U.S. patent application number 10/885687 was filed with the patent office on 2005-01-27 for method of manufacturing silver flake.
Invention is credited to Wang, Jenn-Shing.
Application Number | 20050016328 10/885687 |
Document ID | / |
Family ID | 34076424 |
Filed Date | 2005-01-27 |
United States Patent
Application |
20050016328 |
Kind Code |
A1 |
Wang, Jenn-Shing |
January 27, 2005 |
Method of manufacturing silver flake
Abstract
A method of manufacturing silver flake, whereby characteristic
of a plating film of providing uniform thickness is utilized, and
material selected for use as a substrate is that which is easily
removed and broken. First, a layer of silver metal is plated on a
surface of the substrate, whereafter such test specimen is crushed
and the substrate removed, or first remove the substrate material
and thereafter crush, and that which remains is silver powder of
extremely uniform thickness. The silver flake thus acquired is
provided with superior thermal and electrical conductivity in a
specific direction.
Inventors: |
Wang, Jenn-Shing; (Yungkang
City, TW) |
Correspondence
Address: |
Far East College
P.O. Box No. 6-57
Junghe, Taipei
235
TW
|
Family ID: |
34076424 |
Appl. No.: |
10/885687 |
Filed: |
July 8, 2004 |
Current U.S.
Class: |
75/354 |
Current CPC
Class: |
B22F 1/0055 20130101;
B22F 1/0007 20130101; B22F 2998/00 20130101; B22F 9/16 20130101;
C23C 18/1657 20130101; B22F 2998/00 20130101; B22F 1/0055 20130101;
C23C 14/0005 20130101; C23C 16/01 20130101; C23C 4/185 20130101;
C25D 3/46 20130101; C23C 18/44 20130101 |
Class at
Publication: |
075/354 |
International
Class: |
B22F 009/02 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 25, 2003 |
TW |
092120301 |
Claims
What is claimed is:
1. A method of manufacturing silver flake comprising steps of: a)
selecting a removable material as a substrate; b) plating a silver
metal layer on the substrate; c) removing the substrate, and
acquire the silver flake of uniform thickness.
2. The method of manufacturing silver flake according to claim 1,
wherein after step b, the following step can be further
implemented: b1. crush the substrate containing the silver metal
layer.
3. The method of manufacturing silver flake according to claim 1,
wherein after step c, the following step can be further
implemented: c2. crush the silver metal layer having already
removed the substrate.
4. The method of manufacturing silver flake according to claim 1,
wherein material of the silver metal layer is silver metal.
5. The method of manufacturing silver flake according to claim 1,
wherein material of the silver metal layer is a silver alloy.
6. The method of manufacturing silver flake according to claim 1,
wherein material of the silver metal layer is metal containing
silver as a constituent.
7. The method of manufacturing silver flake according to claim 1,
wherein material of the substrate comprises metal, ceramic, and
plastic.
Description
BACKGROUND OF THE INVENTION
[0001] (a) Field of the Invention
[0002] The present invention relates to a method of manufacturing
silver flake, whereby material selected for use as a substrate is
that which is easily removed and broken. First, a layer of silver
metal is plated on a surface of the substrate, whereafter such test
specimen is crushed and the substrate removed, or first remove the
substrate material and thereafter crush, and thereby obtain silver
powder of extremely uniform thickness. The silver flake thus
acquired is provided with superior thermal and electrical
conductivity in a specific direction.
[0003] (b) Description of the Prior Art
[0004] Because silver powder is provided with properties including
good conduction of heat and high conduction of electricity, the
silver powder. has extensive application in electronic
encapsulation, electrode contacts, multilayer integrated electronic
components, and so on, and moreover, when heat and electrical
conduction of flake-form silver powder is compared to that of
spheroidal form of silver powder, a considerable difference in
properties of conduction of heat and electricity is found. Due to
fact that collection of the latter spheroidal powder only results
in point contact between spheroidal bodies of the powder, whereas
the former flake-form silver powder amasses by means of directional
accumulation, and apart from point contact between the flakes,
substantial mass-collection of layer upon layer of surfaces is
realized. Furthermore, because points of intersection between the
surfaces of silver flake effectuate larger circulation channels,
phonons and electrons relatively easily transit such surface
contacts therethrough, and thus thermal resistance and electrical
resistance is greatly reduced. The silver flake is thus provided
with superior thermal and electrical conductivity in a specific
direction. For instance, Taiwan patent No. 432085 "Thermal
Conductive Paste Component", utilizes silver flake having
longitudinal length of 10.about.50 microns and thickness of
1.about.5 microns.
[0005] With regard to the aforementioned problems in manufacturing
silver powder, prior Taiwan and international patents or related
publications have disclosed such, including Taiwan patent No.
146827 entitled "Method of Manufacturing Silver Powder", patent No.
490339 entitled "Preparation Method for Micro-Silver Palladium
Alloy Powder", and patent No. 233315 entitled "Preparation Method
for Controlling Surface Area of Silver Powder", all of which
disclose methods for precipitating silver powder out of chemical
solution. Patent No. 261554 entitled "Method of Manufacturing
Silver Powder by Aerosol Decomposition" adopts thermal
decomposition of an unsaturated solution containing silver
compounds, and is similar in concept to that seen in patent No.
458829 entitled "Method of Manufacturing Metal Powder", having a
primary characteristic in utilizing thermal decomposition of
micro-droplets of a metal salt in solution, and at least one
chemical compound can be thermally decomposed to form metallic
powder thereof.
[0006] However, focus of each of the aforementioned patents is in
manufacturing process of manufacturing silver powder, and the
patents do not disclose a method of manufacturing the silver flake.
More importantly, the aforementioned patents are only able to
produce near-spheroidal or irregular-shaped silver powder. An
overall view of methods for producing the metal powder include
reduction method, reducing chemical compound method, vapor
reduction method, chemical vapor deposition method, vapor
condensation thermal decomposition method, liquid phase
precipitation method, electro-analysis method, electrochemical
corrosion method, atomization method and mechanical crushing
method, wherein only the mechanical crushing method is able to
acquire long flake-form powder. However, length of the flake-form
powder is irregular, aspect ratio is excessively large, and shape
of the flakes assumes a lengthways form, which disadvantages
collective compactness of the powder. An additional shortcoming of
excessive bulkiness of the powder reduces utilization value,
particularly when applied in high value-added electronic usage.
[0007] In conclusion, current art is unable to manufacture silver
flake having uniform thickness, whereby uniform thickness of the
silver flake realizes improvement in thermal and electrical
conductivity of the silver flake for application in electronics
industry, and so on.
SUMMARY OF THE INVENTION
[0008] A primary objective of the present invention is to provide a
method of manufacturing silver flake that improves upon the
aforementioned shortcomings, and which is characterized in
utilizing a plating film of uniform thickness and processing that
implements technological measures involving pre-plating and
post-removal.
[0009] Primary steps of the present invention are:
[0010] a. Select a removable material as a substrate.
[0011] b. Plate a silver metal layer on the substrate.
[0012] c. Remove the substrate, and acquire silver flake of uniform
thickness.
[0013] Apart from the aforementioned steps, the present invention
can increase number of processing steps according to requirements
of implementation with the following supplementary steps:
[0014] b1. Crush the substrate containing the silver metal layer
or:
[0015] c2. Crush the silver metal layer having already removed the
substrate.
[0016] The aforementioned substrate can be fabricated from ceramic
(tablet), metal, plastic, and so on.
[0017] The aforementioned measures employed in plating
manufacturing of silver metal layer can be conventional
electroplating, chemical vapor deposition (CVD), physical vapor
deposition (PVD), and so on.
[0018] Furthermore, the silver metal layer can be silver metal,
silver alloy or a metal containing silver as a constituent.
[0019] The silver flake thus acquired by means of the
aforementioned steps is provided with superior thermal and
electrical conductivity in a specific direction.
[0020] Another objective of the present invention is to provide a
processing method for manufacture silver powder having high thermal
conductivity and good electrical conductivity.
[0021] To enable a further understanding of the said objectives and
the technological methods of the invention herein, the brief
description of the drawings below is followed by the detailed
description of the preferred embodiments.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] FIG. 1 shows an electron micrograph of silver flake
manufactured according to the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0023] A first embodiment of the present invention is described
hereinafter:
[0024] 1. Use a tablet as a substrate (the tablet being fabricated
from ceramic material).
[0025] 2. Silver plate the tablet.
[0026] 3. Dispose the tablet having a silver metal plated layer
into a mortar, and grind the tablet, thereby forming fragments
thereof.
[0027] 4. After retrieving the fragments, steep in water and stir,
which thereby effectuates dissolving the tablet.
[0028] 5. Acquire silver powder of uniform thickness.
[0029] Particle size of the aforementioned silver powder can be
regulated by grinding process.
[0030] Material appropriate for the tablet taken as the substrate
in the aforementioned embodiment is that which is easily removed
and broken.
[0031] During the step when the silver metal is being plated on the
tablet, silver is plated on the surface of the tablet by means of
an ion beam deposition film method, having primary function to
effectuate evaporation deposition of the metal silver, and through
assistance of a second ion beam, deposition on the surface of the
tablet is realized, thereby forming the metal silver deposited
film. Procedural method is as follows: procedure is carried out
under a vacuum pressure of 0.00013 Pa with silver of 99.99% purity,
and an argon gas having working pressure of 0.01 Pa; the primary
ion beam formed has an ion energy and beam flow of 700 eV and 10 mA
respectively, moreover, assisting the primary ion beam is an argon
ion beam having the ion energy and beam flow density of 500 eV and
0.0001-0.00001 mA/cm.sup.2 respectively. Growth speed of the silver
film is greater than 0.02 nm/s. Prior to deposition of the
aforementioned tablet, the tablet is necessarily dried to remove
water adsorbed on the surface of the tablet, whereupon silver
plating reaction is proceed with.
[0032] A second embodiment of the present invention is described
hereinafter:
[0033] 1. Use metal as the substrate.
[0034] 2. Implement silver electroplating of the metal
substrate.
[0035] 3. Utilize method of chemical corrosion to remove the
substrate.
[0036] 4. Acquire the silver powder of uniform thickness.
[0037] Technological conditions for plating and manufacture as
employed in the second embodiment are as follows:
[0038] Because silver very easily precipitates out of a cyanide
solution and onto a metal, which results in irregular density of
plating layers, thus, urgent plating processing is necessarily
first implemented, resulting in a great deal of nucleation.
Composition of the cyanide solution is 3.about.6 g/L of silver
cyanide and 120.about.150 g/L of sodium cyanide, to supplement with
high-current density the cyanide solution is thereupon disposed
within an electroplating solution, composition of which is
45.about.50 g/L of silver cyanide (AgCN), 45.about.50 g/L of
ionized potassium cyanide (KCN), 10.about.14 g/L of potassium
hydroxide (KOH), 45.about.80 g/L of potassium carbonate
(K.sub.2CO.sub.3), and 40.about.60 g/L of potassium nitrate
(KNO.sub.3). Electroplating current density (stirring) is 8
A/dm.sup.2, and working temperature is 38.about.45.degree. C.
[0039] The method of chemical corrosion is utilized to remove the
substrate of the second embodiment, and the metal substrate chosen
is one provided with corrosiveness, whereas a chemical solvent
having non-corrosive properties towards silver metal is utilized to
implement corroding effect, which can thus achieve objective of
removing the substrate and retrieving the silver flake. In the
aforementioned embodiment, the step involving removing the tablet
by means of chemical corrosion utilizes aluminum metal as the
substrate, and the chemical solvent is 30 wt % sodium hydroxide
solution. The aluminum substrate having surface plated with the
silver film is disposed into the sodium hydroxide solution,
whereupon the aluminum completely dissolves leaving the silver
film.
[0040] A third embodiment of the present invention is described
hereinafter:
[0041] 1. Use glass (ceramic material) as the substrate.
[0042] 2. Utilize method of solution deposition to implement silver
plating surface of the glass (ceramic).
[0043] 3. Remove the substrate by means of method of thermal
stress.
[0044] 4. Acquire the silver powder of uniform thickness.
[0045] Technological conditions for plating and manufacture as
employed in the third embodiment are as follows:
[0046] Settle out silver ions from a metal silver compound by means
of a reducing agent effect, which reduces the silver ions and
deposits the silver on the surface of the glass substrate. Actual
method employed is: add 50 g of silver nitrate (AgNO.sub.3) to 2
liters of water, add 50 g of potassium hydroxide (KOH) to 2 liters
of water, add 80 g of sugar to 0.8 liters of water, permeate 3.5 ml
of nitric acid (HNO.sub.3) in 100 ml of water, and mix all together
in a 16:8:1 ratio respectively. Thereafter add ammonium hydroxide
(NH.sub.4OH) to the silver nitrate (AgNO.sub.3) and the potassium
hydroxide (KOH) solution, thereby forming a non-sediment solution,
whereupon nitric acid (HNO.sub.3) is further poured in, whence a
silver plating reaction commences.
[0047] The method of thermal stress is utilized to remove the
substrate of the third embodiment. Regarding heating, because
different substances are provided with different coefficients of
expansion, thus cold contraction and hot expansion produced by
heating and cooling can be utilized to realize removal of the
silver powder from the substrate, thereby forming flakes
thereof.
[0048] A fourth embodiment of the present invention utilizes a
method of plastic electroplating to silver plate on ABS plastic
(Acrylonitrile Butadiene Styrene plastic), whereby a procedure
undertaken to realize such is as follows:
[0049] 1. Alkaline cleaning of the substrate: Utilize an alkaline
to clean the substrate, thereby effectuating removal of
contamination from the surface of the substrate, including
contamination from being subject to dust in air, grease and
fingerprints.
[0050] 2. Etching: Etching is implemented by means of 90 g/L of
strongly oxidized potassium dichromate (K.sub.2Cr.sub.2O.sub.7) and
600 ml/L of sulfuric acid (H.sub.2SO.sub.4), thus enabling the ABS
(Acrylonitrile Butadiene Styrene) plastic surface to become
hydrophilic therewith. Working temperature is 60-70.degree. C., and
time required is 5-10 minutes. However, too short a time will
result in local non-plating, whereas too long a time will result in
an inferior surface, which reduces adhesive strength of the plating
film.
[0051] 3. Neutralizing: Remove six valence chromium and chromous
salts remnants left from etching, which thereupon improves
post-manufacturing agent processing of adsorption condition of the
surface of the plastic.
[0052] 4. Catalysis: Subdivide to complete sensitizing and
nucleation, wherein sensitizing is undertaken with 20 g/L of tin
chloride (SnCl.sub.2), 40 mls of hydrochloric acid (HCl) at
20-25.degree. C., and time required is 1-3 minutes, which thereby
enables the reducing agent to adsorb onto the surface. After
reducing, a post-nucleating agent reaction is implemented to form a
metallic state. Formulation for nucleation is 0.25 g/L of palladium
chloride (PdCl.sub.2), 2.5 ml/L of hydrochloric acid (HCl) at
20-40.degree. C., and time required is 0.5-1 minutes. The
aforementioned two steps can be executed together. However, the
above formulation would thus have to be amended.
[0053] 5. Acceleration processing: Diluted acid or diluted alkali
is utilized to remove residue tin compounds, and palladium is
thereby completely exposed, thus enhancing the catalysis function.
Working temperature is 20-50.degree. C., and time required is 2-10
minutes.
[0054] 6. Proceed with electroless silver plating: A plating bath
is first prepared having components (A) 60 ml/L of silver nitrate
(AgNO.sub.3), 60 ml/L of ammonium hydroxide (NH.sub.40H) (28%
concentration), and (B) 210 ml/L of formaldehyde HCHO (37%
concentration). Only upon starting electroplating is one portion of
solution (B) added to five portions of solution (A). Upon needing
to deploy the plating bath, the silver nitrate is first dissolved
in approximately two thirds pure water, whereafter, ammonia is
extremely slowly added to solution and mixed, and an object to be
plated is thereupon placed into the solution.
[0055] 7. Remove the substrate: A heating method is utilized to
thereby realize melting of the substrate and acquiring of silver
flake thereof or a chemical solvent is employed to erode away the
substrate, and the silver flake can analogously be procured
thereof.
[0056] It is of course to be understood that the embodiments
described herein is merely illustrative of the principles of the
invention and that a wide variety of modifications thereto may be
effected by persons skilled in the art without departing from the
spirit and scope of the invention as set forth in the following
claims.
* * * * *