during printing. In this inclined stitch screen, as shown in FIG. 5, the mesh in the narrow plate hole is inclined 45 degrees. Therefore, even if the ink filled in the plate hole is orthogonal to the traveling direction of the squeegee, the mesh yarn is obstructive. do not do. As a result, the inclined stitch screen can easily apply the character ink between the patterns.

  The present invention will be described below with reference to the drawings. FIG. 1 is a diagram for explaining a manufacturing process in a method for manufacturing a printed circuit board according to the present invention, FIG. 2 is a plan view of the printed circuit board according to the present invention, and FIG. FIG. 4 is an enlarged perspective view of the printed circuit board after character ink is printed in the process of the manufacturing method of the present invention. Note that an actual printed circuit board on which a narrow pitch QFP is mounted has 40 or more lands in one land group, but the number of lands is smaller than the actual one on the drawing for convenience of understanding.

First, a method for producing a printed circuit board according to the present invention will be described. FIG. 1 is a diagram for explaining the steps of a printed circuit board manufacturing method according to the present invention. The same parts as those in the conventional manufacturing method of FIG.
(A) Copper foil pasting process on insulating substrate
(B) Etching resist coating process on copper foil
(C) Copper foil etching process
(D) Etching resist removal process
(G) Step of applying solder resist around the land group The solder resist 5 is applied to a portion other than the land group 7 formed by the plurality of lands 4. In a narrow pitch printed circuit board, the distance between the lands is so narrow that the solder resist cannot be accurately applied by the printing method. Therefore, here, the solder resist is not applied between the lands.
(H) Application process of printing ink on solder resist and between lands. Ink for character is applied to necessary parts on solder resist 5, and mesh as shown in FIG. The type of electronic component and the manufacturer name 6 of the electronic device are printed by the printing method using the clean, and at the same time, the ink for characters is applied between the lands 4 of the land group 7 to form the bridge preventing portions 8.

  Here, the solder resist coating step and the character ink printing step in the manufacturing method of the present invention will be described in more detail with reference to FIGS. The solder resist is not applied between the lands 4 as shown in FIG. 3 because the solder resist is not accurately applied between the lands having a narrow pitch by the printing method. Is applied around the land group (portion surrounded by the alternate long and short dash line) 7. And the necessary parts on the solder resist, such as the type of QFP to be mounted on the land (“IC7” in FIG. 2, “7” in FIG. 4), the manufacturer name of the electronic device (“SMIC” in FIG. 2), etc. At the same time as character printing, character ink is printed between the lands 4. Then, as shown in FIG. 4, the bridging prevention part 8 is formed with printing ink between lands.

  In the printed circuit board of the present invention and a printed circuit board having a narrow pitch land and no solder resist applied between the lands, solder paste is applied on the land of these printed circuit boards, and QFP is mounted on the application part, and then reflow is performed. The land and QFP lead were soldered by heating in a furnace. When the soldered part was observed with a stereomicroscope, no bridge was generated between the lands in the printed circuit board of the present invention, and no foaming phenomenon was observed between the lands. On the other hand, in the printed circuit board in which the solder resist is not applied between the lands, bridges frequently occur between the lands, and many foams are observed between the lands.

The figure explaining the manufacturing process in the manufacturing method of the printed circuit board of this invention Plan view of the printed circuit board of the present invention The expansion perspective view of the printed circuit board before printing the ink for characters in the process of the manufacturing method of this invention The expansion perspective view of the printed circuit board after printing the character ink in the process of the manufacturing method of the present invention The top view of the screen which prints a character on the printed circuit board of this invention The figure explaining the manufacturing process in the manufacturing method of the conventional printed circuit board Plan view of a conventional printed circuit board Partial enlarged perspective view of a conventional printed circuit board

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Insulation base material 2 Copper foil 3 Etching resist 4 Land 5 Solder resist 6 Character and symbol 7 Land group 8 Bridge prevention part 9 Screen 10 Plate hole 11 Mesh

Claims (2)

  In a flat package type electronic component mounting printed circuit board in which a plurality of rectangular lands are arranged side by side with a pitch of 0.4 mm or less on an insulating substrate, and a land group is formed by these lands, around the land group The flat package is characterized in that a solder resist is coated, and between the lands of the land group, character ink having a color different from that of the resist is applied by screen printing to form a bridge prevention portion. PCB for mounting electronic components. A plurality of rectangular lands are arranged in parallel at a pitch of 0.4 mm or less on the insulating base material, and lands are formed by these lands, and the rectangular lands are parallel to each side of the printed circuit board or In a method for manufacturing a printed circuit board for mounting a flat package type electronic component in which a solder resist is applied on an insulating base material that is installed so as to be orthogonal to each other, after the periphery of the land group is covered with the solder resist, Using a mesh screen with a mesh knitted at 45 degrees with respect to each side of a rectangular plate hole, characters and symbols are screen-printed with a character ink different in color from the solder resist at the necessary locations on the solder resist. In addition, a flat package type electronic component is provided, wherein a bridging prevention portion is formed by applying printing ink between the lands of the land group. Manufacturing method of printed circuit board for mounting.

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