Summary of the invention
One of object of the present invention is just to provide the printed board of a kind of chromatic metallic base, the poor problem of temperature-sensitive, light sensitive effect existing to solve existing metal base circuit board.
Two of object of the present invention is just to provide the manufacture method of a kind of chromatic metallic base printed board, to meet device in the requirement aspect temperature-sensitive, light sensitive effect.
One of object of the present invention is achieved in that the printed board of a kind of chromatic metallic base, the chemical composition coating of having insulation on the surface of the metal substrate after anodic oxidation and surface colour processing, is hot bonding insulating medium layer and copper foil layer formation metal-based copper-clad plate successively by the surface at described metal substrate; On the surface of the described copper foil layer of described metal-based copper-clad plate through pad pasting, transfer printing line pattern and etching, take off after film, form the printed board of chromatic metallic base.
It is to adopt CuSO that the surface colour of described metal substrate is processed
4as electrolytic solution, carry out electrolytic coloring, or adopt electrostatic spraying mode to carry out spray colouration, or adopt organic dyestuff to carry out adsorption coloring.
Chromatic metallic base of the present invention printed board, except having retained all functions of common metal base printed board, has increased the different color of plate face compared with common metal substrate.Because color has difference, they are different to the energy-sensitive of heat, light, and the instructions for use meeting the special printing plate fields such as aviation, military affairs, meanwhile, for the equipment appearance of complete machine, has increased visual effect, elegant in appearance.
Two of object of the present invention is achieved in that the manufacture method of a kind of chromatic metallic base printed board, comprises the following steps:
A, the metal substrate that is 0.3~5mm to thickness carry out anodic oxidation and surface colour is processed, then by the concentrated sulfuric acid solution that is 22g/l in concentration, at 1~1.5A/dm
2the intensity of direct current under, flood described metal substrate 10~15min, after taking-up again in saturated potassium bichromate solution, flood 5~20min at the temperature of 95~100 ℃, at the chemical composition coating of the Surface Creation insulation of described metal substrate;
B, on the surface of described metal substrate, smear bonding glue-line, bonding insulating medium layer and copper foil layer successively, then under the condition of 180~190 ℃ of temperature, 280~300PSI pressure, compound 150~160 minutes of hot pressing, becomes metal-based copper-clad plate;
C, by plate shearing machine, the aniseed of described metal-based copper-clad plate is cut into and produces required PNL size according to the jigsaw size of design;
D, the surface label last layer dry film with manual/auto laminator at the copper foil layer of metal-based copper-clad plate, form photopolymer layer, and the pressure reel temperature in pad pasting process is 110~120 ℃, and pad pasting pressure is 3.5~5.0kg/cm
2; After pad pasting standing at least 15 minutes; Then surperficial contraposition, the exposure at described photopolymer layer with the yellow film of the production of making, vacuumizes 650~750mmHg, 7~9 grades of exposure progression; After standing at least 15 minutes, with developer solution, carry out development treatment again;
E, again through etching with after taking off film and processing, the line transitions will design needing is to the surface of the copper foil layer of described metal-based copper-clad plate;
F, the described metal-based copper-clad plate to etching and after taking off film and completing carry out the operation of silk-screen welding resistance ink in the usual way;
G, by designing requirement at the plate face silk-screen character of described metal-based copper-clad plate, after silk-screen, toast afterwards the printed board of chromatic metallic base; Baking condition is: 140~150 ℃, and 60~70 minutes.
Anodized process to described metal substrate in step a is:
1. the ungrease treatment of deoiling: with absorbent cotton adhesional wetting solvent, carry out wiping, except after degreasing, then the cotton wiping several times to clean; Described solvent can be selected trichloroethylene, ethyl acetate, acetone or butanone;
2. alkali cleaning is processed: with the sodium hydroxide solution of 3mol/L, clean 15~25s, then wash twice;
3. pickling processes: clean 1 minute with the salpeter solution of 2mol/L, then wash twice;
4. oxidation processes: with the concentrated sulfuric acid of 22g/L, at 1~1.5A/dm
2direct current intensity under flood 10~15min, then in saturated potassium bichromate solution, flood 5~20min at 95~100 ℃, then wash twice;
5. can be at the diaphragm of Surface Creation layer of transparent, uniformity and the porous of described metal substrate after drying, so that follow-up painted to described metal substrate.
The surface colour of metal substrate of the present invention is processed can various ways.
Mode one: the surface colour processing procedure to described metal substrate in step a can adopt CuSO
4as electrolytic solution, carry out electrolytic coloring, be about to described metal substrate that anodic oxidation is good as negative electrode, at CuSO
4under the effect of electrolytic solution, the fine and close aubergine copper film uniformly of surperficial electrolysis generation at described metal substrate shows as coppery under light irradiates.
Mode two: can adopt electrostatic spraying mode to carry out spray colouration to the surface colour processing procedure of described metal substrate in step a, detailed process is:
1. degreasing: the H that is 100~150g/L in mass concentration by described metal substrate
2sO
2 middle immersion 3~5 minutes, carries out ungrease treatment;
2. alkali cleaning: soak 5~15 minutes in the sodium hydroxide solution that is 45~85g/L in mass concentration by the described metal substrate after degreasing, carry out alkali cleaning processing;
3. bright dipping: the described metal substrate after alkali cleaning is immersed in to the H that concentration is 200~250g/L
2sO
2with concentration be the H of 3~5 g/L
2nO
3mixed solution in 3~5min, with in and the surface of the alkalinous metal salt of metallic substrate surfaces clean described metal substrate;
4. anodic oxidation: in the concentrated sulfuric acid that is 22g/L in concentration by the described metal substrate after surface treatment, at 1~1.5A/dm
2direct current intensity under flood 10~15min, then in saturated potassium bichromate solution, flood 5~20min at 95~100 ℃, then wash twice, thereby form the porous anodized film of one deck on the surface of described metal substrate;
5. half sealing of hole: the described metal substrate after anodized is immersed in hole sealing solution, and described hole sealing solution is NiF
24H
2o solution, nickel ion content 0.8~1.5g/L wherein, content of fluoride ion 0.4~0.6g/L, pH value: 6 ± 0.5, sealing of hole speed 1um/min, 1~3 minute sealing of hole time;
6. electrostatic spraying: electrostatic spraying is carried out on the surface at the described metal substrate after sealing of hole is processed, and forms and films uniformly on described metal substrate, and the film thickness of spraying is 15~30 μ m;
7. drying and packaging: in drying room, the described metal substrate after electrostatic spraying is dried 2 minutes at 180 ℃ of constant temperature, be cooled to 40~50 ℃ after taking-up, then detect, pack.
Mode three: can adopt organic dyestuff to carry out adsorption coloring to the surface colour processing procedure of described metal substrate in step a, detailed process is:
1. the ungrease treatment of deoiling: with absorbent cotton adhesional wetting solvent, carry out wiping, except after degreasing, then the cotton wiping several times to clean; Described solvent can be selected trichloroethylene, ethyl acetate, acetone or butanone;
2. alkali cleaning is processed: with the sodium hydroxide solution of 3mol/L, clean 15~25s, then wash twice;
3. pickling processes: clean 1 minute with the salpeter solution of 2mol/L, then wash twice;
4. oxidation processes: with the concentrated sulfuric acid of 200 ± 30g/L, 20 ± 2 ℃ of temperature, at 1.4 ± 0.3A/dm
2direct current intensity under flood 10~20min, then in saturated potassium bichromate solution, flood 5~20min at 95~100 ℃, then wash twice;
5. can be at the diaphragm of Surface Creation layer of transparent, uniformity and the porous of described metal substrate after drying, so that follow-up painted to described metal substrate;
6. the mechanism of the adsorption coloring of organic dyestuff: the normal pH value of versicolor organic dyestuff: 4~5.5, temperature 60 C, immersion time 5~15min, the anion of dyestuff enters into the oxidation fenestra of described metal substrate, and (aperture is generally 120 * 10
-16m), in, by suction-operated, be adsorbed on aluminium cations;
7. painted rear sealing of hole: adopt deionized water or distilled water, by boiling water, painted aluminium base is carried out to sealing of hole, at least 20 minutes.
In the hot pressing of step b, for the thick described copper foil layer of 35 μ m, the THICKNESS CONTROL of bonding glue-line is at 120 ± 10 μ m.
Development conditions in steps d is: the concentration of sodium carbonate is 1.0%, and temperature is 30 ± 2 ℃, the pressure 1.0~1.5kg/cm of development
2.
In step e, the specific gravity control of etching solution is 1.26~1.32, content of copper ion 110~170g/L, and acid equivalent 1.0~2.0 (N), 50 ℃ of etch temperature, speed is controlled 1.5m/min; In taking off film section, NaOH concentration 2~3%, 50~60 ℃ of temperature, developing powder 1.8~2.2m/min.
Chromatic metallic base printed board manufacture method of the present invention has solved the technique difficult problem of metal substrate in anodic oxidation and electrolytic coloring processing procedure; By the control of the concentration control to electrolytic solution and current density, electrolysis time, solved well that rete is not painted, do not paint in part, of light color and easily take off, have after painted white point, painted growing dim or the problem such as dim.Because the object of different colours is different to the absorbability of light, such as red object reflect red, the light of other wave band all can be absorbed, and white object reflects whole light, and black object absorbs whole light.So, when Metal Substrate face is caught after different colours, just can reach different reflections and the effect that absorbs light energy.Facts have proved, black heat absorption capacity is the strongest, and redness is taken second place, and white is the most weak.By light, be radiated at the metallic substrate surface of different colours, produce types such as absorbing light, reverberation, and along with Metal Substrate Surface absorption light energy number and the variations in temperature of generation is different, recycling photoelectric sensor principle after light energy conversion becomes a kind of signal of telecommunication as a kind of bang-bang control assembly.
Embodiment
Embodiment 1
As shown in Figure 1, the thickness of metal substrate 1 is 0.3~5mm, first metal substrate 1 is carried out to anodized and surface colour processing, chemical composition coating 2 in the Surface Creation insulation of metal substrate 1, on the surface of metal substrate 1, be hot bonding successively after insulating medium layer 3 and copper foil layer 4, form metal-based copper-clad plate.On the surface of the copper foil layer 4 of metal-based copper-clad plate through pad pasting, transfer printing line pattern and etching, take off after the operations such as film, form chromatic metallic base of the present invention printed board.
The surface colour of metal substrate 1 is processed can adopt CuSO
4as electrolytic solution, carry out electrolytic coloring, or adopt electrostatic spraying mode to carry out spray colouration, or adopt organic dyestuff to carry out adsorption coloring.
Embodiment 2
The manufacture method of chromatic metallic base of the present invention printed board comprises the following steps:
1, the metal substrate that is 0.3~5mm to thickness carries out anodic oxidation and surface colour is processed, then by the concentrated sulfuric acid solution that is 22g/l in concentration, at 1~1.5A/dm
2the intensity of direct current under, flood described metal substrate 10~15min, after taking-up again in saturated potassium bichromate solution, flood 5~20min at the temperature of 95~100 ℃, at the chemical composition coating of the Surface Creation insulation of described metal substrate.The anodic oxidation of metal substrate and surface colour are processed, mainly by chemistry and electrochemical treatments are carried out in the surface of metal substrate, make it to there is certain roughness, and on its surface without the chemical composition coating that becomes certain thickness high-insulativity, make this resin film layer there is high resistance, the performance such as breakdown voltage resistant.
First, to the anodized process of metal substrate, be:
1. the ungrease treatment of deoiling: with absorbent cotton adhesional wetting solvent, carry out wiping, except after degreasing, then the cotton wiping several times to clean; Described solvent can be selected trichloroethylene, ethyl acetate, acetone or butanone;
2. alkali cleaning is processed: with the sodium hydroxide solution of 3mol/L, clean 15~25s, then wash twice;
3. pickling processes: clean 1 minute with the salpeter solution of 2mol/L, then wash twice;
4. oxidation processes: with the concentrated sulfuric acid of 22g/L, at 1~1.5A/dm
2direct current intensity under flood 10~15min, then in saturated potassium bichromate solution, flood 5~20min at 95~100 ℃, then wash twice;
5. can be at the diaphragm of Surface Creation layer of transparent, uniformity and the porous of described metal substrate after drying, so that follow-up painted to described metal substrate.
Secondly, to the surface colour processing procedure of described metal substrate, be: adopt CuSO
4as electrolytic solution, carry out electrolytic coloring, be about to metal substrate that anodic oxidation is good as negative electrode, at CuSO
4under the effect of electrolytic solution, the fine and close aubergine copper film uniformly of surperficial electrolysis generation at metal substrate shows as coppery under light irradiates.
Principle to the electrolytic coloring of metal substrate is, first form sulphuric acid oxidation coating, then in coloring solution, carry out electrolytic coloring (metallic in inorganic salts is deposited on the result of oxidation fenestra bottom), the tone of electrolytic coloring depends on the distinctive color of slaine itself.
Take aluminium base as example, after aluminium carries out anodized in sulfuric acid solution, generate one deck artificial oxidation film on product surface, the surface of this layer of oxide-film is porous, claims porous layer.And the bottom of oxide-film contacts with aluminum substrate, be fine and close oxide-film thin layer, also referred to as active layer or barrier layer.This aluminium with anode oxide film is soaked in the electrolysis of certain slaine of people, and as an electrode (negative electrode), and another extremely can be with simple metal plate or corrosion resistant plate etc. as sun level.When the two poles of the earth pass to alternating current simultaneously (general under the condition of low-voltage and low current density), aluminum products just automatically become negative electrode, and face discharges hydrogen from it, it is poor that metal ion in while metallic solution forms strong ion concentration near aluminum products, and be deep on active layer by porous layer, alternately bear violent reduction and oxidation slowly.Also be that active layer attracts metal ion consumingly, and with the negative electrostatic charge producing there, electric discharge and precipitating metal or metal oxide occur repeatedly, and be deposited on 3~6um place, bottom of oxide-film minute aperture, the metal particle amount of separating out is about 0.01g/dm
2.It is hair-like, spherical or granular that these particulates are conventionally, and its diameter is 10~15nm, and length is several microns.Under effect of light, these metal particle generation diffraction, just make oxide-film present shades of colour.
The good aluminium flake of the anodic oxidation of usining is as negative electrode, and plumbous net is anode, CuSO
4as electrolytic solution, carry out electrolysis.
Major parameter is: CuSO
4the concentration of electrolytic solution is: 20~25%; Current density: 10~20mA/cm
2, electrolysis time: 5~10min.
Anode: H
2o-2e
-→ 1/2 O
2+ 2H
+
Negative electrode: Cu
2++ 2e
-→ Cu
The good aluminium flake of anodic oxidation, as negative electrode, generates fine and close Cu uniformly and is attached to its surface during electrolysis, form mauve copper film, thereby show as coppery under the irradiation of light.
The surface of electrolytic coloring has the hardness identical with sulphuric acid oxidation coating and anti-wear performance, and rete has particularly preferred UV resistant irradiation performance, and heat resistance is good, and has good corrosion resistance etc.
Electrolytic coloring principle: first form sulphuric acid oxidation coating, then in coloring solution, carry out electrolytic coloring (metallic in inorganic salts is deposited on the result of oxidation fenestra bottom), the tone of electrolytic coloring depends on the distinctive color of slaine itself, referring to table 1.
table 1: the different tones that aluminium extremely produces after electrolytic coloring after sunization at oxygen in different metal electrolytic solution.
2, hot-forming: on the surface of metal substrate, smear bonding glue-line, bonding insulating medium layer and copper foil layer successively, then under the condition of 180~190 ℃ of temperature, 280~300PSI pressure, compound 150~160 minutes of hot pressing, becomes metal-based copper-clad plate; In hot pressing, for the thick described copper foil layer of 35 μ m, the THICKNESS CONTROL of bonding glue-line is better at 120 ± 10 μ m.When glue-line is too thin, the infiltration aluminium sheet that adhesive can not be good and roughening of copper foil face, can cause puncture voltage to decline.And glue-line is blocked up, because mobility is excessive, cause Copper Foil to be seen rough and uneven in surface.In addition, for Copper Foil and aluminium sheet, its roughness is larger, is easily infiltrated, so glue-line needn't be too thick.For guaranteeing the operability of product quality and experiment, bondline thickness is controlled at 120 ± 10 μ m and is advisable, and metal-based copper-clad plate is normally composited through HTHP with metal substrate, insulating medium layer, the Copper Foil of 0.3~5 mm.
In hot-forming process, to control following technological parameter well:
1. according to the suitable contact of the different choice of resin system and dielectric and first pressing; 2. forming temperature is 180 ℃; 3. briquetting pressure 300PSI: 4. molding time is 150 minutes.
3, by plate shearing machine, the aniseed of metal-based copper-clad plate is cut into and produces required PNL size according to the jigsaw size of design.
4, the surface label last layer dry film at the copper foil layer of metal-based copper-clad plate with manual/auto laminator, forms photopolymer layer, and the pressure reel temperature in pad pasting process is 110~120 ℃, and pad pasting pressure is 3.5~5.0kg/cm
2.After pad pasting standing at least 15 minutes, then surperficial contraposition, the exposure at described photopolymer layer with the yellow film of the production of making, vacuumized 650~750mmHg, 7~9 grades of exposure progression; After standing at least 15 minutes, with developer solution, carry out development treatment again.Development conditions is: the concentration of sodium carbonate is 1.0%, and temperature is 30 ± 2 ℃, the pressure 1.0~1.5kg/cm of development
2.
5,, again through etching with after taking off film and processing, the line transitions will design needing is to the surface of the copper foil layer of described metal-based copper-clad plate.By the acid CuCl in copper face region exposing after photographic fixing
2solution dissolves, and this process is etching.The specific gravity control of etching solution is 1.26~1.32, content of copper ion 110~170g/L, and acid equivalent 1.0~2.0 (N), 50 ℃ of etch temperature, speed is controlled 1.5m/min.Wet film, dry film effect by highly basic (being generally NaOH) solution with the light that exposed to the sun, take off the film on figure, remaining circuit and the copper face that has figure, and this process is taking off film.In taking off film section, the concentration of NaOH is 2~3%, and temperature is 50~60 ℃, and developing powder is 1.8~2.2m/min.
6, the described metal-based copper-clad plate to etching and after taking off film and completing carries out the operation of silk-screen welding resistance ink in the usual way.Silk-screen welding resistance ink is generally white or black.First by the whole plate printing of automatic screen printer last layer welding resistance ink; Standing more than 15 minutes; Prebake conditions is 72~75 ℃ again, 40~45 minutes, allows ink solidification; Then with the yellow film aligning of the production of making, exposure, vacuumize 650~750mmHg, 11~13 grades of exposure progression; And then be statically placed in more than 15 minutes; Contraposition, exposure OK plate are developed, and the concentration of developer solution sodium carbonate is 1.0%, and temperature is 30 ± 2 ℃, the pressure 1.0~2.5kg/cm of development
2, the speed 2.5~3.5m/min of development.
7, by designing requirement at the plate face silk-screen character of described metal-based copper-clad plate, after silk-screen, toast afterwards the printed board of chromatic metallic base.Baking condition is: 140~150 ℃, and 60~70 minutes.
8, external form processing, first needs hole, drilling pipe position, then computer boring, gong profile, V-CUT.Common metal base circuit board need adopt special-purpose bit, gong cutter and V-CUT cutter, is convenient to reduce burr and the burr in boring and sharp processing process.During operation, fold for general one one, and parameter setting wants slow a lot of with respect to common FR-4 plate.
9, circuit, anti-welding, word, surface treatment etc. are with reference to requiring normal inspection; Pay special attention to overall dimension and Pore Diameter Detection; Aperture and profile are not according to being subject to burr, burr; Between circuit, not according to being subject to any foreign impurity at plate face, during anti-Hi-pot test, puncture.
Embodiment 3
The manufacture method of the chromatic metallic base printed board of the present embodiment, substantially with embodiment 2, is just to adopt electrostatic spraying mode to carry out spray colouration to the surface colour processing procedure of metal substrate, and detailed process is:
1. degreasing: the H that is 100~150g/L in mass concentration by described metal substrate
2sO
2 middle immersion 3~5 minutes, carries out ungrease treatment.
2. alkali cleaning: soak 5~15 minutes in the sodium hydroxide solution that is 45~85g/L in mass concentration by the described metal substrate after degreasing, carry out alkali cleaning processing.
3. bright dipping: the described metal substrate after alkali cleaning is immersed in to the H that concentration is 200~250g/L
2sO
2with concentration be the H of 3~5 g/L
2nO
3mixed solution in 3~5min, with in and the surface of the alkalinous metal salt of metallic substrate surfaces clean described metal substrate.
4. anodic oxidation: in the concentrated sulfuric acid that is 22g/L in concentration by the described metal substrate after surface treatment, at 1~1.5A/dm
2direct current intensity under flood 10~15min, then in saturated potassium bichromate solution, flood 5~20min at 95~100 ℃, then wash twice, thereby form the porous anodized film of one deck on the surface of described metal substrate; Anodised object is exactly mainly on aluminium base surface, to form the porous anodized film of one deck, for sealing of hole and the electrostatic spraying paint vehicle of rear operation lays the first stone.
5. half sealing of hole: technological requirement is normal-temperature hole sealing (being called again cold seal hole), the metal substrate being about to after anodized immerses in hole sealing solution, and described hole sealing solution is NiF
24H
2o solution, nickel ion content 0.8~1.5g/L wherein, content of fluoride ion 0.4~0.6g/L, pH value: 6 ± 0.5, sealing of hole speed 1um/min, 1~3 minute sealing of hole time.
Sealing of hole principle is: nickel ion is deposited in the micropore of anode oxide film of metal substrate at normal temperatures.But antianode oxide-film can not all seal, must remain only about half of fenestra, so that the paint vehicle of adsorption electrostatic spraying.The control of half sealing of hole, is under the concentration and the metastable situation of deposition velocity of hole sealing solution, mainly by the time of deposition, controls, and general sealing of hole sedimentation time is no more than the degree that can guarantee half sealing of hole for 3 minutes.
6. electrostatic spraying: electrostatic spraying is carried out on the surface at the metal substrate after sealing of hole is processed, and forms and films uniformly on metal substrate, and the film thickness of spraying is 15~30um.Specifically metal substrate is put into the spray room that carries out automatic coating, the electrostatic generator in spraying equipment produces the adjustable DC high pressure of 20~90KV, output current 10~20uA; The defeated paint amount of spraying equipment is controlled at 200ml/min, and the resistivity of paint amount is generally at 45M Ω CM.During work, spray gun (being atomizer) connects negative pole, metal substrate connects anodal and ground connection, under the action of high voltage of high voltage source, between the end of spray gun and metal substrate, just form an electrostatic field, coating sprays after nozzle atomization, and the paint particles being atomized is charged because contacting when the edge of the spray dish by spray gun muzzle and spray cup, when produce through corona discharge gas ionization zone time, will increase again its surface charge density.These electronegative paint particles are under electrostatic field, and the apparent motion of the metal substrate of guide polarity, and being deposited on the surface of metal substrate, forms and film uniformly.
7. drying and packaging: in drying room, the described metal substrate after electrostatic spraying is dried 2 minutes at 180 ℃ of constant temperature, after taking-up, with cold wind, be cooled to 40~50 ℃, the quality of artificial visually examine's testing product, packs qualified product, during blanking packing, must handle with care, be strictly on guard against and damage.
Embodiment 4
The manufacture method of the chromatic metallic base printed board of the present embodiment, substantially with embodiment 2, is just to adopt organic dyestuff to carry out adsorption coloring to the surface colour processing procedure of metal substrate, and detailed process is:
1. the ungrease treatment of deoiling: with absorbent cotton adhesional wetting solvent, carry out wiping, except after degreasing, then the cotton wiping several times to clean.Described solvent can be selected trichloroethylene, ethyl acetate, acetone or butanone.
2. alkali cleaning is processed: with the sodium hydroxide solution of 3mol/L, clean 15~25s, then wash twice.
3. pickling processes: clean 1 minute with the salpeter solution of 2mol/L, then wash twice.
4. oxidation processes: with the concentrated sulfuric acid of 200 ± 30g/L, 20 ± 2 ℃ of temperature, at 1.4 ± 0.3A/dm
2direct current intensity under flood 10~20min, then in saturated potassium bichromate solution, flood 5~20min at 95~100 ℃, then wash twice.
8. can be at the diaphragm of Surface Creation layer of transparent, uniformity and the porous of metal substrate after drying, so that follow-up painted to metal substrate.
9. the mechanism of the adsorption coloring of organic dyestuff: the normal pH value of versicolor organic dyestuff is 4~5.5, temperature 60 C, immersion time 5~15min, the anion of dyestuff enters into the oxidation fenestra of metal substrate, and (aperture is generally 120 * 10
-16m), in, by suction-operated, be adsorbed on metal cation.
Painted rear sealing of hole: adopt deionized water or distilled water, by boiling water, painted metal substrate is carried out to sealing of hole, at least 20 minutes.