JP2002176249A - Printed board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a printed board in which printability of solder paste and mountability of an electronic device having solder bumps, e.g. BGA, CSP, and the like, are enhanced and reliability of a mounted electronic device module is improved. SOLUTION: In the printed board 1 for mounting an electronic device having solder bumps, the group of through holes 3 proximate to mounting pads 2 for connection with the solder bumps of the electronic device is covered collectively with an insulating material 4. Marking ink (silk), solder resist or an insulation film is used as the coating material. Since the coating film can be made uniform in thickness and can be made thin entirely, printability of solder paste is enhanced and defective print can be reduced. Furthermore, mountability of the electronic device having solder bumps, e.g. BGA, CSP, and the like, is enhanced because planarity of the device mounting face is maintained and defective mounting can be reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a printed circuit board suitable for mounting electronic parts with solder bumps.

[0002]

2. Description of the Related Art In order to further reduce the size, weight and performance of electronic devices, it is important to improve the mounting density of components on a mounting board. In recent years, in order to meet the demand for higher component density in such electronic devices, BGA (Ball Grid Array), CSP (Chip Size)
There has been provided a technology for forming an electronic unit by surface mounting electronic components of a type in which a large number of electrodes are arranged on a mounting surface, such as a package, on a printed circuit board.

In the above-described BGA and CSP, a large number of solder balls are arranged in a grid pattern on a mounting surface (bottom surface) of a square or rectangular package at a constant pitch (for example, 1.27 mm).
(Pitch) to form a hemispherical or spherical electrode (solder bump). Therefore, on a printed circuit board on which this kind of electronic component is mounted, mounting pads are provided at positions facing the respective solder bumps.

FIG. 3 shows an arrangement of land patterns on a component mounting surface of a conventional printed circuit board on which the above-mentioned BGA or CSP is mounted. In FIG. 3, circles arranged in a lattice shape indicated by reference numeral 2 are lands (BGA, C
SP mounting pad), and double circles indicated by reference numeral 3 are through-hole lands for conduction between circuits (ie, via holes).
It is. Thus, the printed circuit board 1 corresponding to the high-density mounting
In this case, conductor patterns such as mounting pads 2, through-hole lands 3, and wiring patterns (not shown, the wiring patterns also pass between the lands) are arranged with a strict wiring density while being adjacent to each other. ing. Note that a solder resist film is provided on the entire surface of both sides of the printed circuit board 1 for insulation protection except for electrical connection portions (portions to be soldered).

By the way, in such a state where a large number of conductor patterns are densely packed, if the through hole land 3 is not insulated and the conductor portion is exposed, especially in FIG. In a portion where the mounting pad 2 and the through-hole land 3 are adjacent to or close to each other, such as between or around the portion, there is a very high possibility that the conductors will be short-circuited by a solder bridge at the time of component mounting (during reflow soldering). High, which may cause failure.

In order to prevent a short circuit due to a solder bridge,
In addition to the insulating coating process using a solder resist, printing ink, or the like that is usually performed in a printed circuit board manufacturing process, it is effective to perform insulating coating on all exposed patterns (through-hole lands 3) adjacent to or adjacent to the mounting pad. Japanese Patent Publication No. 54-41102,
JP-A-6-260743 is disclosed.

[0007]

According to these disclosed techniques, as shown in the cross-sectional view of the printed circuit board 1 shown in FIG. Furthermore, since the structure is partially covered with the insulating material 4 such as a solder resist or a marking ink (silk), the thickness of the coating film varies, and the height difference significantly deteriorates the printability and component mountability of the solder paste. Was bad. In FIG. 4, reference numeral 5 denotes a coating film made of a solder resist or the like formed in the above-described ordinary printed circuit board manufacturing process.

Conventionally, such coating treatment has been performed before the conductor surface treatment (for example, Ni / Au plating treatment). (Conventionally, the conductor surface treatment has been performed in the final step of manufacturing a printed circuit board.) ) Even if the land part is covered, even if the insulation material at the time of covering processing is clogged inside the through-hole, the through-hole conductor will be corroded and disconnected by the plating solution from the subsequent surface treatment, which will affect the reliability of the printed circuit board. There was a problem of coming.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems when mounting electronic components with solder bumps such as BGA and CSP. It is an object of the present invention to provide a printed circuit board that improves the reliability of a component module.

[0010]

That is, according to the first aspect of the present invention, in a printed circuit board on which an electronic component with solder bumps is mounted, an exposed pattern close to a mounting pad to which the solder bump of the electronic component is connected is formed. It is characterized by being covered by an insulating material at one time.

Further, according to the invention described in claim 2, the portion covering the exposed pattern is formed between the arrangement of the mounting pads.
And the whole area around the mounting pad.

Further, the invention according to claim 3 is characterized in that the insulating coating of the exposed pattern is performed after a conductor surface treatment step.

The invention according to claims 4 to 6 is characterized in that a marking ink (silk), a solder resist, or an insulating film is used as a coating material.

Further, the invention according to claim 7 is characterized in that the electronic component is a BGA or a CSP connected to a mounting pad through a solder bump.

According to the first and second aspects, in addition to the original effect of preventing a short circuit between conductors due to the solder bridge, the thickness of the coating film can be made uniform and thin. The BG according to claim 7, wherein the printability of the solder paste on the mounting pad is improved, printing defects can be reduced, and the flatness of the component mounting surface is maintained.
A, The mountability of the CSP is also improved, and mounting defects can be reduced.
According to the third aspect, the corrosion and disconnection of the through-hole conductor due to the plating solution during the conductor surface treatment are prevented, and the reliability (conductivity) of the through-hole is improved, so that the reliability of the electronic component module is improved. Connect.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. FIG. 1 is a view showing an arrangement state of land patterns on a printed circuit board according to the present invention, and FIG. 2 is a sectional view thereof. To simplify the description, the same reference numerals are used in the following description for portions common to the related art.

The printed circuit board 1 shown in FIG. 1 has exactly the same land arrangement as that of the conventional printed circuit board shown in FIG.
A, mounting pads for CSP), and double circles indicated by reference numeral 3 are through-hole lands (via holes).

Here, as in the case of the land arrangement in the arrangement of the mounting pads 2 and the periphery of the mounting pad 2, the insulation coating processing in the part where the mounting pad 2 and the through-hole land 3 are adjacent to or close to each other is as follows. As shown in FIG. 3, the through hole lands 3 existing in the portion are conventionally individually covered as shown in FIG. 3, but in the present embodiment, as shown in FIG. And divided into a region a1 (between the arrangement of the mounting pads 2) and a region a2 (a peripheral portion of the mounting pad 2).
Is different from the first embodiment in that the entire structure is insulated.
Insulation materials include marking ink (silk),
In addition to the solder resist, an insulating film or the like can be used.

This solves the problem that the thickness of the coating film becomes non-uniform as in the conventional structure, and as shown in FIG. 2, the thickness of the coating film is made uniform and thin as a whole. Will be able to

Incidentally, the following table shows a comparison between the thickness of the coating film of the conventional structure and the thickness of the coating film of the structure according to the present invention.
The thickness data was measured at 11 arbitrary via holes (NO1 to 11) on the printed circuit board 1, and the coating was silk-screened.

Conventional coating thickness (μm) Coating thickness (μm) of the present invention NO1 33.0 22.0 NO2 36.0 19.0 NO3 34.0 22.0 NO4 38.0 20.0 NO5 40.0 20.0 NO6 38.0 23.0 NO7 28.0 22.0 NO8 31.0 22.0 NO9 30.0 20.0 NO10 32.0 20.0 NO11 32.0 19.0

According to the data, the thickness average was 33.8 μm and the thickness variation was 3.6 μm (standard deviation) in the conventional case, whereas the thickness average was 20.8 μm in the case of the present invention.
m, and the thickness variation was 1.3 μm.

As described above, according to the present invention, since the thickness of the coating film can be made uniform and thin as a whole, not only short-circuiting between conductors due to the solder bridge can be prevented, but also printing of solder paste at the time of component mounting. (Micro solder printing) can be facilitated and printing defects can be reduced. In addition, if the coating film is uniformly thin, the height difference from the mounting pad arrangement portion can be reduced, and the flatness of the component mounting surface is maintained,
Mounting defects can be reduced without hindering the mounting of electronic components having a large number of solder bumps such as BGA and CSP. That is, in the present invention, since the thickness of the coating film can always be made smaller than the height of the solder bump of the component, the bump and the pad are in close contact with each other, and no floating of the component occurs, so that the solder connection is ensured.

Further, in the present invention, unlike the conventional case, the insulating coating treatment of the through-hole land 3 is performed after the conductor surface is finished with Ni / Au or the like. By doing so, the plating solution during the surface treatment does not remain inside the through-hole, and the corrosion and disconnection of the through-hole conductor due to the residual plating solution as in the prior art can be prevented. ) Can be improved.

In this embodiment, the BGA and the CSP have been described as electronic components mounted on a printed circuit board. However, the present invention is not limited to these, and it is effective for mounting all semiconductor components having solder bumps. Of course.

[0026]

As described above, according to the present invention,
The exposed pattern near / adjacent to the mounting pad is covered with the insulating material at a time, so the short circuit between conductors due to solder bridges can be prevented. Since the solder paste can be made thinner, the printability of the solder paste is improved, and printing defects can be reduced. Also, since the flatness of the component mounting surface is maintained, B
The mountability of electronic components with solder bumps such as GA and CSP is also improved, and mounting defects can be reduced.

Further, by performing the insulating coating treatment after the conductor surface treatment step, corrosion and disconnection of the through-hole conductor due to the plating solution can be prevented, the reliability of the through-hole is improved, and the reliability of the electronic component module is improved. Can contribute.

[Brief description of the drawings]

FIG. 1 is a diagram showing an arrangement state of a land pattern on a component mounting surface of a printed circuit board according to the present invention.

FIG. 2 is a cross-sectional view of the printed circuit board shown in FIG.

FIG. 3 is a diagram showing an arrangement state of a land pattern on a component mounting surface of a conventional printed circuit board.

FIG. 4 is a sectional view of the printed circuit board shown in FIG. 3;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Printed circuit board 2 Mounting pad 3 Exposed pattern (through-hole land) 4 Insulation material

Claims (7)

[Claims] 1. A printed circuit board on which an electronic component with solder bumps is mounted, wherein an exposed pattern close to a mounting pad to which the solder bump of the electronic component is connected is collectively covered with an insulating material. substrate. 2. The printed circuit board according to claim 1, wherein the portion covering the exposed pattern is between the arrangement of the mounting pads and the whole area around the mounting pads. 3. The method according to claim 1, wherein the insulating coating of the exposed pattern is performed after a conductor surface treatment step.
A printed circuit board according to claim 2. 4. The printed circuit board according to claim 1, wherein a marking ink is used as the coating material. 5. The printed circuit board according to claim 1, wherein a solder resist is used as the coating material. 6. The printed circuit board according to claim 1, wherein an insulating film is used as the coating material. 7. The printed circuit board according to claim 1, wherein the electronic component is a BGA or a CSP connected to a mounting pad through a solder bump.