JPH0951156A - Formation of solder resist in printed wiring board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the forming method of the solder resist in a printed wiring board, which can positively prevent the migration caused by the residue of ions on the back covered solder resist. SOLUTION: Resin 7 for forming a solder resist is applied on a substrate 3, on both surfaces of which conductor patterns 6 are formed. The applied resin 7 is exposed, developed and hardened, and the solder resist 2 is formed. At this time, ion removing processing for removing the residue of ions in the surface layer of the resin 7 is performed after the developing process.

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 printed wiring board.

[0002]

2. Description of the Related Art Conventionally, as one method for protecting a conductor pattern of a printed wiring board from moisture and the like, it is usually common to coat the conductor pattern with a solder resist. Here, a general procedure for forming the solder resist will be briefly described.

First, a substrate having conductor patterns formed on both sides is prepared, and a photosensitive resin for forming a solder resist is applied to both sides of the substrate. Next, the applied resin is partially exposed using an exposure device. Then, the exposed resin is developed with a developing solution such as an aqueous solution of sodium carbonate, and then cured by heat or light. As a result, a desired solder resist that covers the conductor pattern can be obtained.

[0004]

However, when the substrate forming the printed wiring board is thin, if the exposure step is performed after the resin double-sided coating step, light will inevitably pass through to the opposite side surface. In this case, the resin on the opposite side is also polymerized to some extent, and so-called backside fogging of the solder resist occurs. In addition, backfogging is a phenomenon that occurs when light is applied from the backside, so photocuring is not sufficient, so that Na ⁺ in the developer is
Ions tend to remain. Then, the remaining Na ⁺ ions cause migration between the conductor patterns, which deteriorates the insulation reliability of the printed wiring board.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a printed wiring board capable of reliably preventing migration due to residual ions on the back-covered solder resist. It is to provide a method for forming a solder resist.

[0006]

In order to solve the above-mentioned problems, the invention according to claim 1 comprises a step of forming a resin layer for forming a solder resist on a substrate having conductor patterns formed on both sides, Exposing and developing the formed resin layer,
In a method for forming a solder resist in a printed wiring board, which comprises a step of forming a desired pattern by curing, an ion removal treatment for removing an ion residue on the surface layer of the resin is performed after the development. The method of forming a solder resist on a printed wiring board is described below.

According to a second aspect of the present invention, in the first aspect, the ion removing process is performed before the curing. According to the invention described in claim 3, in claim 1 or 2, the ion removal treatment is a neutralization treatment using an acidic aqueous solution.

According to a fourth aspect of the present invention, in the first or second aspect, the developing solution is a sodium carbonate aqueous solution, and the ion removing treatment is a neutralizing treatment using a hydrochloric acid aqueous solution.

According to a fifth aspect of the present invention, in the fourth aspect, the treatment concentration of the hydrochloric acid aqueous solution is 3% by weight to 6% by weight. Hereinafter, the "action" of the present invention will be described.

According to the first to fifth aspects of the present invention, the ions removed from the resin surface layer are removed by the ion removal treatment. According to the second aspect of the present invention, since the ion removal treatment is performed before the ions are firmly bound to the resin by being cured, the ions are removed more reliably.

According to the third aspect of the present invention, since the ion removing treatment is a neutralizing treatment, the ions are more surely removed as compared with, for example, a rinse treatment using a neutral liquid.
According to the invention as set forth in claim 5, the neutralization reaction can be achieved without excess or deficiency within this range, so that ions can be reliably removed. That is, if the treatment concentration is too low, Na ⁺ ions will remain in the back cover.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of a method for forming a solder resist 2 in a printed wiring board 1 embodying the present invention will be described in detail below with reference to FIGS.

First, as shown in FIG. 1A, a copper clad laminate 5 having copper foils 4 attached to both surfaces of an insulating substrate 3 is prepared as a starting material for the printed wiring board 1. Next, as shown in FIG. 1B, the copper foils 4 on both sides are etched according to a conventionally known subtractive process. As a result, the conductor pattern 6 having a predetermined shape is formed on both sides of the substrate 3.

Next, as shown in FIG. 1C, a photosensitive resin 7 for forming a solder resist is entirely applied to both surfaces of the substrate 3. The photosensitive resin 7 for forming the solder resist used in this embodiment is water-soluble. Next, the applied resin 7 is irradiated with ultraviolet rays using a double-sided simultaneous exposure machine to partially expose the resin 7. At this time, polymerization occurs in the resin 7 in the portion irradiated with light.

Next, the exposed resin 7 is developed with a developer containing ions to remove the resin 7 in the unexposed portion from the substrate 3. The developer as used herein is a low-concentration alkaline aqueous solution, and specifically, for example, 1 wt% to 3 wt% sodium carbonate (Na ₂ CO ₃ ) aqueous solution, potassium carbonate (K
₂ CO ₃ ) aqueous solution, sodium phosphate (Na ₃ PO ₃ ).
An aqueous solution, a potassium phosphate (K ₃ PO ₃ ) aqueous solution, a sodium acetate (CH ₃ COONa) aqueous solution, a sodium nitrate (NaNO ₃ ) aqueous solution, and the like. That is, this developer contains Na ⁺ ions (or K ⁺ ions).

FIG. 1D shows the state of the substrate 3 after the exposure process. The lower surface side of the substrate 3 is covered with the polymerized resin 7. Further, on the upper surface side of the substrate 3, what is called a back covering portion U1 is generated by the polymerization of the resin 7 by the action of the light transmitted from the lower surface side. The back cover U1 is thinly formed in the space between the conductor patterns 6. As shown in FIG. 2, the surface layer of the back cover U1 has a functional group that is not sufficiently crosslinked, and Na ⁺ ions or the like are bonded to the functional group.

Next, an ion removing process for removing ion residues on the surface layer of the resin 7 is carried out. In the present embodiment, since the ions to be removed are Na ⁺ ions, the ion removal process is a neutralization process using an acidic aqueous solution. This is because the neutralization treatment makes it possible to remove the ions more reliably than with a rinse or the like using a simple neutral liquid. Specifically, a hydrochloric acid aqueous solution is used as the acidic aqueous solution, and the substrate 3 is dipped in a tank filled with the hydrochloric acid aqueous solution for a predetermined time. The reason for selecting hydrochloric acid is that it seems to be most suitable for removing Na ⁺ . Here, the treatment concentration of the hydrochloric acid aqueous solution is preferably 3% by weight to 6% by weight. This is because if it is within such a range, it is possible to achieve a neutralization reaction that is sufficient and sufficient, so that reliable ion removal can be achieved. If this concentration is too low, Na ⁺ may be added to the back cover U1.
Ions will remain. On the other hand, if the concentration is too high, there are disadvantages that other parts of the printed wiring board 1 are adversely affected, and it becomes difficult to control the processing time and the processing temperature.

The hydrochloric acid aqueous solution is at room temperature for 0.5 minutes to 1
It is preferably treated for minutes. If the temperature of the aqueous hydrochloric acid solution is too low, the processing speed becomes slower, so that it is necessary to set the processing time longer and the productivity becomes worse. On the contrary, if this temperature is too high, it may adversely affect other parts of the printed wiring board 1. If the treatment time of the hydrochloric acid aqueous solution is too short, Na ⁺ ions may not be completely removed depending on the conditions. On the contrary, if the treatment time is too long, the Na ⁺ ions are completely removed, but the productivity is deteriorated.

When the above processing is performed, as shown in FIG.
And Na from the surface of the back cover U1 ⁺Ions are surely removed
Left. Finally, to cure the developed resin 7.
As shown in FIG. 1 (e), the solder resist
You can get the second. Printed wiring board 1 is above
Completed after a while.

In the method for forming the solder resist 2 in the present embodiment, Na ⁺ ions remaining on the surface layer of the resin 7 are removed by the ion removal treatment. Therefore, migration can be reliably prevented, and the printed wiring board 1 having excellent insulation reliability can be obtained. In particular, according to the present embodiment, since the ion removal treatment is performed before the Na ⁺ ions are firmly bound to the resin 7 through the curing treatment, there is an advantage that the Na ⁺ ions are more reliably removed. is there.

[0021]

EXAMPLE 1% by weight to 2% by weight of charcoal was used as a developing solution.
For ion removal treatment when using sodium acid aqueous solution
Table 1 shows the results of a comparative test. Test area 1
10 is an example, and test plots 11 and 12 correspond to them.
This is a comparative example. That is, in the test area 12, just water is used.
The ion removal process. In addition, in this test
Performs EPMA on the back cover U1 after processing,
Na per unit area ⁺The amount of attached ions was measured. So
Then, this measured value was considered in the evaluation. Also sol
Regarding whether or not the dar resist 2 is eroded
Was visually inspected.

[0022]

[Table 1] The present invention can be modified as follows, for example. (1) When the alkaline developer as in the above embodiment is used, an aqueous solution of, for example, sulfuric acid, nitric acid, carbonic acid, phosphoric acid, boric acid, acetic acid or the like can be selected in addition to the hydrochloric acid aqueous solution. Is.

(2) The ion removing treatment is not limited to the dipping treatment as in the above embodiment, and may be, for example, a spraying treatment. (3) The ion removal treatment may be performed by a method other than the neutralization treatment. For example, it is conceivable to polish the back cover portion U1 itself from the substrate 3 by physical polishing or the like. However,
The neutralization treatment described above has the advantages that it is easier to carry out and that the obtained effect is higher.

Here, in addition to the technical ideas described in the claims, the technical ideas grasped by the above-described embodiments and other examples will be listed below together with their effects. (1) In Claims 4 and 5, the hydrochloric acid aqueous solution is treated at room temperature for 0.5 minutes to 1 minute. With this method, migration can be prevented more reliably.

The technical terms used in this specification are defined as follows. "Migration: A phenomenon in which the conductor metal dissolves due to an electrochemical reaction, causing a short circuit between the conductors and dielectric breakdown."

[0026]

As described above in detail, according to the inventions described in claims 1 to 5, the printed wiring can surely prevent the migration due to the residual of the ions on the back-covered solder resist. A method for forming a solder resist on a plate can be provided. Claims 2 and 3
According to the invention described in (3), the migration can be more surely prevented. According to the invention described in claim 5, migration can be more surely prevented.

[Brief description of drawings]

1A to 1E are partially enlarged cross-sectional views for explaining a method for forming a solder resist in a printed wiring board according to an embodiment.

FIG. 2 is an enlarged schematic sectional view of a back cover portion.

FIG. 3 is an enlarged schematic sectional view of a back cover portion.

[Explanation of symbols]

1 ... Printed wiring board, 2 ... Solder resist, 3 ... Substrate, 6 ... Conductor pattern, 7 ... Resin for forming solder resist.

Claims (5)

[Claims] 1. A step of forming a resin layer for forming a solder resist on a substrate having conductor patterns formed on both sides thereof, and a desired pattern is formed by exposing, developing and curing the formed resin layer. A method of forming a solder resist in a printed wiring board, the method comprising the steps of: performing an ion removal treatment for removing ion residues on the surface layer of the resin after the development. Method. 2. The method for forming a solder resist in a printed wiring board according to claim 1, wherein the ion removal treatment is performed before the curing. 3. The method for forming a solder resist in a printed wiring board according to claim 1, wherein the ion removal treatment is a neutralization treatment using an acidic aqueous solution. 4. The method for forming a solder resist in a printed wiring board according to claim 1, wherein the developing solution is a sodium carbonate aqueous solution, and the ion removing treatment is a neutralizing treatment using a hydrochloric acid aqueous solution. 5. The treatment concentration of the hydrochloric acid aqueous solution is 3% by weight to 6%.
The method for forming a solder resist in a printed wiring board according to claim 4, wherein the amount is% by weight.