JP3405473B2 - Laser processing of heat-resistant resin - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser processing method for a heat resistant resin which is widely used in products such as printed wiring boards, multi-chip modules and ion flow printer heads which utilize laser processing.

[0002]

2. Description of the Related Art Mechanical processing methods, chemical etching processing methods, plasma processing methods, laser processing methods, etc. are used as processing methods for heat resistant resins such as polyimide resins and epoxy resins. Laser processing methods are used in required fields. Carbon dioxide laser, excimer laser and the like are mainly used as laser species for laser processing. Of these, the excimer laser is characterized in that it has a high oscillation wavelength in the ultraviolet region or vacuum ultraviolet region, short pulse, and high energy density per pulse. Therefore, the processing mechanism using this excimer laser is based on the process of "instantaneous light absorption, molecular bond cleavage due to photochemical reaction, volume increase due to cut fragments, and scattering", and is generally called ablation mechanism.
Therefore, in processing using an excimer laser, since it is not a thermal processing process, it has the characteristic that it does not cause thermal damage to the processing area and its surroundings and excels in the processed shape, but scattered fragments adhere to the periphery of the processed part. There is a problem that it becomes a processing residue. Depending on the processing residue, it is electrically conductive, and in the processing field where insulation between the holes is required such as ion flow printer head, it is necessary to remove the processing residue attached inside the holes. In addition, wiring boards and multi
When excimer laser processing is used for through-hole processing or blind through-hole processing in chips and modules, etc., the processing residue adhered inside and around the holes is ensured to ensure the reliability of electrical connection between layers. Removal is required. Conventionally, as a method of removing this processing residue, a method of utilizing plasma treatment is generally used.

[0003]

However, this plasma processing has some problems as described below. Firstly, the end point of the plasma processing cannot be strictly controlled because there are variations in the adhesion amount and adhesion state of the processing residue, the plasma energy in the plasma processing apparatus used for the processing, and the like. Therefore, in general, the treatment time is lengthened, but the resin in the portion where the processing residue is removed first is etched back. This is multi
When it is used for processing blinds, vias, holes, etc. of chips, modules, etc., it causes a significant decrease in connection reliability. Secondly, when the plasma treatment is performed, the surface temperature of the treated substrate rises, and the dimensional accuracy may be significantly reduced.
The present invention provides a laser processing method for a heat-resistant resin which can solve these problems and can remove the processing residue satisfactorily and which is widely used for drilling small diameter holes and the like.

[0004]

As a result of various experiments conducted by the present inventors, (a) a step of irradiating a heat-resistant resin with an excimer laser beam, (b) an alkaline solution of permanganate. in the process step of the manganese compound precipitated (c)
A treatment method including a step of removing by a neutralization treatment with a solution containing a reducing agent, wherein the steps (b) and (c) are performed at least twice is capable of removing the excimer laser processing residue and is a heat-resistant resin. It was found to be effective for laser processing of.

The permanganate is preferably an oxidizing agent such as sodium permanganate or potassium permanganate, and the alkaline agent is preferably sodium hydroxide, potassium hydroxide, potassium carbonate, sodium carbonate or the like. One or more permanganate and one alkaline agent may be appropriately combined and used. The optimum concentration is the type of processing solution,
The type of processed substrate processed, depending on the laser type, for example, when the residual removal after excimer laser processing is performed with a mixed aqueous solution of potassium permanganate and sodium hydroxide,
The concentration of the treatment liquid is 40-80 g of potassium permanganate.
/ L, sodium hydroxide 20-50g / l is good, preferably potassium permanganate 50-70g
/ L, sodium hydroxide 28-48g / l is good. The liquid temperature is preferably about 50 to 70 ° C. The processing time is preferably about 5 to 30 minutes. Treatment methods include dipping and spraying.

Further, the manganese compound deposited on the surface of the treated substrate by the above treatment is deposited. This manganese compound can be easily removed by a neutralization treatment with a solution containing a reducing agent. Examples of the reducing agent include hydroxylamine sulfate and hydrazine sulfate, and it is preferable to use a solution obtained by adding an acid to these. Examples of the acid include sulfuric acid, hydrochloric acid, nitric acid and the like. In some cases, a treatment method in which the reducing agent solution treatment and the acid treatment are performed separately, or after the solution treatment in which an acid is added to the reducing agent is further performed, an acid treatment is additionally performed is also effective.

It is also effective to carry out an organic solvent treatment such as immersion in an organic solvent prior to the alkaline solution immersion treatment of permanganate. Examples of the organic solvent include heterocyclic organic solvents such as N-methylpyrrolidone, amide compounds such as dimethylformamide, ketones such as hydrazine and acetone, alcohols such as isopropyl alcohol, and ethers such as ethylene glycol monobutyl ether. Is mentioned. These may be appropriately mixed and treated, or may be treated with several kinds of treatment liquids.
Moreover, it heats suitably at about 30-80 degreeC, and is used. 95% as the processing condition when the residue is removed after excimer laser processing and the processing is performed prior to the permanganate processing step.
When acetone is used, the liquid temperature is 20 ° C. and the treatment time is 5 to 10
When using 95% isopropyl alcohol,
Liquid temperature 20 ° C., processing time about 2 to 20 minutes, in the case of N-methylpyrrolidone, liquid temperature 40 to 70 ° C., processing time 2-1
About 0 minutes is good. A method of sequentially treating with several kinds of these treatment liquids is also possible.

It is effective to remove the residue by using an ultrasonic cleaning tank for these treatments and for washing with water after these treatments. Especially, it is very effective when removing a residue such as inside of a hole having a fine aspect ratio and a large aspect ratio. It is also effective to spray these chemicals and washing water with a spray or the like. Further, it is also a method that the processing residue can be efficiently and surely removed by sequentially performing the chemical solution treatment a plurality of times. The method of the present invention is particularly effective when the heat resistant resin contains at least polyimide.

[0009]

【Example】

Example 1 A 75 micrometer thick polyimide film (Ube Industries, trade name; Upilex S) was irradiated with KrF excimer laser light (oscillation wavelength 254 nm), and a part of the film was perforated. The energy density of the irradiated excimer laser light is 1.0 mJ / cm ² on the processed surface, and the frequency is 5
0 Hz, the number of pulses irradiated is 30 pulses. Also,
The processing method of this processing is the so-called mask imaging method, and a square shape (opening size 1 mm × 1
mm) mask was placed, and reduction projection was performed on the polyimide processed surface at a reduction ratio of 3.0. After the processing, when the surface was observed with a metallographic microscope and a scanning electron microscope, soot-like processing residues were observed on the polyimide surface near the processed portion. Next, an alkaline potassium permanganate aqueous solution immersion treatment (“permanganate treatment”) and a neutralization treatment were sequentially performed. First condition
Shown in the table. In this example, this treatment was performed twice. After the treatment, it was observed with a metallurgical microscope and a scanning electron microscope. As a result, the processing residue observed around the polyimide processed portion was removed. In this example, in order to effectively perform each treatment, the treatment was performed using an ultrasonic cleaning tank.However, even if the treatment is not used, the treatment time is lengthened, and the same treatment result is obtained by changing the conditions. Is obtained. In addition, a method of spraying a chemical solution or cleaning water onto the treated substrate by spraying or the like can effectively carry out the treatment similarly to the method using the ultrasonic cleaning tank. Further, as shown in this Example, repeating the "permanganate treatment → neutralization treatment" several times was more effective than increasing the permanganate treatment time.

Example 2 First, a two-layer MCF film (manufactured by Hitachi Chemical Co., Ltd.,
Product name: MCF-5510I (double-sided copper layer thickness: 18 μm each, central polyimide layer thickness: 75 μm)) copper wiring patterns and holes are formed by a normal photolithography process, and an evaluation wiring board (number of holes: 512, holes) The diameter was 120 μm). Excimer laser light (KrF laser, oscillation wavelength: 254 nm) was irradiated from one side of this evaluation wiring board. The energy density of the irradiated excimer laser light is 1.0 J / on the machined surface.
cm ² and frequency were 200 Hz. Further, the processing method was a scanning processing in which a copper hole pattern was used as a conformal mask and reciprocal scanning with laser light was performed. The processing conditions were a scan speed of 200 mm / cm ² and an irradiation frequency of 20 times.
When the wiring board for evaluation after laser processing was observed with a metallographic microscope and a scanning electron microscope, processing residues scattered and adhered by excimer laser processing were observed on the copper surface, the copper hole side wall and the polyimide hole side. Further, a measurement lead wire was electrically connected to each of the measurement terminals on both sides by soldering, and the insulation resistance was measured by a tester. As a result, it was 4.0 ohms. Next, a permanganate treatment and a neutralization treatment were sequentially performed. The conditions are shown in Table 1. In this example, this treatment was performed twice. The resistance value after the treatment was measured by an ordinary tester and confirmed to be 10 megohm or more. Further, when the insulation resistance was calculated from the current value when a voltage of 250 V was applied for 2 minutes between the measurement terminals with an insulation resistance meter,
It was 1.2 × 10 ¹² ohms. From this result, it was found that the conductive processing residue scattered and adhered by the laser processing adhered inside the hole was removed. Further, when the wiring board for evaluation after the treatment was observed with a metallographic microscope and a scanning electron microscope, the processing residues observed before the processing were removed on the copper surface, the copper hole side wall portion and the polyimide hole side portion.

Example 3 A wiring board (number of via holes: 32, via hole diameter: 80 micrometers) connected by blind via holes was produced. The manufacturing process is as follows. A single-sided copper-clad laminate was prepared as a base material. Next, the copper of this laminated plate was etched by a normal photolithography process to form a first wiring. On top of this, a polyimide adhesive film having a thickness of 25 micrometers (trade name AS-2, manufactured by Hitachi Chemical Co., Ltd.)
200) A copper foil (manufactured by Nippon Denshoku Co., Ltd., trade name SLP-12) was laminated and pressed by a vacuum press through two sheets. A portion of the copper foil, which is to be a blind via hole connection portion, was removed by etching using a normal photolithography process. In addition, excimer laser light (oscillation wavelength:
254 nm, energy density), and a portion to be a blind via was removed by a method of scanning laser light. The size of the irradiation area of the laser beam used for processing was 15 mm × 8 mm, and scanning was performed in the short direction of the irradiation area.
The energy density of the laser light was 1.0 J / cm ² , the frequency of the laser light was 200 Hz, the scanning speed was 300 mm / min, and the number of scans was 10 times. It was confirmed that the blind through hole to the lower wiring pad was formed. Confirmed with an electron microscope. Further, soot-like processing residues were observed on the copper foil around the processed via hole and on the polyimide resin in the blind via hole. For this wiring board, A: the treatment shown in Table 1 is continuously repeated twice, B: treatment condition total pressure 0.8 Torr (oxygen partial pressure / Freon partial pressure = 50/20), 150 W Plasma treatment was performed for 2 minutes, and C: no treatment was performed. In the cases of A and B, when observed with a microscope and a scanning electron microscope, the above-mentioned processing residue was removed. Next, electroless plating was applied to panel plating having a thickness of 2 micrometers and copper sulfate electroplating having a thickness of 15 micrometers, and the second wiring was formed by a normal photolithography method. When the cross section was observed with a metallographic microscope, B
In the case of, the polyimide immediately below the copper hole was etched back, and the copper plating thickness of the entire hole was thin, and especially the thickness of the copper plating immediately below the copper hole was considerably thin, whereas in case of A, the polyimide layer was etched back. also not observed, the copper plating layer was found not to be much thinner than the other portions. In the case of C, defective plating deposition was observed in a part of the inside of the hole. In case of A, B and C, 20 samples each (20
(0 measurement number) was produced and the connection reliability was evaluated by a thermal shock test. The test conditions are -65 ° C (30 minutes) → room temperature (2 minutes).
→ 150 ° C. (30 minutes) → room temperature (2 minutes) → −65 ° C. Repeat cycle. ± 1 based on the initial conduction resistance
When the resistance change of 0% or more occurred, the wire was broken and the conductivity after 1000 cycles = the number of conduction / the number of tests was determined. As a result, in case of A, B and C, 98%, 17% and 15% respectively
Met. Thus, by performing the permanganate treatment shown in the present invention as the post-treatment after laser processing, the connection reliability was significantly improved.

[0012]

[Table 1] ───────────────────────────────────   Processing order Processing name Processing liquid component Liquid temperature (℃) Time (min) ───────────────────────────────────     1 Water washing Pure water 25 ───────────────────────────────────     2 Permancanic acid treatment Potassium permancanate 60g / l 60 15                           Sodium hydroxide 38g / l                           Pure water remaining ───────────────────────────────────     3 Washing with pure water 25 ───────────────────────────────────     4 Washing with pure water 25 ───────────────────────────────────     5 Neutralization treatment Humanxylamine sulfate 5wt% 25 4                           Sulfuric acid 3vol%                           Pure water remaining ───────────────────────────────────     6 Washing with pure water 25 ───────────────────────────────────     7 Washing with pure water 25 ───────────────────────────────────

[0013]

According to the present invention, the precision of laser processing of heat-resistant resin and the reliability of processed products such as drilling small diameter holes in the wiring board manufacturing process can be dramatically improved.

─────────────────────────────────────────────────── ─── Continuation of the front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) B23K 26/00-26/42

Claims (2)

(57) [Claims] 1. A step of: (a) irradiating a heat-resistant resin with an excimer laser beam; (b) a step of treating with a permanganate alkaline solution; ( c ) a precipitated manganese compound in a solution containing a reducing agent.
(B), (c) including a step of removing by neutralization treatment
A method of laser-processing a heat-resistant resin, characterized in that the step is performed at least twice . 2. The laser processing method for heat-resistant resin according to claim 1, wherein the heat-resistant resin contains at least polyimide.