FR2498125A1 - COPPER COATED LAMINATE AND METHOD OF MANUFACTURE - Google Patents

Abstract

LAMINATE IN WHICH THE COPPER FILM ADHESES DIRECTLY TO THE BACKING SHEET. IT INCLUDES A SUPPORT SHEET 18 IN UNCOATED METAL AND A FINE GRAIN COPPER FILM 14 DEPOSITED IN THE STEAM PHASE, IN DIRECT CONTACT WITH THE SURFACE OF THE SUPPORT SHEET AND ADHESIVE TO IT WITH A PELING RESISTANCE INCLUDED BETWEEN APPROXIMATELY 0.876 AND APPROXIMATELY 3.502NCM. APPLICATION TO THE MANUFACTURING OF PLATES FOR PRINTED CIRCUITS.

Description

The present invention relates, in a manner

  generally, stratified materials and, more

  a new copper-clad laminate

  useful for the production of high-resolution printed circuit boards and a new

  assigned to manufacture these products.

  This invention is related to the invention described and claimed in the French patent application

  No. 81 15 979. Fine-grained copper surfaces, virtually

  pin-free and extremely smooth copper-clad laminates produced by the process of the invention of this application

  important characteristics of the products obtained in accordance

  to the recommended implementation of this invention.

tion.

  The invention described and claimed here is also

  related to that described and claimed in the

  French Patent Application No. 81 17828.

  As used herein and in the claims

  appended, the term "support" characterizes a material of aluminum sheet of calibrated thickness allowing it to undergo a transformation cat and to be wound up to be stored or transported, it also characterizes sheet materials of other metals such as copper as well as plastics, such as duPont's commercial products, known as MYLAR and KAPTON, and other polymeric organic materials of similar flexibility. All these materials are able to withstand the processing temperatures incurred in this

  invention and exhibit the desired temperature resistance

  of copper film deposition and the properties of inactivated

  ability and ability to link with cooking films.

  necessary to preserve the integrity of the combination

  his film-support sheet during transformations

  follow and its attachment to the substrate and to allow

  the mechanical tearing of the support sheet without

damage the copper film.

  The adjective "ultra-thin" characterizes

  thicknesses less than about 16 micrometers.

  The terms "film" and "leaf" mean,

  respectively, in the same context an ultra-thin coating

  thin and the combination of this coating and one or more ultra-thin coatings of another metal or a

other material.

  The term "vapor phase deposition" covers spraying, physical evaporation (i.e.

  electronic beam evaporation processes, evaporation

  inductive and / or resistive poration), chemical deposition in

vapor phase and ionic deposition.

  As used in this description and

  in the appended claims, the term "substrate"

  characterizes the part of the laminate product coated with

  or any other manufactured part of that invention

  which serves as a physical support for the film or foil, and which is advantageously constituted by a

  glass-epoxy element in a hardened pre-impregnated form

  when in contact with copper foil or other metal.

  Among other materials that can be used

  to this end, without limiting it, what

  in the trade of "phenotype papers-resins"

  which are products consisting of sheets of paper impregnated with a hardenable resin to form

  an adhesive bond between the substrate and the metal foil

  laminate. Other materials of this type can also be mentioned polyimides and polyester resins.

  So far the leaves for stratum have been

  copper cladding for use in the production of

  printed circuit boards, essentially by electrolytic deposition. The many advantages of this process, among which we can mention the speed of production,

  economy, and the existence of a very advanced technology.

  are counterbalanced by major disadvantages. Among these disadvantages,

  the very important one, which is the difficulty of

  leaves less than 16 micrometers thick without pinholes, as well as the impact on

  the environment of the practice of electrolytic deposition.

  Although some of the disadvantages of pinholes can be overcome by electrolytically depositing copper on the surface of

  aluminum support prepared in a particular way,

  according to the U.S. Patent No 3 969 199, it is at the cost of greater complexity and costs of transformation.

higher.

  The disadvantages of the prior art can be overcome

  using the described and claimed inventions

  in the French patent applications cited above.

  It can now also be remedied in another way

  again according to the process of the present invention.

  So, instead of coating the surface of the support with a peel agent before depositing the copper film, the copper is deposited directly on the bare surface of the support

  in a way that will then allow the separation not

  supporter of the support film. In other words, this invention allows the removal of the peel agent layer while retaining its function. This is achieved by adjusting the degree of bonding of the film obtained during the deposition of the copper on the support. This invention is therefore based on the new idea of depositing copper in the vapor phase under conditions of roughness, cleanliness and temperature of the surface of the support, making it possible to obtain a high quality copper film virtually free of holes. pin, which is related to the support, but which one can

  remove it by application of a peeling force or

  acceptable. As a general rule, in accordance with

  As a result, the surface of the support will be clean and free of adhering dirt and oil which would interfere with a good bond or contaminate the resulting copper film, it will be relatively smooth and free of gross physical irregularities. In addition, the temperature of the surface of the support will, according to this invention, be between about 1000C and about 2500C so that sufficiently strong bonds are formed but not too much

  between the copper film and the support.

  During the implementation of

  this invention that electron beam evaporation

  was a method of implementing the step

  particularly satisfactory copper deposit, the tempera-

  the surface of the support being easily adjusted

  different ways under these conditions, and a

  film of desired thickness quickly becoming uniform

  attached to the surface of the support, as desired.

  However, consideration was also given to the possibility of

  copper ion film, which presupposes

  the polarization of the support and, if desired, the introduction

  inert gas such as argon in copper vapor to cause the necessary ionization effect. Again, in the case of ionic deposition, the temperature of

  the surface of the support would be easily adjustable by

  its alternatives. It has also been envisaged that a method of

  Inductive evaporation (RF) of copper instead of the electron beam evaporation process as a process for the production of copper vapor required for

  physical vapor deposition, and again the temperature

  the surface of the support would be easily adjustable.

  If, however, spraying is used as a deposit method in the practice of this invention, it will be necessary to take certain special measures.

  to eliminate heat so as to maintain the temperature

  of the surface of the support in the range to limit the development of the bond strength to the

  value that has been found critical for the new results

  states and advantages of this invention.

  It will be understood by those skilled in the art that regardless of the manner in which the invention is used to produce the copper film on the surface of the support, it is possible, in order to produce the laminated element, to use the one or

2498 125

  the other of the methods described and claimed in the French patent applications cited above. We are

  refer to the descriptions of each of the two requests

  the stages of production of the laminates, each of the distinct steps of each of the different processes being described in general terms and

particular in these descriptions.

  In short, the process of this invention therefore comprises the steps of forming a copper film on a support by vapor phase copper deposition directly on the surface of the support at a temperature of from about 1000 ° C to about 250 ° C. a substrate-bonding layer on the copper film, making a laminate with the resulting element and a substrate so as to create a strong adhesion between the element and the substrate, and finally removing support for

  retain the substrate to which the element adheres. accordance

  In accordance with the invention of French Patent Application No. 81 15 979, the substrate-binding layer is an electrolytically deposited film which is preferably a copper film, and which in any case is produced in a to present a nodular dendritic surface promoting the bond with the substrate. Alternatively, the

  substrate bonding layer may be an ultra-thin film

  electrolytically deposited zinc, aluminum, tin or chromium, covered with an ultra-thin film of silicon dioxide or aluminum oxide, as indicated

  in the French patent application No. 81 17 828.

  The following description refers to the figures

  FIG. 1 is a diagrammatic representation of a sectional view of a laminate product of the invention at an intermediate stage of its production; Figure 2, a view similar to that of Figure 1 of the product of the invention before the removal of the aluminum support sheet; FIG. 3, a view similar to that of FIG. 1, illustrating the step of removing the support sheet by tearing off, by application of a force of

coat from 0.876 to 3.502 N / cm.

  As shown in FIG. 3, the product 10 of this invention, as it may be in the form of an article of commerce intended to be used, for example, at the end of manufacture, for the production of platelets printed circuit board comprises a substrate 12 to which is bonded a vapor-deposited copper film 14 bonded to the substrate by a bonding layer 16

  electrolytically deposited or otherwise formed.

  It also includes a support sheet 18, which

  aluminum or aluminum alloy on which is formed the vapor-deposited copper film at

  course of the new key step in the process of this invention.

  tion. As also shown in Figure 1, the step

  the process to which the principal

  The features and advantages of the present invention as

  described above, is the initial training stage.

  of the copper film 14 on the carrier sheet by vapor deposition under conditions which allow

  their final separation by peeling or peeling by application

  cation of a force of intensity sufficiently small not to damage or destroy the finished laminate produced, for example by tearing or breaking the copper film on which one must ultimately form a printed circuit by a semi-additive or subtractive technique, by

example.

  The method of the present invention, in its recommended form, comprises as a first step the cleaning of the aluminum support sheet. It is a product made of uncoated sheet of which the surface can be specially prepared, for example by cleaning, or which can be used in the state in which it is produced during manufacture. normal commercial of the metal sheet. In all cases, the aluminum or aluminum alloy sheet will conventionally be covered with a coating of oxide formed naturally of a little less than about 50 Angstroms thick, and in the most cases currents, from 10 to Angstr5ms thick. The carrier sheet preferably has a thickness of 0.025 to 0.178 mm, but may be a little thinner or a little thicker, if desired, and will have a better square root surface finish than 0.203 micron. The

  cleaning of the leaf as found on the

  when it has just been produced by a commercial rolling operation is essential to obtain a uniform laminate product since it is necessary that the copper film applied to the aluminum foil during the first step of the deposition process is bonded, although relatively weakly, to the supPort sheet, so that the assembly retains its integrity in the subsequent processing steps. Cleaning at the

  vapor with liquid Freon or other suitable material

  The present invention may be useful, but plasma etching or ozone cleaning are preferred and known techniques for general cleaning purposes where a high degree of surface cleanliness is required.

reproducible way.

  When the surface of the support sheet has been prepared, copper is applied by a vapor deposition technique, as previously described, and a copper film is formed on the surface of the support sheet.

  clean surface of the aluminum backing sheet.

  According to the most preferred embodiment, an electronic beam device is used, and in all cases, this step is carried out so as to produce a coating that can be ultra-thin or a little thicker, its thickness being able to up to 25 micrometers, if desired. Filed this way,

  or by another method, for example using a

  Induced by induction heating or ionic deposition, the copper film will have a particle size of G, W ''.

2498 125

  a few hundred to a few thousand Angstroms, as opposed to the much larger particle size of copper films deposited by electroplating, of the order of

  one to two micrometers at least. To obtain this result,

  tat, the surface of the aluminum support foil is maintained throughout the duration of the deposition operation

  on which the copper film is deposited at a temperature of

  ture between about 100 and 2500C. It was found that the use of a slightly higher temperature caused

  the formation between the copper film and the sheet of

  aluminum port of a sufficiently strong bond to make the peeling or mechanical tearing of the film of the

  difficult or impossible sheet without damage to the film.

  On the other hand, it has been found that the use of temperature

  a little lower, the formation of a link

  it does not preserve the integrity of the whole

  copper film-aluminum support during the steps

subsequent processing.

  When the formation of the copper film by a

  vapor deposition technique is complete, the whole

  result is ready for the next step of the process.

  This step involves the preparation of the copper film for

  attach it to a substrate and can be used

  according to the process described and claimed in French Patent Application No. 81 15 979 cited above, or

  that described and claimed in the French patent application

  It will be understood, however, that it will be possible to treat it differently, by an existing or future process, to obtain the desired final result as regards the binding of the copper film to the final substrate with which it will have to form. a laminate, for use in the production of printed circuit boards or for other applications. Reference is therefore made to the part of the French patent application No. 81 15 979 concerning the preparation of the surface of the copper film and the subsequent steps of bonding to the substrate. We will refer to the

  same way to the corresponding part of the description

  French Patent Application No. 81 17 828. There is currently no preference for either of these methods in the practice of the invention because they are also safe and comparatively economical in their usage. The binding to the substrate is then carried out by one of the methods referred to or by another method chosen to form the product.

  finished and it remains for the end user to remove

  wrap the backing sheet by peeling it or tearing it mechanically. This is the most recommended method to remove the support but it will be understood that we may have the choice, in some cases, to use alternatively

  chemical means, namely of dissolution. We always

  the peeling or peeling in the simplest possible mechanical manner and it is sufficient to apply a limited, non-destructive peel force with respect to the integrity of the copper film which constitutes the active part of the laminate directly. concerned in the production of the printed circuit board or for a

  another use of the same type of laminate.

EXAMPLE I

  Three aluminum support sheets were cleaned

  0.076 mm, in the raw state of rolling, by

  Plasma was applied to a 16 cm x 10.16 cm (and 6.35 mm thick) glass plate and a thermocouple was attached to one of the edges of the sheet in all directions. case. Using two 15.24 cm quartz lamps placed on each side of the assembly in a vacuum chamber, the temperature of the

  support sheet at 300 ° C and maintained there, the pressure

  sion being lowered into the chamber at 10.64 × 10 12 daN / mm 2.

  It was then vapor deposited, using a

  positive electron beam, a copper film of

  5 micrometers on the apparent surface of the sheet of

  luminium. During the 10 minutes when the copper melted, the pressure in the vacuum chamber was 4.79 × 10 11 daN / mm 2. Then, during the evaporation step it was 7.98 × 10 11 daN / mm 2. The temperature of the aluminum foil was maintained at 50 ° C. for 45 minutes during the deposition step of the process. It was found that the peel strength of the copper film of one of the test pieces was 5.323 N / cm. We trained

  nodular structures on the surface of the second

  in a bath of copper sulphate for 30 seconds.

  0.15 A / cm 2 and pressed against an FR4 glass-epoxy plate by applying a pressure of 0.10 daN / mm 2 and a temperature of 1660C for 35 minutes as described in the French patent application.

  No 81 17 828 mentioned above. The peel test practically

  on the carrier sheet by cutting a 3.175 mm band from the edge resulted in tearing off the copper film from the plate and thus destroying the laminate for use in the production of platelets.

  circuit boards for which it was intended.

  The third specimen was assembled with the substrate which was then heated for 45 minutes at 3000 ° C. with the consequence that the copper was annealed with aluminum forming a composite which could not be separated cleanly by application. peeling or pulling forces.

EXAMPLE II

  In another experiment similar to that of

  example I, except that the sheet of paper had been cleaned

  steaming with Freon, the temperature was maintained

  aluminum-copper foil at about 1200C

  during the entire duration of the copper deposit. On testing, the peel strength of the copper film was found to be 2.802 N / cm. We have implemented this test in the way

  described in Example I by assembling the sheet of

  port coated with the copper film with the tie layer and the substrate, as described in Example I.

  then implemented the test to determine the resistance

  peeled on the 3.175 mm strip cut from the test piece and a test device was

2498 125

  peel as in example I to measure the resistance

peeling.

EXAMPLE III

  In another example similar to that of Example II, which used a freoned aluminum backing sheet with Freon 0.076 mm thick, the other film deposition conditions were as follows:

  copper and the production of the laminate product with the

  the same, it was found during a test conducted in the manner described above that the resistance

  peeling of the laminate product was zero. A pre-test

  limb of peel strength leads on the film before its assembly with the substrate also provided a

null value.

EXAMPLE IV

  In another experiment similar to that of Example II, except that the temperature of the support sheet was maintained at 250 ° C throughout the copper film deposition, it was found, during the course of test of the final laminated element with the substrate that the peel strength was between 1.541 and

1.751 N / cm.

EXAMPLE V

  Another experiment similar to that of Example II led to coat resistances of

  2,451 N / cm and 3,082 N / cm when maintaining the temperature

  aluminum support foil at 260 ° C. for the duration of the deposition of the copper film, the

  other conditions remaining unchanged.

EXAMPLE VI

  In another experiment similar to that of Example V, except that the temperature of the support was maintained at 240 ° C. throughout the deposition period, a peel strength was measured, in a case of 0.420 N / sec. cm, in another case of 0.840 N / cm and in a third case of

1.401 N / cm.

  In another recent experiment, a 0.3 micron vapor-deposited copper film was prepared on uncleaned raw aluminum foil at room temperature. It has been found that resistance to

peeling of this film was void.

  It is evident from the results obtained in the experiments described above that the new results and advantages of this invention can be achieved under certain conditions which are very critical. It is therefore

  clear that the temperature at which the sur-

  The face of the support sheet during the deposition of the copper film is of vital importance to the strength of the bond formed between the copper film and the aluminum support. In addition, it is evident that the nature of the surface of the aluminum support sheet on which the copper film is deposited has a significant bearing on the strength of this bond. Finally, it is clear from these experiences that the cleanliness of the surface of the aluminum backing sheet on

  which the copper film is formed has an important

  aunt on the peel strength of the bond, and of course, may also be of importance with respect to the contamination of the resulting copper film and the value and usefulness of the final laminate product. It is recommended to use as a cleaning method, plasma etching known in the art. The Freon Evaporation Process and Other Steam Cleaning Processes

  give varying results as shown by the data

  have been reported above, and it is therefore not approved for use in the most

this invention.

Claims (13)

  1. Laminated product coated with copper, characterized   in that it comprises a support sheet (18) of uncoated metal and a fine-grained copper film (14) which is de-vaporised in the vapor phase, in direct contact with the surface of the   support sheet and adhering thereto with a resistance   peel strength from about 0.876 to about 3.502 N / cm.   2. Laminate product according to claim 1, characterized in that the support sheet (18) is made of non-anodized raw rolling aluminum.   and is covered, therefore, by a natural coating   oxide oxide of less than about 50 Angstroms thick.   3. Laminate product according to claim 1,   characterized in that the support sheet is polymeric organic matter.   4. The laminate product according to claim 1,   characterized in that the support sheet is aluminum   rolled nium whose surface has a surface finish   better in mean square value than 0.203 micro-   metre. Layered product according to claim 4, characterized in that the carrier sheet has been cleaned. 6. A method of manufacturing a copper-coated laminate, characterized in that it comprises the steps of: forming a copper film (14) on a supocrt sheet (18) by vapor deposition of the copper directly   on the surface of the support, keeping the surface of the sup-   port at a temperature between about 1000C and about 2500C; depositing a tie layer (16) on a substrate (12) on the copper film; forming a laminate with the resultant foil member and a substrate so as to create a strong adhesion between the element and the substrate, and   removal of the support foil for   serve the substrate to which the element adheres.   7. Method according to claim 6, characterized in that one carries out the step of removing the support sheet by physical tearing of the element to   sheet of the support sheet by application   a peel force of about 0.876   and 3.502 N / cm at the foil element.   8. Process according to claim 6, characterized in that the copper film is produced by evaporation. by electron beam.   9. Method according to claim 6, characterized   in that the copper film is formed by ionic deposition.   10. Process according to claim 6, characterized   in that the carrier sheet is an aluminum foil   rolling stock coated with a thick oxide film   between 10 and 20 Angstroms, in that one   forms the copper film by electrical beam evaporation   tronic, and in that it includes the step of electrolytically treating the copper film to produce a sheet   in order to increase the adhesion to the substrate.   11. The method of claim 8, characterized in that it comprises the steps of vapor deposition of a zinc film on a copper film and deposition in   vapor phase of a silica film on the zinc film.   12. Method according to claim 6, characterized   in that the step of depositing the bonding layer on the substrate   trat includes the electrolytic deposition of copper under the   forms a very irregular coating on the copper film.   13. The method of claim 6, characterized in that the deposition of the substrate bonding layer comprises the vapor deposition of an ultra-thin film of a metal selected from the group consisting of zinc, aluminum , tin and chromium on the copper film and the vapor phase deposition of an ultra-thin film of an oxide selected from the group consisting of silicon dioxide   and the aluminum oxide on the resulting metal sheet.