628results about "Circuit precursor manufacture" patented technology

The invention discloses a curved circuit three-dimensional printing-oriented base material surface modification and adhesive force enhancement method, which comprises the following steps of: performing surface modification on the surface of an insulating curved surface base material, and integrally plating copper after modification, so that a layer of uniform conductive copper film is formed on the surface of the base material; anti-etching mask ink is selectively jet-printed on the base material, curing is carried out after jet printing is completed until the anti-etching mask ink is completely dried, and an anti-etching film with a conductive pattern is formed on the surface of the insulation curved surface base material; then, the conductive copper film is soaked in etching liquid for selective etching, and the conductive copper film which is not covered with the anti-etching film is gradually dissolved until the original insulating curved surface base material is exposed; and then soaking in an alkaline solution until the anti-etching film with the conductive pattern is completely dissolved and falls off to obtain the insulating curved-surface base material with a clean surface and a complete conductive pattern. According to the method disclosed by the invention, the adhesive force between the conductive material and the insulating curved surface base material is greatly enhanced, and high-precision and high-reliability preparation of the curved surface circuit is realized.

The invention discloses a high-precision etching device for manufacturing a copper-clad plate and an etching method, and relates to the technical field of copper-clad plate etching, the high-precision etching device comprises a box body, the outer wall of the top of the box body is fixedly connected with a liquid inlet pipe used for conveying etching liquid, and a spraying assembly used for etching a copper-clad plate body is arranged in the box body; the spraying assembly comprises a corrugated pipe fixedly connected to the end, located in the box body, of the liquid inlet pipe, one end of the corrugated pipe is fixedly connected with a first liquid guide pipe, the two ends of the first liquid guide pipe are fixedly connected with second liquid guide pipes, and the two ends of each second liquid guide pipe are connected with spraying pipes in an inserted mode. In the etching process of the copper-clad plate, the copper-clad plate can be kept stable even if being impacted by etching liquid, the side clamp only acts on the side face of the copper-clad plate body, the front face and the back face of the copper-clad plate body cannot be shielded, etching dead angles are effectively avoided, the etching precision is further improved, and meanwhile the side face clamping can prevent the side etching phenomenon.

The invention discloses a copper-clad plate as well as a middle layer and a preparation method and application thereof, and belongs to the technical field of copper-clad plates. The preparation method of the intermediate layer for the copper-clad plate comprises the following steps: orthogonally weaving PBO fibers and glass fibers to obtain blend fibers; the mass ratio of the PBO fibers to the glass fibers is (10: 90)-(60: 40); carrying out modification treatment on the blend fibers to obtain modified blend fibers; dipping the modified blend fiber in a resin-containing dipping solution; and drying the impregnated modified blend fiber. The preparation method is simple and easy to operate, the PBO fibers and the glass fibers are orthogonally woven according to a specific ratio, so that on one hand, the blend fibers have the advantages of the PBO fibers and the glass fibers, on the other hand, the anisotropy of the blend fibers is effectively optimized, and the obtained copper-clad plate has relatively low dielectric loss and expansion coefficient; the peeling strength, the heat resistance and the flexibility are better.

The invention relates to the field of copper-clad plates, and discloses a low-dielectric-constant high-performance copper-clad plate and a preparation method thereof.The preparation method comprises the specific steps that epoxy resin, phenolic resin, polyphenyl ether modified resin, modified nano silicon dioxide and the like are taken and mixed to obtain a resin glue solution; impregnating glass fabric in the resin glue solution to obtain a prepreg; laminating prepregs, and covering copper foil for hot pressing; the polyphenyl ether modified resin comprises epoxy resin, diallyl cyanate and fluorine-containing polyphenyl ether resin prepared by reaction of polyphenyl ether, bisphenol AF and benzoyl peroxide; the modified nano silicon dioxide is prepared by reacting allyl glycidyl ether, vinyltriethoxysilane and phenyltris (dimethylsiloxane) silane, then grafting with a phosphorus-containing intermediate to prepare a modified additive, and grafting with nano silicon dioxide, and the phosphorus-containing intermediate is prepared by reacting phenylphosphoryl dichloride and eugenol. The copper-clad plate with high flame retardance, high peel strength, heat resistance and low dielectric constant is prepared.

An integrated machine for automatic cutting, polishing, stacking, and unloading of substrates, including a laser cutting machine, a mechanical laser arm, a polishing machine, a polishing device, a first finished product placement rack, a second finished product placement rack, and an automatic stacking device. The mechanical laser arm is fixed on the frame of the laser cutting machine, the polishing device is fixed on the polishing machine, and the first finished product placement rack and the second finished product placement rack are arranged on both sides of the automatic stacking device. The present disclosure can achieve cutting the substrates of any size, and can automatically polish the edges of the cut substrates. The present disclosure has the characteristics of automation, integration, and multi-functionality, effectively reducing the number of supporting equipment and occupying space.

The present invention relates to a process for preparing multi-material laminates for printed circuit boards that envisages the formation of a stack of plastic laminates, indicated below as "packages", separated by plates of electrically insulating material, and the heating of the stack in the presence of at least two temperature detectors that allow the uniformity of the temperature to be obtained along the whole stack, and a system for producing said laminates.

The invention discloses an automatic laminating device for a copper-clad plate. The automatic laminating device comprises a bottom frame, a conveying main body, a protective cover, a top cover, a glue spraying head, a connecting pipe, a rectangular groove, an assembling mechanism and a pressing mechanism, the assembling mechanism and the pressing mechanism are optimally arranged, four strip frames of the assembling mechanism are used for stacking the aluminum substrates, copper plates and the aluminum substrates are limited through a first positioning structure and a second positioning structure during laminating processing, and one aluminum substrate falls off at a time under the action of a first discharging structure and a second discharging structure, so that the production efficiency is improved, and the production efficiency is improved. The aluminum substrate is pressed on the copper plate through the pressing mechanism so that the aluminum substrate can fall on the copper plate, the attaching regularity of the copper plate and the aluminum substrate can be guaranteed, then the moving and pressing structure of the pressing mechanism rotates and moves downwards to make contact with the upper portion of the aluminum substrate, the aluminum substrate is pressed on the copper plate from right to left through the moving and pressing structure, air between the aluminum substrate and the copper plate is exhausted, and the attaching efficiency is improved.

The invention relates to the field of copper-clad plates, and discloses a high-performance flame-retardant low-dielectric-loss copper-clad plate and a preparation method thereof.The copper-clad plate comprises epoxy resin, benzoxazine resin, composite filler, carboxyl-terminated nitrile rubber, an active diluent, a curing agent and the like; the composite filler is prepared by compounding flame-retardant modifier grafted graphene oxide and epoxy silane modified silicon dioxide hollow spheres; according to the flame-retardant modifier, boric acid and pentaerythritol are used for preparing a double-terminal hydroxyl boron-containing intermediate, then dichlorodiphenyl silane and phenylphosphonic dichloride react with hydroxyl groups at the two ends of the intermediate to prepare a flame-retardant intermediate, and amino silane and vanillic aldehyde react with chlorine atoms at the two ends of the intermediate to prepare an aldehyde modified flame-retardant intermediate; the copper-clad plate prepared by the preparation method disclosed by the invention is low in dielectric constant and dielectric loss, high in heat conductivity coefficient and good in flexibility, and also has excellent heat resistance and flame retardance.

The present invention relates to a copper-clad plate with plated-through holes, a circuit board with plated-through holes, and manufacturing methods therefor. Specifically, a method for manufacturing a copper-clad plate with plated-through holes comprises the following steps: drilling an insulating substrate; performing a pre-treatment on the substrate with holes; simultaneously treating the surface and hole walls of the substrate by means of a combination of a plurality of physical vapor deposition methods, so as to form conductive seed layers on the surface and hole walls of the substrate, thereby obtaining a metallized substrate with plated-through holes; and performing electroplating thickening on the metallized substrate, so as to obtain a copper-clad plate with plated-through holes.

A ceramic circuit board includes a ceramic substrate and a metal plate bonded together via a bonding layer, wherein when the ceramic circuit board is observed through a cross-section defined by a thickness direction and lateral direction of the ceramic circuit board: a side surface of the metal plate has an inclined shape; and the bonding layer has a bonding-layer protruding portion which protrudes by 20 μm or more and 150 μm or less from an edge where the bonding layer is in contact with the side surface of the metal plate. The shape and Vickers hardness of the side surface of the metal plate are controlled. The ceramic substrate is preferably a silicon nitride substrate.

The invention relates to the technical field of electronic manufacturing, and discloses a circuit board printing manufacturing device which comprises a conveying belt, one end of the conveying belt is provided with a board placing device used for storing solder resist ink needing to be coated, one side of the board placing device is provided with two brushing devices, and the two brushing devices are arranged on the conveying belt. A fixing plate is arranged between the two brushing devices, the fixing plate is fixedly mounted on a fixing mounting plate of the conveying belt, a square rod is arranged between the fixing plate, one end of the square rod is rotationally connected with a gear, the other side of the gear is fixedly connected with a sliding square block, the other end of the sliding square block is slidably connected with a clamping block, and the clamping block is fixedly connected with the clamping block. One side of the clamping block communicates with an air pipe used for adsorbing a copper-clad plate, the square rod is sleeved with a torsional spring, and one end of the torsional spring is fixedly connected with the square rod. The circuit board printing and manufacturing device can fix the position of the copper-clad plate after the copper-clad plate is turned over.

The invention relates to the technical field of preparation of copper-clad plates, and discloses a preparation method of a phosphorus-containing flame-retardant halogen-free copper-clad plate, which comprises the following steps: uniformly stirring and mixing bisphenol A type epoxy resin, linear phenolic resin, phosphorus-containing tetraglycidyl ester and the like, smearing the mixture on E-glass fabric, baking to obtain prepregs, overlapping eight prepregs, coating copper foils on the two surfaces, and drying to obtain the phosphorus-containing flame-retardant halogen-free copper-clad plate. According to the preparation method, bisphenol A type epoxy resin is taken as matrix resin, linear phenolic resin is taken as a curing agent, phosphorus-containing tetraglycidyl ester is added, flame-retardant elements and a heat-resistant structure contained in the phosphorus-containing tetraglycidyl ester are utilized, the flame-retardant halogen-free copper-clad plate is obtained, and the flame-retardant halogen-free copper-clad plate is obtained. The flame retardant property, the heat resistance and the mechanical property of the copper-clad plate material are improved.

Disclosed is a copper foil to which a carrier foil is attached, which has favorable peel strength under high-temperature pressing conditions, the copper foil to which the carrier foil is attached comprising: a carrier foil; a release layer on the carrier foil; a heat-resistant layer on the release layer; and an ultra-thin copper foil on the heat-resistant layer, in which a buffer layer of a nickel alloy is interposed between the release layer and the heat-resistant layer.

The invention discloses a press-fit preparation method of a high-thermal-conductivity circuit board and the high-thermal-conductivity circuit board, and the preparation method comprises the steps: carrying out the dispersion and solidification of a liquid metal gallium-indium alloy and fiber mixture in an inert argon atmosphere, and fusing with a substrate, and obtaining a self-adaptive heat-conduction substrate; carrying out gradient deposition and etching treatment on the self-adaptive heat conduction base material to obtain a gradient spacing template; carrying out electrospinning infiltration and heat treatment on the gradient spacing template to obtain a base material containing a dynamic heat-conducting network; conducting layer pre-pressing treatment is conducted on the base material containing the dynamic heat conduction network, and a pre-assembled plate is obtained; performing staged dynamic pressing treatment on the pre-assembled board to obtain a molded circuit board; and performing surface spraying and deposition treatment on the molded circuit board to obtain the high-thermal-conductivity circuit board. The problems of poor heat flow path, poor interface bonding performance and the like in the prior art are solved, the heat management effect is remarkably improved, and the reliability and performance of an electronic product are remarkably improved.

The present application discloses a method for laminating and preparing a high thermal conductivity circuit board and a high thermal conductivity circuit board. The preparation method comprises: dispersing and curing a liquid metal gallium-indium alloy and a fiber mixture in an inert argon atmosphere, and fusing the mixture with a matrix to obtain an adaptive thermal conductive substrate; performing gradient deposition and etching on the adaptive thermal conductive substrate to obtain a gradient spacing template; performing electrospinning infiltration and heat treatment on the gradient spacing template to obtain a substrate containing a dynamic thermal conductive network; performing a conductive layer pre-pressing treatment on the substrate containing the dynamic thermal conductive network to obtain a pre-assembled plate; performing a staged dynamic lamination treatment on the pre-assembled plate to obtain a molded circuit board; and performing surface spraying and deposition treatment on the molded circuit board to obtain the high thermal conductivity circuit board. The present application solves the problems of poor heat flow path and poor interface bonding in the prior art, significantly improving the thermal management effect and significantly improving the reliability and performance of electronic products.

The invention relates to a copper substrate embedding method for separated special-shaped copper blocks and a circuit board, and the method comprises the following steps: processing a plurality of special-shaped copper blocks with preset shapes on a copper plate, and reserving a plurality of connecting ribs which are not completely cut off between the adjacent special-shaped copper blocks; a gap between every two adjacent special-shaped copper blocks is filled with resin; a heat-conducting insulating layer and a copper foil are sequentially overlaid on the two opposite faces of the copper plate to form a stacked structure, and a substrate is formed through high-temperature pressing; an isolation groove is formed in the position, corresponding to the connecting rib, of the substrate, and the isolation groove cuts off the connecting rib; the isolation groove is filled with resin, and the resin overflowing out of the plate surface is rubbed down; and conducting treatment: forming a continuous conductive copper layer on the surface of the resin filling area. According to the invention, no copper groove needs to be buried, the copper block can be processed into a specific shape, and the distance between two adjacent special-shaped copper blocks is controlled to be 1.0 mm, so that the number and the area of the copper blocks buried in the substrate are greatly increased, and the heat dissipation performance and the electrical performance of the circuit board are improved.

The present invention relates to the field of copper clad laminates, and discloses a copper clad laminate with low dielectric constant and high performance and a preparation method thereof. The specific steps are as follows: taking epoxy resin, phenolic resin, polyphenylene ether modified resin, modified nano-silica, etc. and mixing them to obtain a resin glue solution; impregnating glass fiber cloth in the resin glue solution to obtain a prepreg; taking the prepregs and laminating them and hot pressing them with copper foil; the polyphenylene ether modified resin includes epoxy resin, diallyl cyanate, and a fluorinated polyphenylene ether resin prepared by reacting polyphenylene ether, bisphenol AF, and benzoyl peroxide; the modified nano-silica is prepared by reacting allyl glycidyl ether and vinyltriethoxysilane with phenyltris(dimethylsilyl)silane, and then grafting it with a phosphorus-containing intermediate to form a modified additive, and grafting the modified additive with nano-silica. The phosphorus-containing intermediate is prepared by reacting phenylphosphoryl dichloride and eugenol. A copper clad laminate with high flame retardancy, high peel strength, and heat-resistant low dielectric constant is prepared.

Provided are: a fluororesin sheet having both a low linear expansion coefficient (CTE) and improved adhesion to a copper foil having a smooth surface; and a copper-clad laminate using the fluororesin sheet. A fluororesin sheet containing a fluororesin and silica particles, the fluororesin sheet having an oxygen element ratio of 3.0 at% or more and a linear expansion coefficient (CTE) of 100 ppm / DEG C or less when measured by X-ray photoelectron spectroscopy (XPS) on one or both surfaces thereof.

The invention relates to the technical field of copper foil surface treatment, in particular to a copper foil and a preparation method and application thereof. The copper foil comprises an electrolytic copper raw foil, and a roughening treatment layer, a catechol-based polymer layer and a silane coupling agent layer which are sequentially laminated on the rough surface of the electrolytic copper raw foil. According to the copper foil, the catechol-based polymer layer is introduced between the roughening treatment layer and the silane coupling agent layer, the catechol-based polymer layer contains rich functional groups such as hydroxyl and amino, the number of attachment sites of a silane coupling agent on the surface of the copper foil is increased, and then the binding force of the silane coupling agent and the copper foil is increased; meanwhile, rich functional groups can also improve the binding force between the copper foil and various base materials, so that the copper foil has higher peel strength under the condition of keeping lower roughness during application.

The invention discloses an FPC high step manufacturing process, which comprises the following steps of: firstly selecting copper plating and then removing a film to carry out whole board copper plating, firstly carrying out local copper electroplating on an area which only needs to be thickened, and covering and protecting a circuit part by a dry film without participating in the copper plating process, so that the copper thickness of a via hole area can be effectively improved on the premise of not excessively increasing the copper thickness of the circuit; after selective plating is completed, copper electroplating is conducted on the whole plate, so that a thin copper layer is evenly plated on the surface of the whole copper foil base material, the step height difference generated during selective copper plating can be effectively reduced, the step gradient can be reduced, and copper surface transition is smoother.

The invention relates to the technical field of copper-clad plate preparation, in particular to a preparation method of a high-frequency flexible copper-clad plate. The preparation method comprises the following steps: taking a mixture of a trifluorochlor oethylene-vinyl ether fluororesin emulsion and a tetrafluoroethylene-perfluoroalkoxy vinyl ether copolymer emulsion as a fluorine-containing emulsion matrix, then adding isopropanol polycarbonate to prepare a composite emulsion, coating two surfaces of a PI film with the composite emulsion to prepare a fluorine-containing polymer layer, and finally preparing the fluorine-containing polymer layer. The fluorine-containing polymer layer has an interface bonding effect, the modified PTFE layer has the effects of reducing dielectric loss and enhancing stability, and the fluorine-containing polymer layer and the modified PTFE layer have a synergistic effect, so that the high-frequency flexible copper-clad plate is prepared. Therefore, the prepared high-frequency copper-clad plate has excellent high-frequency dielectric property, high-strength interface bonding property and excellent mechanical and dimensional stability.

The invention provides a double-sided conduction AMB ceramic substrate and a manufacturing method thereof, and belongs to the technical field of ceramic substrates for power modules. The manufacturing method comprises the following steps: punching holes in a ceramic substrate; filling conductive metal slurry into the holes by using a screen printing machine and sintering at high temperature; brazing materials are printed on the two faces of the ceramic; the copper layer and the ceramic layer are laminated and then subjected to vacuum brazing; manufacturing a circuit; etching the solder layer of the AMB line groove to expose the ceramic; performing surface treatment; laser cutting; and conducting test and inspection. Two-sided conduction is realized through metal slurry hole filling and a high-temperature sintering process, the problem that conduction of an upper copper layer and a lower copper layer of a traditional AMB ceramic substrate cannot be realized is solved, the assembling size of a power module is reduced, the three-dimensional integration requirement of a high-end module is met, meanwhile, the technological process is reasonable, and the production cost is reduced.

The invention relates to a metal-ceramic substrate, to an electronic component comprising a metal-ceramic substrate, and to a method for producing a metal-ceramic substrate. The metal-ceramic substrate comprises: a) a ceramic body which has a main extension plane, b) a metal layer which is connected to the ceramic body in a planar manner, the metal layer having a structuring region which comprises (i) partially solid material and (ii) partially non-solid material, and c) a contact area which is arranged on the metal layer and comprises silver, the structuring region having a geometry in a cross-section through the metal-ceramic substrate perpendicular to the main extension plane, the following requirement being met: S(BCsolid) / S(BCtotal)>60%, wherein: S(BCtotal) represents the total length of the line between points B and C, and S(BCsolid) represents the length of the line between points B and C that intersects the solid material.

The invention discloses a high-temperature-resistant resin glue solution for a copper-clad plate and a preparation method of the high-temperature-resistant resin glue solution, and relates to the technical field of copper-clad plates. The high-temperature-resistant resin glue solution is prepared from the following raw materials in parts by mass: 60 to 80 parts of dicyclopentadiene phenol type epoxy resin, 20 to 40 parts of fluorinated benzoxazine, 10 to 30 parts of dicyclopentadiene phenol type phenolic resin, 5 to 10 parts of hyperbranched polysiloxane, 90 to 100 parts of solvent, 5 to 8 parts of additive and 10 to 20 parts of inorganic filler. Wherein trifluoromethyl and naphthalene rings are introduced into the fluorinated benzoxazine, so that the heat-resistant stability and the dielectric property of the resin glue solution are effectively improved; a copper-clad plate sample prepared from the resin glue solution has a good application effect.

The invention discloses a method for repairing a copper shortage defect of a printed circuit board, which comprises the following steps of: A, carrying out oxidation treatment on the surface of the printed circuit board to form an oxidation protection film on the surface of the printed circuit board; b, determining a copper-deficient defect area on the surface of the printed circuit board, and removing an oxidation protection film and a copper wire in the copper-deficient defect area through laser ablation, so that a base material in the copper-deficient defect area is exposed; c, forming a copper seed layer on the surface of the base material in the copper-less defect area in the step B through laser transfer printing; and D, the printed circuit board in the step C is soaked in an alkaline electroplating solution for electroplating treatment, so that a complete copper wire is generated on the surface of the copper seed layer. The method for repairing the copper shortage defect of the printed circuit board is simple in step and high in operability, low-cost and high-efficiency repairing of the copper shortage defect of the printed circuit board can be effectively achieved, the performance of the printed circuit board cannot be damaged, and the defects in the prior art are overcome.

The invention discloses a production process for preparing a three-dimensional circuit by using laser forming and chemical etching after metallization of a plastic surface, and relates to the technical field of three-dimensional circuit preparation. The method comprises the following steps: S1, carrying out ultrasonic cleaning and oil removal on a plastic base material; s2, performing sand blasting roughening or laser treatment; s3, chemical coarsening is carried out; s4, palladium activation; s5, chemically plating a copper bottom; s6, thickening the circuit by chemical copper plating or electro-coppering; s7, plating a tin or nickel protective layer on the surface of the copper layer; s8, surface metal in a non-circuit area is cut off through laser forming; s9, copper etching is carried out; and S10, surface layer metal is plated again, and passivation hole sealing protection is carried out. According to the method, the material selection range of a three-dimensional circuit is greatly expanded, the processing limitation of a traditional process on a complex circuit structure is broken through, the circuit design requirements in different fields can be met, the process effectively solves the problem of high risk of circuit overflow plating connection when a high-precision circuit is manufactured on the surface of a plastic base material in the past, and the product quality is improved. The precision and the product yield of the three-dimensional circuit are further improved, and the method has a wide application prospect.

The invention discloses an etching compensation structure and method for warping of a thick copper ceramic copper-clad carrier plate, relates to the technical field of ceramic copper-clad carrier plates, and can solve the warping problem of the thick copper ceramic copper-clad carrier plate. The etching compensation method for warping of the thick copper ceramic copper-clad carrier plate comprises a copper-clad carrier plate main body which is warped due to inconsistent material quantities of a double-sided copper plate, and comprises the following steps: S1, covering a convex side surface of the warped copper-clad carrier plate main body with an anti-corrosion blue film; s2, punching film holes, namely punching at least one etching hole array region for etching and compensating warping on the anti-corrosion blue film corresponding to the warping region of the copper-clad carrier plate main body; a plurality of film holes are distributed in a single etching hole array area; and S3, chemical etching: carrying out chemical etching on the warping region of the copper-clad carrier plate main body by etching the hole array region to form an etching compensation structure capable of reducing the material quantity of the copper plate in the warping region of the copper-clad carrier plate main body.

The invention discloses copper-clad plate laminating equipment, and belongs to the technical field of copper-clad plate laminating forming, the copper-clad plate laminating equipment comprises a processing table, the bottom of the processing table is provided with a clamping assembly, the top of the processing table is connected with a guide column, the top of the guide column is connected with a top plate, and the top of the top plate is provided with a driving assembly. The second motor can control the two clamping plates to move oppositely to clamp and fix the base plate, the clamping plates can move downwards synchronously along with the pressing plate when pressed by the pressing plate, and copper-clad plate laminating machining can be conveniently carried out on the base plates of various thicknesses. By arranging the reinforcing assembly, the structural stability of the device can be higher through sliding limiting between a reinforcing block and a reinforcing groove, and the transmission effect of the device can be better by reinforcing the second motor through a positioning sleeve; through the arrangement of the driving assembly, the first motor can drive the two threaded columns to synchronously rotate so that the threaded cylinders can drive the pressing plates to move downwards, and the pressing machining effect can be better through double-lead-screw transmission.

[Problem] To provide a copper-clad laminate capable of simultaneously achieving good volume resistivity in an electroless copper plating layer of a low dielectric resin film and suppression of transmission loss when applied to a flexible circuit board, and a manufacturing method thereof. [Solution] This copper-clad laminate is characterized by including a low dielectric resin film which has a relative dielectric constant of 3.5 or lower and a dielectric loss tangent of 0.008 or lower at a frequency of 10 GHz and an electroless copper plating layer which is laminated on at least one surface of the low dielectric resin film, wherein the electroless copper plating layer has a Ni-content of 0.01 to 1.2 wt%, and the electroless copper plating layer has a volume resistivity of 6.0 µΩ·cm or lower.