DE4438791C2 - Substrate provided with metallized polyimide surfaces - Google Patents

Description

The invention relates to a substrate with polyimide surfaces, coated with resistant to aqueous-alkaline solutions adherent metal layers.

Polyimide has long been used as substrate material in the Elek electronics industry for the production of printed circuit boards, Hy bridging circuits, semiconductor carriers (chip carriers, multi-chip Modules) and other components used. This material has over conventional materials, such as Epoxy resins, considerable advantages. For example its thermal resistance higher, so that the Längenaus Strain of the material under thermal stress is lower than with conventional materials. Furthermore, have polyimide substrate over better electrical insulation values.  

For the production of polyimide laminates, for example for the Circuit board manufacturing has been mostly used in the past used with copper foils laminated polyimide films. From the Copper layers are the conductor tracks mostly by etching processes educated. For this purpose, process techniques are used, the are widely described in the literature (for example, in Handbuch der Leiterplattentechnik, Ed. G. Herrmann, Volume 2, Eugen G. Leuze Verlag, Saulgau 1991). Such methods Although they are basically for the production of printed circuit boards suitable, however, the width of the finest with such Techniques reproducible manufacturable conductor tracks in the area of about 100 microns.

Finer conductor tracks are possibly produced by that no laminates with copper foils on the surface be used as starting materials. The conductor cables who in this case by metal deposition directly on the Surfaces formed. By sputtering or metal evaporation or adhesive-free Po produced by means of chemical methods Lyimidsubstrate have become in the PCB production so far can not enforce. Especially when used Chemical methods, the disadvantage of larger water occurs Inclusion of polyimide over other polymers in the Vor the reason. It has been shown, for example, that the Haftfe Stability of completely flat on polyimide films de-energized and ele kroolytically deposited copper layers to Polyimidober surface during thermal treatment, for example during soldering, significantly reduced or canceled altogether. To that Appearance of bubble-shaped lifts in the thermal To avoid treatment is generally suggested that coated polyimide films after the deposition to anneal.  

However, the tempering treatment is not enough, the Auftre to avoid bubbles when bilateral and completely flat provided with copper layers Polyimidfolien a thermi treatment. In this case, the trapped moisture from chemical metallization tion process, no longer results in the tempering treatment escape, so that they ex when exothermic treatment popping out of the polyimide film and the copper coating lifts off the polyimide surface.

For the above reasons, other methods have become adherent metallization of polyimide substrates developed.

Because of the requirement, adequate adhesion of the deposited metal layers also during and after one thermal stress to reach the substrates have been Vacuum method used for metallization. The metal ab divorce by decomposition of volatile metal compounds with The glow discharge represents a superior process example. In DE 35 10 982 A1, such a method for Production of electrically conductive structures on non-conductors, for example, polyimide films, by deposition of metallic Films on the non-conductor surfaces by decomposition metal organic compounds in a glow discharge zone open beard. The deposited metal films are preferably used as catalytically active seed layers for the subsequent electroless Metallization of the surfaces.

In DE 37 44 062 A1 discloses a method for producing metal Lischer structures on fluorine polymers or thermoplastic Plastics by decomposition of organometallic compounds  in a glow discharge and subsequent electroless metalli described sierung.

In DE 38 06 587 A1 discloses a method for producing metal Lischer structures on polyimide by decomposition metallorga nischer compounds in a glow discharge and subsequent electroless metallization described.

With these methods, it is possible to adhere firmly adhering metal on polyimide surfaces when on the first further metal produced by glow discharge metal layer tallschichten from baths for electroless and electrolytic Metallization are deposited. In the mentioned documents The prior art is for the electroless Metalli tion usual copper or nickel baths indicated.

It has now been found that a sufficient Haftfe Strength of the deposited metal layers on the polyimide surface is then not given when the coated sub strat after the required tempering treatment and before or during the test to determine the adhesion comes in contact with aqueous alkaline solutions. When aqueous-alkaline solutions come, for example, the Ent winding and stripping solutions in the structuring process Photoresists are considering ladder structures from the whole to form flat deposited metal layers. One after The heat treatment can be done by contact with the aqueous-alkaline solution caused reduction of detention strength no longer undo.

The present invention is therefore the problem reason to avoid the disadvantages of the prior art  and to find a substrate having polyimide surfaces with which it succeeds, adherent metal layers on the Polyimidober to separate surfaces, in particular very fine ladder To produce tensile structures and in which the adhesion of the Metal layers on the surfaces by after their deposition contact with aqueous alkaline solution is impaired.

The problem is solved by claim 1. Preferred Ausfüh Forms are given in the dependent claims.

Such a substrate may be used in a process with the following essential process steps are generated:

• - Forming a first metal layer in direct Kon with the polyimide surfaces by decomposition Volatile metal compounds by glimment charge,
• Forming a second metal layer on the first Metal layer of a nickel / boron alloy layer or a nickel / phosphorus alloy layer with about 4 wt .-% phosphorus or a pal Ladiumschicht by electroless deposition of a acidic or neutral set metallization bath.

The deposited by glow discharge first metal layer has unusual properties: The deposition parameters are smooth and high-gloss zend. By rubbing on the surface of these layers can  however, a part of the metal film is easily removed. the This proportion of the layer has a low adhesive strength Polyimide surface on. Using high-resolution electronmi microscopy (Scanning Electron Microscopy, Transmission Electro nenmikroskopie) could be found that the abge different layer a relatively compact structure of kugelför Miges has particles that are obvious to each other have only low binding forces. Obviously alone due to its small layer thickness, this metal layer in a treatment with aqueous-alkaline solutions not destroyed.

By depositing a second layer of a nickel / boron or a nickel / phosphorus alloy containing about 4% by weight Phosphorus or palladium from an acidic or neutral Lö For electroless plating, this upper may be loose Proportion of the first metal layer to be solidified, but without the adhesion between the adherent parts of the first metal layer and the polyimide surface to impress pregnant. It is formed a compact metal structure, so that the formed layer composite against a chemical handle becomes resistant by aqueous-alkaline solutions. When using the acidic or neutral baths results From this, further, that the bond between the separated NEN metal layers and the polyimide surface by contact is not reduced with aqueous-alkaline solutions. because In addition, polyimide takes in the chemical deposition significantly less moisture than in the known Ver drive, so that after treatment also less hydroxyl ions remain in the material, especially in thermal Loading of the substrate hydrolytic act and the Haftver could weaken the federal government.  

It was found that the best results with baths for electroless metallization with a pH between 2 and 6 can be achieved.

As Metallisierungsbäder come to electroless deposition in particular nickel, copper, cobalt, palladium or Le gierungsbäder these metals into consideration.

Particularly suitable is a nickel / boron alloy layer as second metal layer, since this to produce the Metallstruk easily etched from the whole-area metal layer that can.

In another preferred embodiment, the second Metal layer from a very thin palladium de-energized divorced, which can be easily removed by etching, and also a third metal layer of a acidic or neutral copper bath.

As deposited by glow discharge first metal layer Palladium in particular is suitable since this is catalytic for the subsequent electroless metallization acts. Become other metals for the deposition of the first metal layer ver turns, the substrate is before electroless metallization in an activation solution, for example a palladium chloride solution, dipped.

Hereinafter, exemplary embodiments of the invention will be described:
As polyimide substrates, various materials are being considered. In addition to polyimide films as such, they may also be used in other laminates, pressed with other substrates, such as FR4 material (epoxy resin / glass fiber) and copper foils. Furthermore, plate-shaped polyimide substrates as well as spin-coating layers can be coated by the process according to the invention. Un polyimide is also to be understood as such material, which is generated from dissolved and / or post-cured polyimide. In addition, polyimides of different chemical structure can be used. For example, a condensation polymerization product of pyromellitic dianhydride (PMDA) with diaminodiphenyl ether (DDE) or a condensation product of 3,4,3 ', 4'-biphenyl-tetracarboxylic acid dianhydride (BPDA) with DDE or with p-phenylenediamine (PPD) can be used.

Before the deposition of the first metal layer by means of glowing If necessary, holes are made in the polyimide sub strat punched, drilled or etched. After that, that will be perfo purified substrate, for example with a Netzmit tel containing aqueous solution.

Subsequently, the surfaces to be coated by means of Glow discharge pretreated. For example, the Surfaces etched, cleaned and / or treated with reactive groups functionalized by mixing the gases with the chemical group react on the polyimide surface. The treatment Conditions for the pretreatment are, for example, in DE 37 44 062 A1. Preferably, the surfaces are in Oxygen or in an oxygen / argon or oxygen / Etched nitrogen mixture.  

The first metal layer, which is also catalytically active and haf is acting mediating, is on the pretreated so Surfaces by decomposing volatile metal compounds applied. This creates, depending on the coating conditions, a thin metal layer with a layer thickness from 0.01 μm to 1 μm.

In particular, for forming the first metal layer Volatile palladium, copper, gold or platinum compounds or decompose their mixtures in the glow discharge.

Palladium has been found to be particularly advantageous. This results for the subsequent electroless Metallabab catalytically acting metal layers, so that a further activation of these metal layers, for example with precious metal-containing solutions, usually not required is.

As volatile metal compounds come into the pressure DE 35 10 982 A1, DE 37 44 062 A1, DE 38 06 587 A1, DE 37 16 235 A1 and DE 38 28 211 C2 Verbindun described conditions, for example, copper hexafluoroacetylacetonate, dimethyl n-cyclopentadienyl-platinum, dimethyl-gold-acetylacetonate, 2- Perfluorobutene-2-silver, 2-perfluoropropene-1-silver, penta fluorophenyl-silver and in particular π-allyl-π-cyclopentadie nyl-palladium (II) used. The Ab specified there The conditions of divorce are based on the generation of the metal layers according to the inventive method accordingly transferable.

For the metallization become normal Parallelplattenreakto ren used, designed as tunnel or tubular reactors  are. The glow discharge can work with both DC and DC with alternating current (high frequency in the kHz or MHz range) he be witnesses. The pressure in the treatment chamber is in the Generally 0.1-50 hPa. Most will be near room temperature temperature at the laminate by varying the adjusted electric power of the glow discharge.

On this base metal layer, the second metal layer, for example, a palladium, a nickel / boron or Nickel / phosphorus alloy layer, by electroless metal applied from an acidic or neutral bath who the. For metal construction exclusively by electroless Metalli tion (additive) is preferably deposited palladium.

Palladium is used to create the conductor tracks after another ren procedure as the additive technique, such as example, the semi-additive method, as a second metal layer Care must be taken that this palladium layer is deposited only in a small layer thickness. This is necessary because palladium is difficult to etch and therefore only be easily removed from the surfaces can when the etchant penetrate the layer through pores and the palladium layer can lift off from below.

For the method according to the invention are the following electroless plating baths preferably used:

• 1. Nickel bath with hypophosphite as a reducing agent for the generation of nickel / phosphorus layers: Nickel sulphate (NiSO₄ · 5 H₂O) | 25-30 g / l sodium 30 g / l citric acid 2 g / l acetic acid 5 g / l aminoacetic 10 g / l Lead as lead acetate 2 mg / l PH value 6.2 temperature 80-84 ° C

The nickel / phosphorus layer contains about 4% by weight of phosphorus.

Instead of nickel salts and cobalt salts to Ab separation of cobalt / phosphor layers or a mixture of Nickel with cobalt salts for the deposition of nickel / co Baltic / phosphor layers are used.

• 2. Nickel baths with dimethylaminoborane as reducing agent for the production of nickel / boron layers: 2a. Nickel sulfate (NiSO₄ · 5 H₂O) | 25 g / l dimethylaminoboran 4 g / l sodium succinate 25 g / l sodium sulphate 15 g / l PH value 5.0 temperature 60 ° C 2 B. Nickel sulfate (NiSO₄ · 5 H₂O) | 40 g / l dimethylaminoboran 1-6 g / l sodium citrate 20 g / l Lactic acid (85% by weight) 10 g / l PH value 7.0 temperature 40 ° C 2c. Nickel sulphate (NiSO₄ · 5 H₂O) | 50 g / l dimethylaminoboran 2.5 g / l sodium citrate 25 g / l Lactic acid (85% by weight) 25 g / l thiodiglycolic 1.5 mg / l PH value 6-7 temperature 40 ° C

It can also be baths with nickel chloride or nickel acetate be used by nickel sulfate. As Reduktionsmit tel is also diethylaminoborane instead of dimethyaminoborane suitable.

• 3. Palladium baths with formic acid or derivatives thereof as reducing agent: 3a. palladium acetate 0.05 mol / l ethylenediamine 0.1 mol / l sodium 0.2 mol / l Succinic acid 0.15 mol / l pH value (adjustment with formic acid) 5.5 temperature 67 ° C 3b. palladium 0.5 mol / l 2-diethylaminoethylamine 0.6 mol / l Methansäureethylester 0.3 mol / l potassium 0.2 mol / l pH value (adjustment with formic acid) 6.0 temperature 70 ° C 3c. palladium acetate 0.05 mol / l 1,2-bis (3-aminopropylamino) ethane 0.1 mol / l sodium 0.3 mol / l Succinic acid 0.1 mol / l pH value (adjustment with formic acid) 5.9 temperature 59 ° C
• 4. Copper bath with hypophosphite as reducing agent: 4a. Copper chloride (CuCl₂ · 2 H₂O) 0.06 mol / l N- (hydroxyethyl) ethylenediamine triacetate trisodium salt 0.074 mol / l Sodium dihydrogen hypophosphite (NaH₂PO₂ · H₂O) 0.34 mol / l PH value 6 temperature 65 ° C 4b. Copper sulfate (CuSO₄ · 5 H₂O) 0.04 mol / l N- (hydroxyethyl) ethylenediamine triacetate trisodium salt 0.05 mol / l Sodium dihydrogen hypophosphite (NaH₂PO₂ · H₂O) 0.34 mol / l PH value 3 temperature 68 ° C

In addition to the baths mentioned can also other types of bath or Baths used for the deposition of other metals, though these are acidic or neutral, d. H. a pH below of about 8, preferably between 2 and 6.

On the second metal layer can further metal layers from baths for electroless or electrolytic Metallisie be put down. If the second metal layer already has a sufficient layer thickness, so that they  is pore-free, the deposited thereon Metallschich th also with alkaline Metallisierungsbädern who produced the. For this purpose, in principle all separable metals in question. There are the usual bathrooms for powerless and electrolytic metallization used.

To produce the Leiterzuge different Verfah alternatives are used:

A. "Lift-off" procedure (Substrate polyimide film, KAPTON E®)

• 1. Coating a perforated KAPTON film with liquid photoresist, expose, develop in 1% Na₂CO₃ solution
• 2. Pretreatment by means of glow discharge:
  Gas: oxygen
  Pressure: 0.25 hPa,
  Gas flow: 100 standard cc / min,
  High frequency power: 1000 W,
  Treatment time: 90 seconds,
• 3. pd deposition by means of glow discharge:
  Organometallic compound: π-allyl-π-cyclopenta-dienyl-palladium (II),
  Gas: Ar / O₂ or N₂ / O₂, each in a mixture 3: 1,
  Pressure: 0.1 hPa,
  Gas flow: 25 standard cc / min,
  Evaporator temperature: 45 ° C,
  Treatment time: 10-15 minutes,
• 4. Optionally deposit electroless palladium in a bath of formic acid as reducing agent:
  Temperature: 70 ° C,
  pH value: 6.0
  Treatment time: 5-8 minutes,
• 5. Remove photomask in acetone,
• 6. Track construction with electroless Palladiumabschei tion as step 4. to the desired Layer thickness.

The advantage of this procedure is that to the Positions where no conductor tracks are formed, only applied the metal used to produce the shadow mask and later removed. It will be at these places however, no metal used for the conductor train generation layer by decomposition of the volatile metal compounds in the glow discharge deposited. Therefore, these can be Do not place any metal contamination on the laminate surface form, so that the insulation resistance between the Lei is particularly high.

The basic metal layers on the photomask areas who chosen so thin, for example, about 0.1 microns that their Removal together with the underlying photomasks easy to succeed, d. H. without individual points of the polymer films remain on the laminate surfaces. For removal tion of the polymer films ver usual chemical solutions applies.  

B. Full-additive technique

• 1. pretreatment of a perforated UPILEX S® film (condensation product of 3,4,3 ', 4'-biphenyltetracarboxylic dianhydride with p-phenylenediamine) in the glow discharge:
  Gas: oxygen
  Pressure: 0.25 hPa,
  Gas flow: 100 standard cc / min,
  High frequency power: 1000 W,
  Treatment time: 90 seconds,
• 2. pd deposition in the glow discharge:
  Organometallic compound: π-allyl-π-cyclopenta-dienyl-palladium (II),
  Gas: Ar / O₂ or N₂ / O₂, each in a mixture 3: 1,
  Pressure: 0.1 hPa,
  Gas flow: 25 standard cc / min,
  Evaporator temperature: 45 ° C,
  Treatment time: 10-15 minutes,
• 3. Coating the film with dry film resist, be clear, develop in 1% Na₂CO₃ solution,
• 4. In the resist channel, fullyadditive electrolessly deposit palladium in a bath with formic acid as reducing agent:
  Temperature: 70 ° C,
  pH value: 6.0
  Treatment time depending on the desired layer thickness,
• 5. remove dry film resist in acetone,
• 6. Palladium differential sets with dilute HNO₃ / HCl Solution.

If the base metal layer already has sufficient conduct has ability, the second metal layer in the Re Sistkanälen be applied by electrolytic means.

C. subtractive technique / panel plating, substrate polyimide film, KAPTON H® (condensation product of pyromellitic dian hydride with diaminodiphenyl ether)

• 1. Pre-treatment of the perforated foil by means of glow discharge:
  Gas: oxygen
  Pressure: 0.25 hPa,
  Gas flow: 100 standard cc / min,
  High frequency power: 1000 W,
  Treatment time: 90 seconds,
• 2. Pd deposition by means of glow discharge:
  Organometallic compound: π-allyl-π-cyclopenta-dienyl-palladium (II),
  Gas: Ar / O₂ or N₂ / O₂, each in a mixture 3: 1,
  Pressure: 0.1 hPa,
  Gas flow: 25 standard cc / min,
  Evaporator temperature: 45 ° C,
  Treatment time: 10-15 minutes,
• 3. Depositing nickel / boron from a weakly acidic nickel / boron bath without electrolysis using dimethylaminoborane as reducing agent:
  Temperature: 40 ° C,
  Treatment time: 2 minutes,
• 4. Separate copper electrolytically in a sulphurous copper bath:
  Cupracid BL®,
  Current density: 2 A / dm²,
• 5. Coating the film with dry film resist, be clear, develop in 1% Na₂CO₃ solution,
• 6. Etching the copper and the nickel / boron layer:
  Etching solution: CuCl₂ / HCl with 120 g / l Cu ges., 3% HCl, diluted with water 1: 1,
• 7. Etching the palladium layer:
  Etching solution: HNO₃, conc./HCl, conc. in a 3: 1 mixture, diluted 1: 1 with water,
  Temperature: room temperature,
  Treatment time: 15 seconds,
• 8. Remove dry film resist in acetone.

D. Semi-additive technique / pattern plating with nickel / boron layer as the second metal layer

• 1. Pretreatment of a perforated polyimide plate by means of glow discharge:
  Gas: oxygen
  Pressure: 0.25 hPa,
  Gas flow: 100 standard cc / min,
  High frequency power: 1000 W,
  Treatment time: 90 seconds,
• 2. Pd deposition by means of glow discharge:
  Organometallic compound: π-allyl-π-cyclopenta-dienyl-palladium (II),
  Gas: Ar / O₂ or N₂ / O₂, each in a mixture 3: 1,
  Pressure: 0.1 hPa,
  Gas flow: 25 standard cc / min,
  Evaporator temperature: 45 ° C,
  Treatment time: 10-15 minutes,
• 3. Deposit electroless nickel / boron from a nickel / boron bath with dimethylaminoborane as reducing agent:
  Temperature: 40 ° C,
  Treatment time: 2 minutes,
• 4. Coating the film with dry film resist, be clear, develop in 1% Na₂CO₃ solution,
• 5. Track construction by means of electrolytic copper deposition,
• 6. deposit metal resist layer (for example Tin),
• 7. Etching the copper or nickel / boron layer:
  Etching solution: CuCl₂ / HCl with 120 g / l Cu ges., 3% HCl, diluted with water 1: 1,
• 8. Etching the palladium layer:
  Etching solution: HNO₃, conc./HCl, conc. in a 3: 1 mixture, diluted 1: 1 with water,
  Temperature: room temperature,
  Treatment time: 15 seconds,
• 9. Remove dry film resist in acetone.

In the above examples, without exception adherent Obtained metal layers, which also after a thermal Treatment, for example a soldering process, or after or during treatment with aqueous-alkaline solutions, such as For example, a developer or strip solution for a  Photoresist film, its adhesion to the polyimide surface maintained.

The adhesion of the obtained metal layers on the In particular, substrate is treated by heat treatments after Increased deposition of thicker metal layers.

If, however, for example, in the above example 4 (Semi-additive technique / pattern plating) an alkaline copper Bad used to form the second metal layer, so who although after the deposition and a tempering treatment at 150 ° C adherent copper layers on the polyimide film receive. However, the adhesive strength drops to very small Values (for example from 1.2 N / mm to 0.4 N / mm in the peel test experiment) when the polyimide provided with copper structures film is dipped in a developer solution.

Formed as films, according to the inventive method produced polyimide films with conductor tracks can in appro Neten process into stacks are glued together. A Double-sided or four-layer circuit can also be applied to one rigid carrier, for example a ceramic or FR4 plate (For example, circuit board) or a silicon substrate to be glued. You can also do two, four or more after that according to the invention produced multilayer circuits using an uncoated polyimide liner stick together and give the obtained intermediate If necessary, drill mechanically and wet in a conventional manner through-contact. The ladder trains in each Lei are then given in a conventional way to the Boh ren of holes through the stack by electroless Metallizing the hole walls electrically connected to each other.

Claims (4)

1. substrate with polyimide surfaces coated with aqueous alka Lische solutions resistant adhesive metal layers, wherein a first Metal layer in direct contact with the polyimide surfaces Decomposition of volatile metal compounds by means of glow discharge and a second metal layer on the first metal layer of a Nickel / boron alloy layer or a nickel / phosphorus alloy layer with about 4 wt .-% phosphorus or a palladium layer by electroless deposition of one from an acid or neutral set metallization are formed. 2. Substrate according to claim 1, characterized in that the pH of the metallization bath for electroless deposition between 2 and 6 is. 3. Substrate according to one of the preceding claims, characterized by a thin palladium layer as a second metal layer and on a copper layer, deposited from an acid or new tralen electroless copper bath, as a third metal layer. 4. Substrate according to one of the preceding claims, characterized by a palladium layer as the first metal layer.