U.S. patent application number 10/269265 was filed with the patent office on 2003-05-01 for method for coating metal surfaces.
This patent application is currently assigned to Enthone Inc.. Invention is credited to Franz, Wolf-Dieter.
Application Number | 20030079997 10/269265 |
Document ID | / |
Family ID | 8178944 |
Filed Date | 2003-05-01 |
United States Patent
Application |
20030079997 |
Kind Code |
A1 |
Franz, Wolf-Dieter |
May 1, 2003 |
Method for coating metal surfaces
Abstract
A method for coating a light metal alloy component to form a
protective layer comprising Sn. First, a surface of the light metal
alloy component is cleaned and passivated. A layer comprising Zn is
formed on the surface, and a layer comprising Sn is deposited. An
intermediate layer is preferably deposited between the
Zn-containing layer and the Sn containing layer. The Sn-containing
layer may additionally be varnished.
Inventors: |
Franz, Wolf-Dieter;
(Geretsried, DE) |
Correspondence
Address: |
SENNIGER POWERS LEAVITT AND ROEDEL
ONE METROPOLITAN SQUARE
16TH FLOOR
ST LOUIS
MO
63102
US
|
Assignee: |
Enthone Inc.
|
Family ID: |
8178944 |
Appl. No.: |
10/269265 |
Filed: |
October 11, 2002 |
Current U.S.
Class: |
205/170 ;
205/172; 205/177; 205/181; 205/182; 205/184; 205/210 |
Current CPC
Class: |
C25D 5/42 20130101; C25D
13/20 20130101; C25D 11/34 20130101; C23C 2/02 20130101; C23C
28/023 20130101; C23C 28/025 20130101; C23C 28/00 20130101 |
Class at
Publication: |
205/170 ;
205/172; 205/177; 205/181; 205/182; 205/184; 205/210 |
International
Class: |
C25D 005/10; C25D
005/34 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 11, 2001 |
EP |
01124435.7 |
Claims
What is claimed is:
1. A method for coating a metallic surface comprising: cleaning and
passivating a surface of a light metal alloy component; forming a
first layer on the cleaned and passivated surface wherein the first
layer comprises Zn; and forming a second layer which comprises Sn
such that the first layer is located between the surface of the
light metal alloy component and the second layer.
2. The method according to claim 1 wherein the cleaning and
passivating step comprises: alkaline degreasing the surface of the
light metal alloy component; and performing an acid treatment of
the surface to oxidatively produce a passivation layer on the
surface, the acid treatment comprising contacting the surface with
a solution which is selected from a group consisting of an acidic
solution, a solution comprising the salt of an acid, and
combinations thereof.
3. The method according to claim 2 wherein the light metal alloy
comprises Mg.
4. The method according to claim 3 wherein the acid treatment step
comprises: contacting the surface of the light metal alloy
component with a weak acidic solution; and contacting the surface
with a strong acidic solution which comprises fluoride ions.
5. The method according to claim 4 wherein the light metal alloy
has a Mg composition of at least about 50 weight %.
6. The method according to claim 5 wherein the weak acidic solution
has a pH of from about 3 to about 5.
7. The method according to claim 5 wherein the weak acidic solution
comprises a carboxylic acid and a pyrophosphate.
8. The method according to claim 5 wherein the strong acidic acid
solution has a pH of from about 0.5 to about 2.
9. The method according to claim 5 wherein the strong acidic acid
solution comprises phosphoric acid and ammonium bifluoride.
10. The method according to claim 5 wherein the weak acidic
solution has a pH of from about 3 to about 5 and the strong acidic
acid solution has a pH of from about 0.5 to about 2.
11. The method according to claim 5 wherein the weak acidic
solution comprises a carboxylic acid and a pyrophosphate and
wherein the strong acidic acid solution comprises phosphoric acid
and ammonium bifluoride.
12. The method according to claim 5 wherein the weak acidic
solution has a pH of from about 3 to about 5 and comprises a
carboxylic acid and a pyrophosphate and wherein the strong acidic
acid solution has a pH of from about 0.5 to about 2 and comprises
phosphoric acid and ammonium bifluoride.
13. The method according to claim 2 wherein the light metal alloy
comprises Al.
14. The method according to claim 13 wherein the acid treatment
step comprises contacting the surface of the light metal alloy
component with a strong oxidizing solution.
15. The method according to claim 14 wherein the light metal alloy
has an Al composition of at least about 60 weight %.
16. The method according to claim 15 wherein the strong oxidizing
solution comprises an oxidizer selected from the group consisting
of nitric acid, peroxomonosulfuric acid, and a persulfate
solution.
17. The method according to claim 1 wherein the cleaning and
passivating of the surface of the light metal alloy component
comprises: anodically connecting the surface to an electrical
source; and contacting the surface with a solution which comprises
phosphoric acid and an alcohol.
18. The method according to claim 17 wherein the light metal alloy
comprises a metal selected from the group consisting of Mg, Si, and
combinations thereof.
19. The method according to claim 18 wherein the light metal alloy
has a Mg composition of at least about 50 weight %.
20. The method according to claim 18 wherein the light metal alloy
has a Si composition of at least about 0.1 weight %.
21. The method according to claim 18 wherein the cleaning and
passivating step comprises contacting the anodically connected
surface with a solution that comprises phosphoric acid and fluoride
ions.
22. The method according to claim 17 wherein the light metal alloy
comprises Al.
23. The method according to claim 22 wherein the light metal alloy
has an Al composition of at least about 60 weight %.
24. The method according to claim 22 wherein the cleaning and
passivating step comprises contacting the surface of the light
metal alloy component with an aqueous oxidation agent.
25. The method according to claim 1 wherein the first layer is
formed by chemical metal plating.
26. The method according to claim 1 wherein the first layer further
comprises a metal selected from the group consisting of Cu, Ni, and
combinations thereof.
27. The method according to claim 1 wherein the second layer is
formed by electrolytic deposition.
28. The method according to claim 1 wherein the second layer
further comprises a metal selected from the group consisting of Zn,
Bi, Pb, and combinations thereof.
29. The method according to claim 1 further comprising forming an
intermediate layer such that the intermediate layer is located
between the first layer and the second layer.
30. The method according to claim 29 wherein the intermediate layer
is formed by electrolytic deposition.
31. The method according to claim 29 wherein the intermediate layer
comprises a metal selected from the group consisting of Cu, Ni, and
combinations thereof.
32. The method according to claim 1 further comprising depositing
varnish layer on the second layer wherein the varnish layer
comprises a varnish.
33. The method according to claim 32 wherein the varnish is a
two-component varnish.
34. The method according to claim 32 further comprising performing
a passivating treatment on the second layer prior to depositing the
varnish layer.
35. The method according to claim 34 wherein the passivating
treatment comprises an alkaline anodic oxidation.
36. The method according to claim 35 wherein the passivating
treatment comprises contacting the second layer with a solution
comprising a compounds selected from the group consisting of
phosphates, carbonates, and combinations thereof.
37. The method according to claim 35 wherein the passivating
treatment further comprises a cathodic treatment wherein the second
layer is contacted with a solution comprising hexavalent chromium
ions.
38. The method according to claim 32 further comprising removing a
portion of the varnish layer to expose a portion of the second
layer.
39. The method according to claim 38 wherein the portion of the
varnish layer is removed by bombarding the varnish layer with a
laser beam.
40. The method according to claim 39 wherein the varnish layer is
bombarded by the laser beam at least twice to remove the portion of
the varnish layer.
41. A method for coating a metallic surface comprising: alkaline
degreasing the surface of a light metal alloy component, wherein
the light metal alloy component has a Mg composition of at least
about 50 weight %; performing an acid treatment of the surface to
oxidatively produce a passivation layer on the surface, the acid
treatment comprising: contacting the surface of the light metal
alloy component with a weak acidic solution having a pH of from
about 3 to about 5; and contacting the surface with a strong acidic
solution which has a pH of from about 0.5 to about 2 which
comprises fluoride ions; forming a first layer on the cleaned and
passivated surface wherein the first layer comprises Zn; and
forming a second layer which comprises Sn such that the first layer
is located between the surface of the light metal alloy component
and the second layer.
42. The method according to claim 41 further comprising forming an
intermediate layer such that the intermediate layer is located
between the first layer and the second layer.
43. The method according to claim 42 wherein the intermediate layer
is formed by electrolytic deposition.
44. The method according to claim 42 wherein the intermediate layer
comprises a metal selected from the group consisting of Cu, Ni, and
combinations thereof.
45. A method for coating a metallic surface comprising: contacting
a surface of a light metal alloy component with an aqueous
oxidation agent, wherein the light metal alloy component has an Al
composition of at least about 60 weight %; forming a first layer on
the surface wherein the first layer comprises Zn; and forming a
second layer which comprises Sn such that the first layer is
located between the surface of the light metal alloy component and
the second layer.
46. The method according to claim 45 further comprising forming an
intermediate layer such that the intermediate layer is located
between the first layer and the second layer.
47. The method according to claim 46 wherein the intermediate layer
is formed by electrolytic deposition.
48. The method according to claim 46 wherein the intermediate layer
comprises a metal selected from the group consisting of Cu, Ni, and
combinations thereof.
49. A coating for a light metal alloy comprising: a first layer
comprising Zn wherein the first layer is deposited on a surface of
the light metal alloy component; and a second layer comprising Sn,
wherein the first layer is located between the surface of the light
metal alloy component and the second layer.
50. The coating according to claim 49 wherein the light metal alloy
comprises Mg.
51. The coating according to claim 49 wherein the light metal alloy
comprises Al.
52. The coating according to claim 49 wherein the first layer is
formed by is formed by chemical metal plating.
53. The coating according to claim 49 wherein the first layer
further comprises a metal selected from the group consisting of Cu,
Ni, and combinations thereof.
54. The coating according to claim 49 wherein the second layer is
formed by electrolytic deposition.
55. The coating according to claim 49 wherein the second layer
further comprises a metal selected from the group consisting of Zn,
Bi, Pb, and combinations thereof.
56. The coating according to claim 49 further comprising an
intermediate layer wherein the intermediate layer is located
between the first layer and the second layer.
57. The coating according to claim 56 wherein the intermediate
layer is formed by electrolytic deposition.
58. The coating according to claim 56 wherein the intermediate
layer comprises a metal selected from the group consisting of Cu,
Ni, and combinations thereof.
59. The coating according to claim 49 further comprising a varnish
layer which comprises a varnish wherein the second layer is located
between the first layer and the varnish layer.
Description
BACKGROUND OF THE INVENTION
[0001] This invention relates to a method for coating a surface of
a light metal alloy component. Light metal alloys include, but are
not limited to, alloys that contain Al and/or Mg in an amount that
contributes considerably to determining the chemical properties of
the surface. Because of their low specific gravity, light metal
alloys are of great interest for many different applications in
which both high mechanical stability and the total weight of the
component are important, for example, in aircraft construction,
motor vehicles, or housings for high quality devices. Also, light
metal alloy frame parts lend stability to portable metal telephones
while burdening the user as little as possible. However, light
metal alloys are sensitive to oxidation, so they require surface
treatment to avoid corrosion problems. Typical treatment methods
have the disadvantages of satisfying technical requirements only to
a limited extent, being very costly, or unduly restricting the size
or geometry of the parts that may be treated. Also, such surface
treatments may have a negative effect on the appearance of light
metal alloy components.
SUMMARY OF THE INVENTION
[0002] Among the several objects of the present invention,
therefore, may be noted the provision of a method for coating a
light metal alloy which is effective for corrosion protection. A
further object of the present invention is the provision of a
method of coating a light metal alloy which is capable of coating a
wide variety of surfaces with regard to size and shape. A further
object of the present invention is the provision of a protective
coating for a light metal alloy which has an appealing
appearance.
[0003] Briefly therefore, the present invention is directed to a
method for coating a metallic surface which comprises cleaning and
passivating a surface of a light metal alloy component and forming
a first layer comprising Zn on the surface. A second layer
comprising Sn is formed such that the first layer is located
between the surface and the second layer. The present invention is
further directed to a coating for a light metal alloy comprising a
first layer which comprises Zn and a second layer which comprises
Sn, wherein the first layer is located between the light metal
alloy surface and the second layer.
[0004] Other objects and features of the present invention will be
in part apparent and in part pointed out hereinafter.
BRIEF DESCRIPTION OF THE DRAWING
[0005] FIG. 1 is a view of the internal surface of a diecast Mg
alloy AZ91 chassis for a mobile telephone housing.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0006] In metallurgy and materials science, light-metal alloys are
understood to encompass a variety of metal mixtures comprising
"light metals," such as Al, Be, Mg, and Ti. The most common
light-metal alloys contain Al or Mg. Preferably, the method
according to this invention is performed on light-metal alloys with
a relatively high Al content or those with a relatively high Mg
content.
[0007] A Sn-containing layer enables reliable finishing of a light
metal alloy surface. It has been discovered that a protective layer
comprising Sn adheres well to a light metal alloy surface which has
first been cleaned and passivated and then coated with a
Zn-containing layer.
[0008] Cleaning and Passivating
[0009] An alkaline degreasing of the light metal alloy surface is a
useful initial step for cleaning and passivating. The degreased
surface is preferably treated with a solution which is acidic or
which comprises the salt of an acid to perform some etching of the
light metal alloy surface and which also performs an oxidative
passivation. The term oxidation is generally understood here to
mean a valence electron transition and in particular implies the
formation of oxides like Al.sub.2O.sub.3 and fluorides like
MgF.sub.2.
[0010] In one embodiment, wherein the alloy comprises Mg,
preferably having an Mg fraction of at least about 50 weight %,
especially at least about 80 weight %, the cleaning and passivating
may be performed in two steps. First, the surface is treated with
relatively weak acidic solution having a pH from about 3 to about
5, preferably about 4. Then, the surface is treated with a
relatively strong acidic solution comprising fluoride ions and
having a pH in the range of about 0.5 to about 2, preferably about.
During the etching of the surface, the fluoride ions form a
passivating layer comprising MgF.sub.2. The weak acidic solution
may comprise, for example, carboxylic, citric acid, malic acid,
oxalic acid, lactic acid, a pyrophosphate, and combinations
thereof. The strong acidic solution may comprise, for example, a
mixture of phosphoric acid and ammonium bifluoride.
[0011] In another embodiment, wherein the alloy comprises Al,
preferably having an Al fraction of at least 60 weight %,
especially at least 80 weight %, the treatment is preferably
performed with a highly oxidizing solution that simultaneously
etches the surface and produces a passivating layer comprising
Al.sub.2O.sub.3. Examples of strongly oxidizing solutions are
nitric acid, peroxomonosulfuric acid, and a potassium persulfate
solution.
[0012] Cleaning and passivating may also be performed anodically
with a solution comprising phosphoric acid and an alcohol as
described in co-pending U.S. application Ser. No. 10/176,308, filed
on Jun. 20, 2002, which is herein incorporated by reference in its
entirety. Such cleaning provides effective degreasing and etching
of the surface, and the anodic operation allows for flexible
optimization via parameters such as anodic current density,
voltage, and the like.
[0013] The alcohol may be, for example, methanol, ethanol,
propanol, butanol, a polyhydric alcohol, or derivatives, such as
isopropanol. Diols, polyethers and other alcohols are also useful,
as are mixtures of alcohols. Preferably the alcohol comprises
butanol or isopropanol.
[0014] Preferably, fluoride ions are used as described elsewhere
herein to passivate the surface of a Mn-containing alloy. The
fluoride ions may be in the form of, for example, ammonium
bifluoride, an alkali fluoride, hydrofluoric acid, as well as other
forms. The fluoride ions may be in a solution with the phosphoric
acid, with the alcohol, or with the phosphoric acid and the
alcohol. In a multi-step cleaning and passivation process, the step
performed with fluoride ions is preferably performed last.
[0015] Treatments with fluoride ions, especially the two-step acid
treatments and treatments with phosphoric acid and alcohol, are
also useful when the light metal alloy comprises no or little Mg,
but comprises Si, preferably at least about 0.1 weight %, and more
preferably at least about 0.5, 1 or 2 weight % or higher. The
fluoride ion concentration in this case is dependent upon the Si
concentration.
[0016] The surface treatment with phosphoric acid, alcohol, and
fluoride ions may further comprise an alkaline rinse step,
preferably with an aqueous solution having a pH of at least about
10. However, an alkaline rinse step is less advantageous for a
passivation surface dominated by Al.sub.2O.sub.3.
[0017] Anodic treatment of alloys comprising Al preferably employs
treatment of the surface with an aqueous oxidation agent such as a
persulfate solution or a solution of peroxomonosulfuric acid
(Caro's acid). Oxidation is preferably performed after any fluoride
treatment. An aqueous oxidation step at a pH of less than about 6
may be problematic if the alloy also has a high Mg fraction because
the fluoride passivation can be damaged.
[0018] Useful anodic current densities have a lower limit of about
10, 30 or 50 A/m.sup.2 and an upper limit of about 1000 A/m.sup.2.
Preferably, the light metal alloy surface is cleaned and passivated
at a temperature of from about 10.degree. C. to about 40.degree. C.
The solution used in the anodic cleaning steps comprises phosphoric
acid in an amount which preferably ranges from about 30 to about 90
percent of the solution on a volumetric basis. Within this range of
volume fractions, the phosphoric acid can measure from about 50 to
about 95 percent H.sub.3PO.sub.4 by weight. The solution further
comprises an alcohol and, optionally, fluoride ions. Useful
fluoride solutions have a fluoride content of about 0.1, 0.3 or 0.5
weight % as a lower limit and about 30, 20 or 10 weight % as an
upper limit.
[0019] Coating
[0020] After the cleaning and passivating pretreatments, a layer
comprising Zn and an layer comprising Sb is applied to the light
metal alloy surface. Preferably, the layer comprising Zn chemically
metal plated. This metal plating can additionally contain the
metals Cu and/or Ni. Preferably, the layer comprising Sn is
electrolytically coated. The amount of Sn in this electrolytic
layer is preferably at least about 40 weight %, more preferably at
least about 50 weight %. This layer may also contain, for example,
Zn, Bi and/or Pb in addition to Sb, in order to improve the
corrosion properties.
[0021] The Zn-containing layer is preferably electrolytically
coated with an intermediate layer to protect the Zn-containing
layer from damage by subsequent coating steps, for example, the
electrolytic coating with the Sn-containing layer. The intermediate
layer may comprise Cu and/or Ni. The specific process chosen for
the intermediate coating is matched to the stability of the
Zn-containing metal plating. The intermediate layer is preferably
coated at a pH from about 7 to about 10 because the Zn-containing
layer can be damaged by processes which are too acidic as well as
process which are too alkaline. Processes at pH which may damage
the Zn-containing layer may be desirable or unavoidable in the
production of the Sn-containing layer. Preferred layer thicknesses
for the intermediate layer lie are between about 5 and about 10: m.
Preferred layer thicknesses for the Sn-containing layer are between
about 5 and about 10: m.
[0022] The method according to the present invention provides
stable and permanent electrolytic coatings on light metal alloy
surfaces. Since the method can be carried out with wet chemical and
electrolytic process steps, it is very flexible with regard to the
usable part sizes and geometries and incidentally can be carried
out inexpensively on a large scale. In the above-described
procedures, a metallic conductive surface is achieved, which is
desirable for many applications.
[0023] However, a particular appeal of the invention lies in the
fact that a varnish may additionally be deposited on the
Sn-containing electrolytic layer. This provides far-reaching
freedom with regard to the visual design of the surface. For
example, the varnish can be colored to be opaque or transparent. In
this way many different kinds of decoration effects can be
achieved. It can also have structures, for example, surface
spattering, which can be applied with conventional varnishing
machines in a standard way, in order to give the treated part an
individual visual and tactile appearance. Furthermore, the
varnished surface is characteristically electrically insulating,
which can be desirable, depending on the application. Finally,
better corrosion protection may be afforded by the varnish layer.
Preferably, a two-component varnish is used. One-component
varnishes are useful, but they generally have poorer technical
performance.
[0024] The adhesion of the varnish is improved if the Sn-containing
layer is passivated prior to applying the varnish. Passivation is
preferably performed by alkaline anodic oxidation, for example,
with a solution that contains phosphates and/or carbonates. This
alkaline anodic oxidation can be supplemented by a subsequent
cathodic treatment in a solution of hexavalent chromium, for
example, chromic acid. This results in a coating of the surface
with trivalent chromium. From the standpoint of health and
environment the use of hexavalent chromium is, however, problematic
(although not for the product itself), due to which varnishing the
electrolytic surface that has only been pretreated by alkaline
anodic oxidation is preferable.
[0025] In addition to the advantages already described, the
varnished surface may be subsequently subsequently treated to
return conductivity to partial areas. This can be useful, for
example, in order to apply electrical contacts to the coated
component at specific sites, but where the component is supposed to
remain insulated or coated with varnish for visual appeal or for
protection against chemical and mechanical stress.
[0026] In one embodiment, a laser is used to chip off or evaporate
the varnish at selected parts of the surface and through a
remelting brings these areas to a metallic conductivity. An exposed
Sn-containing layer provides good electrical conductivity and
provides stability for the region from which the varnish has been
removed. Incidentally, laser treatment can also be advantageous in
the case of nonvarnished parts coated in accordance with the
invention in order to give some improvement to the already existing
surface conductivity. Finally, the laser treatment can also be used
if the surface treated in accordance with the invention is provided
with other or additional insulating layers, for instance with
sputtered oxides, nitrides and the like. It is preferable to apply
a flowable metallically conductive substance, for example, an
adhesive or another plastic-based hardening substance that contains
metallically conductive particles, onto the laser-bombarded regions
of the surface within a few hours or a few days. Silver particles
or silver-coated particles are useful. The laser bombardment is
preferably carried out at least two times in order to limit the
thermal stress on the surface, and the laser bombardment be
performed in an atmosphere of air with a conventional apparatus. An
Nd:YAG laser, for example, a 90 W laser, has proven to be suitable.
The process of laser treatment is described in detail in European
Patent Application No. 01124434.0, filed on Oct. 11, 2001 and
titled "Producing metallically conductive surface regions on coated
light metal alloys" and filed on Oct. 11, 2001, which is herein
incorporated by reference in its entirety.
[0027] FIG. 1 is an internal view of a diecast Mg alloy AZ91 frame
part 1, or so-called chassis, of a mobile telephone housing. Frame
part 1 is glued to other metallic or metallically coated housing
parts along a strip 2. It is important that the frame part 1 have
good long-term surface adhesion and a high grade appearance.
Through frequent contact with hands and the resulting simultaneous
effect of salts, weak acids and moisture, and also through the
effects of weather and other circumstances in long-term use, a
surface of frame part 1, not shown, can become unsightly if there
is insufficient coating. Furthermore, corrosion of an inner
surface, not shown, could lead to the formation of particles and
thus to failure of electronic components.
[0028] In the gluing of the parts of a mobile phone, it is
additionally important that the glued parts are bonded to each
other while retaining good electrical conductivity in order to
provide electromagnetic shielding for the telephone. Thus, a stable
coating of the frame part 1 must provide good electrical surface
conductivity along the strip 2 to which glue is applied. The same
is true for flat parts of the indicated support dome 3 for a
circuitboard, which likewise become conductive because of the
necessary mass connection. Other details of the frame part 1 are
not important for understanding of the invention.
[0029] The following examples illustrate the invention.
EXAMPLE
[0030] The frame part 1 is first conventionally degreased by alkali
treatment and treated at pH 4 in a solution with citric acid and
pyrophosphate, followed by passivation at pH 1 in a strongly acidic
solution with phosphoric acid and ammonium bifluoride.
[0031] A chemical conversion layer of Zn and Cu is applied to the
cleaned and passivated surface. Onto this layer a 7: m thick Cu
layer is then be deposited by conventional electrolysis. Then an
electrolytic layer of Sn and Zn is deposited on the electrolytic
layer of Cu. The weight ratio of Zn:Sn is 70:30. The layer
thickness is 8: m.
[0032] This still electrolytically conductive surface is now
prepared for varnishing with an alkaline anodic oxidation in a
phosphate solution. A treatment with hexavalent chromium is not
employed. Instead, a commercial two-component varnish is applied
directly onto the anodized surface and hardened. The surface of the
Mg diecast frame part 1 has the final visual and technical quality
so that it can be varnished with an absolutely transparent color,
so that an attractive appearance results from the metal shining
through the varnish.
[0033] This surface is then treated on the indicated strip 2 and
support domes 3 with a commercial Nd:YAG laser. This laser is Q
switched and has a power of 90 W at a lamp current of about 32 A.
The strip 2 and domes 3 are traced two times, precisely setting
point next to point.
[0034] Empirically, the point spacing, point size and energy per
point can be determined so that a continuous strip of sufficient
width results. The strip width should not be too small, in order to
optimize the electrical contact resistance with the other part of
the housing. On the other hand, the strip width should not be too
great and should be completely covered by the subsequently applied
bead of adhesive (1 mm wide in this example). Also, the coupled
energy per shot should not be unnecessarily high, in order to avoid
heating that is too great at greater depths. By two-fold
bombardment the energy per shot can be kept small. In this case 15
W/mm.sup.2 is used per shot. The laser feed rate in this case is
400 mm/sec.
[0035] Then a bead of silicone glue mixed with silver particles can
be applied to the thus remetallized surface regions 2 and 3, so
that an electrically conductive glueing to another housing part,
not shown, can take place. This other housing part is likewise
metallic or metallically coated and is glued so that it obtains
electrical contact to the adhesive. In this way an electrical
contact to the adhesive is obtained, and a tight and electrically
shielded housing can be produced.
[0036] In view of the above, it will be seen that the several
objects of the invention are achieved.
[0037] As various changes could be made in the above material and
processes without departing from the scope of the invention, it is
intended that all matter contained in the above description be
interpreted as illustrative and not in a limiting sense.
* * * * *