JP3037316B1 - Solder resist forming method - Google Patents

Abstract

An object of the present invention is to enable laser processing under low energy and under the same conditions, without generating a solder resist residue burnt by a laser on the bottom of a micro via, high productivity of laser processing, stable accuracy and quality. Is provided. In contrast to a configuration in which solder resist openings are formed in CSP pads (2a, 2b), after exposing a solder resist (4) via a photomask (5) as shown in FIG. As shown in e), a solder resist opening 7b larger than the micro via diameter is obtained. FIG.
As shown in FIG.
As shown in (g), a pad-shaped solder resist opening 9 is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a solder resist on a build-up board on which a normal surface-mounted component and a high-precision mounted component such as a CSP (chip size package) are mounted. In particular, the present invention belongs to a solder resist forming method capable of removing a solder resist residue by laser processing under low energy and the same condition regardless of the presence or absence of the micro via of the CSP pad.

[0002]

2. Description of the Related Art Conventionally, a method of forming a solder resist is described in US Pat.
Used in high-density wiring design on boards on which high-density components such as SPs are mounted. Highly accurate pads and circuit positions are used to completely expose pads from solder resist and cover adjacent circuits with solder resist. High solder resist position accuracy is required. Also, CS
As the number of rows of P pads increases, the number of wirings further increases,
In many cases, the wiring cannot be pulled out by one layer, and the wiring is dropped to the lower layer through a micro via using a build-up substrate, and the wiring is drawn out in two layers.

As a method of forming a solder resist with high positional accuracy, the solder resist is baked and vaporized by laser processing instead of the conventional method of forming a solder resist opening by exposure and development using a mask film. A technique of forming a portion is employed.

[0004] Japanese Patent Application Laid-Open No. Hei 4-267582 and Japanese Patent Publication No. 2615120 disclose a method of accurately forming a solder resist opening by laser processing.
Japanese Patent Application Laid-Open No. 4-267852 discloses that a solder resist is formed on the entire surface of a substrate having pads for mounting high-precision parts and pads for mounting normal parts, A technique is described in which a solder resist is removed by exposure and development processing, and a solder resist on a pad for mounting a high-precision component is removed by laser light irradiation. In addition, a technique of irradiating a laser beam onto a desired pad using a mask is exemplified. In Japanese Patent Publication No. 2615120, in order to remove a resist on a conductor pattern, a stencil provided with a plurality of types of transmission ports is arranged in an irradiation optical path of a pulsed laser,
A technique is described in which the shape of a laser irradiation spot is formed by a selected transmission opening of a stencil.

According to Japanese Patent Application Laid-Open No. 9-237958, a solder resist is formed on a pad in advance, a solder resist is formed thereon, and the entire substrate is irradiated with a laser beam to remove the solder resist. There is described a technique for preventing sticking of a baked solder resist residue and eliminating a post-process for removing the solder resist residue.

[0006]

However, the prior art has the following problems. JP-A-4-267
In the method of forming an opening by baking and evaporating a solder resist by laser processing as disclosed in Japanese Patent No. 582, Patent Publication No. 2615120, etc., the solder resist baked by laser irradiation adheres to the pad surface. For this reason, after laser processing, a post-process consisting of swelling, etching, and neutralization is performed to remove the baked solder resist residue. Cleaning of the solder resist is extremely difficult, and often cannot be completely removed, causing a connection reliability problem at the time of mounting the CSP.

The energy of laser irradiation necessary for forming the solder resist opening has a correlation with the thickness of the solder resist. An experiment was performed on the thickness of the solder resist and the energy of the laser irradiation. In order to form a solder resist opening with a carbon dioxide laser having a spot diameter of 0.3 mm, the solder resist thickness was 3 mm.
16 mJ at 5 μm, 22-28 mJ at 70 μm, 1
It has been found that an energy of 32 to 44 mJ is required at 05 μm. In the case of an average solder resist application, the thickness of the solder resist on a pad having no micro via is only 20 to 30 μm. On the contrary,
In a pad having a micro via connection seen in a build-up substrate, the solder resist flows into the pad after the solder resist is applied, so that the micro via portion has a thickness of 80 to 110 μm. Therefore, when there is a micro via, a solder resist opening cannot be formed without irradiating a laser with an energy amount of two to three times the normal amount.

[0008] The laser processing machine requires a large investment because it has a large investment. However, for the above reasons, the formation of a solder resist for a CSP pad having micro vias has a disadvantage that the laser processing time is long and the productivity is reduced. is there.

Further, from the experimental results on the energy of the laser irradiation and the opening shape of the solder resist, the opening shape of the solder resist is uniquely defined by the mask shape placed in the laser path. It has been found that the shape of the opening tends to become larger under the influence of the laser reflected on the pad. When an opening is formed in a 35 μm-thick solder resist with a carbon dioxide gas laser having a spot diameter of 0.3 mm, the energy amount is 1
0.294mm at 6mJ, 0.316m at 28mJ
It has been found that at m and 44 mJ, it is 0.366 mm. When high-energy laser conditions are applied to open the solder resist inside the microvia, the CS with no microvia in the same CSP pad group
The opening of the P pad becomes excessively large, and there is a disadvantage that an adjacent circuit is exposed.

The present invention has been made in view of the above problems, and has as its object to be able to perform laser processing under low energy and the same condition regardless of the presence or absence of a micro via of a CSP pad. An object of the present invention is to provide a solder resist forming method which does not generate a solder resist residue burnt by a laser on the bottom, has high laser processing productivity, and can obtain stable accuracy and quality.

[0011]

An image pickup method according to claim 1.
Has normal surface mount component pads and micro vias
Solder register for build-up board with CSP pad
In the strike forming method, a solder resist material is applied
Solder at the center of the CSP pad of the build-up substrate
-Remove the resist and apply it to the periphery of the CSP pad surface
Leaving only the solder resist, solder resist opening
Exposure / development process for providing a section and the CSP pad table
Processing solder resist remaining only on the periphery of the surface
The solder resist opening of the CSP pad
And left only on the periphery of the CSP pad surface
Laser processing to remove solder resist residue
Solder resist forming method characterized by performing
I do. The imaging method according to claim 2, wherein the laser processing step
Is the solder resist provided in the exposure / development process.
After applying solder plating to the strike opening,
The method for forming a solder resist according to claim 1, wherein
Exist. The imaging method according to claim 3, wherein the exposure and development process is performed.
In the process, the diameter is larger than the micro via diameter of the CSP pad.
Open solder resist smaller than the CSP pad
2. The solder according to claim 1, wherein a mouth is provided.
A method for forming a resist. An imaging method according to claim 4.
Means that the photomask and the substrate
Larger than the microvia diameter
Claims characterized by providing a solder resist opening
Item 1 is a solder resist forming method according to Item 1. Claim
5. The imaging method according to item 5, wherein in the exposure / development processing step,
If the position error between the photomask and the substrate is
It is characterized by providing a smaller solder resist opening
The method for forming a solder resist according to claim 1,
You.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The solder resist forming method of the present invention relates to a method of forming a solder resist for a fine pad such as a chip size package (hereinafter referred to as a CSP) connected by micro vias in a pad such as a build-up substrate by a photo method in advance. After the solder resist is opened in a shape larger than the micro via diameter, the solder resist is again opened in a pad shape by laser processing.

Referring to FIG. 1, the method of forming a solder resist according to the present invention is different from the method of forming a solder resist opening in CSP pads 2a and 2b through a photomask 5 as shown in FIG. After exposing the solder resist 4, the solder resist 4 is developed to obtain a solder resist opening 7b larger than the micro via diameter as shown in FIG. Next, as shown in FIG. 1 (f), a carbon dioxide laser 8 is irradiated to obtain a pad-shaped solder resist opening 9 as shown in FIG. 1 (g).

In the step of exposing and developing the solder resist through the photomask, the step of exposing and developing the solder resist flowing into the micro via of the CSP pad 2a is performed.
Remove the solder resist at the center of the SP pad and remove the CSP
It serves to leave the solder resist only on the periphery of the pad surface.

In the next laser processing step, only the solder resist remaining only on the peripheral portion of the CSP pad surface is processed, the solder resist opening is shaped, and the solder resist scum is removed. Regardless of the presence or absence, a laser with low energy and the same conditions can be used.

Hereinafter, an embodiment of a method for forming a solder resist according to the present invention will be described in detail with reference to the drawings.

(First Embodiment) FIGS. 1 (a) to 1 (h)
It is a top view and a sectional view explaining an embodiment of a solder resist formation method of the present invention. FIG. 1A is a plan view of a build-up wiring board completed up to circuit formation. Normal surface mount component pads 1 and CSP pads 2a and 2b are mixed on the surface of the substrate. The CSP pad 2a has a micro via with a depth of 40 to 100 μm, and is connected to the lower land 3. 1 (b) to 1 (h) correspond to FIG.
The AA 'cross section of FIG. less than,
The method of forming the solder resist according to the present embodiment is described as AA
'A cross-sectional view will be used.

A photosensitive solder resist 4 (PSR-4000 manufactured by Taiyo Ink Mfg. Co., Ltd.) is applied to the entire surface of the build-up substrate on which the circuit formation of FIG. Apply ² and
It is dried in a hot air circulating drying oven at 80 to 90 ° C. for 20 to 60 minutes to obtain a solder resist dry film of 15 to 70 μm as shown in FIG.

Preferably, 90 to 110 g / m ² per side.
Is applied and dried to obtain a solder resist film of 25 to 35 μm. Further, the photosensitive solder resist material is not limited to the above, and a commonly used photosensitive solder resist material can be applied. The method for applying the photosensitive solder resist is not limited to the curtain coating method. For example, in the case of a liquid photosensitive solder resist, a commonly used coating method such as a screen printing method, a spray coating method, and a roll coating method can be applied. Further, the present invention is also applicable when laminating and coating a dry film type photosensitive solder resist.

Next, as shown in FIG. 1 (d), ultraviolet rays 6 having a wavelength of 350 to 420 nm are irradiated with a UV light having a wavelength of 350 to 420 nm through a photomask 5 having a predetermined pattern using a contact exposure device.
The solder resist film is exposed by irradiating 000 mJ / cm ² .

In the present embodiment, a negative mask film is used because the photosensitive solder resist is a negative type. However, when the photosensitive solder resist is a positive type, the present invention can be applied using a positive mask film. When the type of the photosensitive solder resist is different, the irradiation wavelength and the amount of exposure energy may be set to conditions suitable for the photosensitive performance of the photosensitive solder resist to be used.

Next, the unexposed portion is dissolved and removed with a developing solution consisting of a 0.5 to 2 wt% aqueous solution of sodium carbonate at 25 to 35 ° C., as shown in FIG. A solder resist opening 7a for the CSP pad and a solder resist opening 7b for the CSP pad.
An opening is formed in the ordinary surface mount component pad 1 in a similar shape larger than the outer shape of the pad. CSP pads 2a, 2b
The opening is larger than the micro via and smaller than the outer shape of the pad.

The developing solution is not limited to the substances described in the present embodiment, but may be any developing solution suitable for the photosensitive solder resist to be used. Depending on the type of the photosensitive solder resist, an optimal developing solution such as an organic solvent or another aqueous alkaline solution, or a mixture of an aqueous alkaline solution and an organic solvent may be used.

Here, a description will be given of a solder resist opening of a CSP pad 2a having a micro via in a case where two circuits are wired between pads using a CSP pad having a pitch of 0.5 mm, with reference to FIG. 2A and 2B are a plan view and a cross-sectional view illustrating a CSP pad and a solder resist opening according to the embodiment of the present invention.

FIG. 2A shows a CSP having micro vias.
FIG. 2B is a cross-sectional view taken along line AA ′ of the pad as viewed from above. Micro via (diameter D1 = 0.125m
m) formed CSP pad (outer diameter = 0.275m)
m) is covered with the solder resist 4. At this time, the solder resist opening 7b has a diameter D2 = 0.200 mm.
Circle.

The reason for the above design values is that, since the positional accuracy for aligning the substrate and the mask film is ± 0.025 mm, even when mismatching occurs, it is necessary to completely remove the solder resist inside the microvia. It is also possible to prevent the circuit adjacent to the pad from being exposed from the solder resist opening. In the case of D2 <0.175 mm, when the mismatch is large, the solder resist inside the microvia is exposed, and there is a risk that the solder resist inside the microvia cannot be completely removed in the developing process.
When D2> 0.225 mm, the solder resist on the circuit adjacent to the pad is not exposed, and there is a risk that copper in the adjacent circuit is exposed.

FIG. 3 shows a CSP according to an embodiment of the present invention.
It is a top view which illustrates a pad. CSP pad shape,
Further, the shape of the solder resist opening is not limited to a circle as shown in FIG. 2, but can be applied to various shapes including the shape illustrated in FIG. Regardless of the shape, the solder resist opening must be designed so that the micro via portion in the pad is entirely exposed and the copper of the adjacent circuit is not exposed on the pad.

As shown in FIG. 1 (f), the CSP pad is irradiated with a carbon dioxide gas laser
By baking and evaporating the solder resist remaining around b, the solder resist opening 9 is formed.

The laser processing conditions include the diameter of the CSP pad,
Optimum conditions vary depending on the type of solder resist, coating method, thickness, and degree of curing.
In case of P, spot diameter φ0.275 ~ 0.300m
It is preferable to irradiate 1 to 2 pulses of the carbon dioxide laser 8 of 5 m at 5 to 20 mJ.

As shown in FIG. 1 (g), the solder resist scum 10 burned by the laser is adhered to the periphery of the pad surface of the CSP pads 2a and 2b opened by the laser.

Further, Shipley Far East Co., Ltd.
MLB211 is 20 vol%, Cupposit Z is 1
Immersion in a swelling bath of 60 to 85 ° C. consisting of 0 vol% for 1 to 5 minutes.
B was immersed for 2 to 10 minutes in an etching bath at 55 to 75 ° C. containing 15 vol%, and finally MLB216-2 was 20
The solder resist scum 10 is cleaned by immersing it in a neutralization bath of 35% to 55 ° C. of 30% by volume for 2 to 10 minutes to obtain a clean CS as shown in FIG.
Obtain a P pad.

In the method for forming a solder resist according to the present embodiment, the formation of the solder resist opening is performed in two steps, ie, an exposure / development step using a mask film and a laser processing step. In the CSP pad, since the solder resist inside the micro via has been removed in advance in the development process, the solder resist removal in laser processing is performed on the solder resist remaining only in the peripheral part of the CSP pad regardless of the presence or absence of the micro via. And the solder resist inside the micro via is not required.

Therefore, laser irradiation with excessive energy for removing the solder resist in the micro via is not required, and all CSs are irrespective of the presence or absence of the micro via.
The same laser processing conditions can be applied to the P pad.
This facilitates management and increases the laser processing speed. Further, since there is no residue of the solder resist burned by the laser inside the micro via, an effect that the reliability of solder connection at the time of component mounting is high is brought about.

(Second Embodiment) Another embodiment of the solder resist forming method of the present invention will be described with reference to FIG.

FIGS. 4A to 4I are a plan view and a sectional view for explaining another embodiment of the solder resist forming method of the present invention. FIG. 4A is a plan view of a printed wiring board which has been completed up to circuit formation as in the first embodiment, and FIGS. 4B to 4I are cross-sectional views taken along the line AA ′ of FIG. It is shown in the order of steps.

FIGS. 4 (b) to 4 (e) show the above-described first embodiment.
Processing is performed in the same manner as in the embodiment. Next, as shown in FIG. 4F, after the solder paste 11 is supplied to the entire surface of the CSP pad group, the solder is melted and soaked under the solder resist as shown in FIG. Cover the entire part with solder.

The method of supplying the solder is to use a metal mask having a thickness of 0.2 mm manufactured by the additive method.
The solder paste NSP-95 manufactured by Tamura Corporation was printed. After printing solder, peak temperature 220-240 ° C
Was heated in a nitrogen reflow furnace set to the above to melt the solder.

Further, as shown in FIG. 4H, the carbon dioxide laser 8 is formed on the CSP pad in the same manner as in the first embodiment.
To bake and evaporate the solder resist. At this time, the solder is re-melted at the same time, and the burned-in solder resist emerges on the solder. After cooling, the solder resist protruding from the solder surface is washed, and a printed wiring board as shown in FIG. 4 (i) is obtained.

The method for forming a solder resist according to the present embodiment has the same effects as the first embodiment. Further, since the solder resist baked by the laser processing does not adhere to the copper pad, the swelling, roughening, and neutralizing steps are not required.

In the present embodiment, the present invention is not limited to this, and can be applied to the formation of a resist for a wiring board suitable for applying the present invention.

Further, the number, position, shape, etc. of the above-mentioned constituent members, such as CSP pads, ordinary surface-mounted component pads, wiring, etc., are not limited to the above-described embodiment, but are suitable numbers and positions for carrying out the invention. , Shape, etc.

In each of the drawings, the same components are denoted by the same reference numerals.

[0043]

Since the present invention is configured as described above, only the solder resist remaining on the peripheral portion of the CSP pad surface needs to be removed in the laser processing step. There is no need for high-energy laser processing conditions for removing the excessive solder resist that has flowed into the microvias, and low-energy laser processing conditions can be used, so that productivity is improved. Further, regardless of the presence or absence of the micro via of the CSP pad, the laser processing conditions can be set to the same conditions, so that quality control becomes easy. Further, there is obtained an effect that there is no fear that a solder resist residue burned by a laser is formed on the bottom of the micro via.

[Brief description of the drawings]

1A to 1H are a plan view and a cross-sectional view illustrating an embodiment of a solder resist forming method according to the present invention.

FIGS. 2A and 2B are a plan view and a cross-sectional view illustrating a CSP pad and a solder resist opening according to an embodiment of the present invention.

FIG. 3 is a plan view illustrating a CSP pad according to the embodiment of the present invention;

FIGS. 4A to 4I are a plan view and a cross-sectional view illustrating an embodiment of a solder resist forming method of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Surface mount component pad 2a CSP pad (with micro via) 2b CSP pad (without micro via) 3 Land 4 Solder resist 5 Photomask 6 Ultraviolet 7a Solder resist opening (surface mount component pad) 7b Solder resist opening (CSP pad) 8) Carbon dioxide gas laser 9 Solder resist opening 10 Solder resist scum 11 Solder paste

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H05K 3/28 H05K 3/46 H05K 3/00

Claims (5)

(57) [Claims] 1. A method of forming a solder resist for a build-up board provided with a normal surface mount component pad and a CSP pad having micro vias, wherein the build-up board coated with a solder resist material is provided.
Remove the solder resist at the center of the CSP pad
Apply solder resist only to the periphery of the CSP pad surface
An exposure / development process for providing a solder resist opening, and a solder remaining only in a peripheral portion of the CSP pad surface.
-Only the resist is processed to shape the solder resist opening of the CSP pad, and the periphery of the CSP pad is
Performing a laser processing step of removing a solder resist residue remaining on the side . 2. The method according to claim 1, wherein the laser processing step is performed after applying solder plating to a solder resist opening provided in the exposure / development processing step.
The method for forming a solder resist according to the above. 3. The method according to claim 1, wherein the exposing and developing process comprises
2. The method according to claim 1, further comprising providing a solder resist opening that is larger than the micro via diameter of the P pad and smaller than the CSP pad. 4. The solder resist formation according to claim 1, wherein in the exposure / development processing step, a solder resist opening is provided which is equal to or larger than a positional accuracy error between the photomask and the substrate and larger than a micro via diameter. Method. 5. The solder resist forming method according to claim 1, wherein, in the exposure / development process, a solder resist opening smaller than a pad is provided with an error of positional accuracy between the photomask and the substrate.