DE19652991A1 - Selective gold plating of base layer-coated substrate to allow gold and aluminium wire bonding to same substrate - Google Patents

Abstract

A process for gold coating of a substrate (1) bearing a base layer (2), in order to form gold-coated first contact areas (2a-c) and gold-free second contact areas (3a-c), involves temporarily covering the second contact areas and then placing the substrate in an exchange gold plating bath. The novelty is that the gold bath has an electrolyte which causes no gold deposition on the base layer (2). Preferably, the base layer is a chemical nickel layer (2) and the gold bath is a reductive gold plating bath, the electrolyte of which preferably contains 0.1-20 g/l potassium, sodium or ammonium gold(I) cyanide or gold(III) cyanide, 0.1-25 g/l free potassium, sodium or ammonium cyanide, 0.1-50 g/l potassium, sodium or ammonium sulphite, 0.01-10 g/l aromatic nitro compound, 1-100 g/l free alkali, 1-50 g/l complex former(s) selected from hydroxycarboxylic acids, phosphonic acids, nitriloacetic acids and ethylenediamineacetic acids and 0.1-50 g/l borane and/or boranate reducing agent.

Description

The invention relates to a method for at least partial gold plating a carrier with a base layer, in which the first contact surfaces on the carrier ger, which have a gold layer, and second contact areas that are free of the are coated gold layer of the first contact surfaces are produced, wherein the second contact areas are first covered with a covering agent, where when the carrier is placed in an exchange gold bath, causing it to Most contact surfaces a pre-gilding is formed, and wherein after the Removal of the carrier from the exchange gold bath, the second contact surface Chen covering covering agents are removed.  

A very popular contacting method in electronics is the so-called "Bonding". Here electrical connections are made with gold or aluminum wires for an electronic component implemented on the carrier fen, usually gold wires with a thickness of about 30 microns or aluminum wires with a thickness of approx. 30 µ (thin wire bonding) or 300 µ (thick wire bonding) be used.

For this it is necessary that contact surfaces which can be bonded are arranged on the carrier be net. While it is possible to bond aluminum wires, this one to be attached directly to the chemical nickel layer of the support if not reinforced with a gold layer with a maximum thickness of 0.1 µ, sol Chen layers are not bonded with gold wire, as this requires an approx. 0.3 µ thick gold layer is required. This compared to the Aluminum wire bonding uses layers of significantly thicker gold layer only after one Pre-gold plating of the chemical nickel layer, which has a thickness of approx. 0.03 to 0.08 µ, are produced, this pre-gold plating in a thaw Schelectrolytes with a pH below 7.0 and at approx. 80 ° C directly on the Che mixed nickel layer is deposited. The reinforcement of this pre-gilding to about 0.3 µ then takes place in a reductive electrolyte, whereby here provided at a temperature of 80 ° C and a strongly alkaline environment becomes.

For these reasons, it is therefore not yet possible for one and the same Carrier to use gold bond wires and aluminum bond wires simultaneously.

It is therefore an object of the invention to provide a method which he possible that on the same carrier both with gold wires and with Aluminum wires can be bonded.

This object is achieved by a method in which the invention can be seen that the carrier is placed in a gold bath, the one  Has electrolytes in which no gold is deposited on the base layer of the support divorce takes place.

The measures according to the invention are advantageous created a procedure that allows you to easily access one Carrier contact surfaces for both gold wires and aluminum wires to provide. This is essentially due to the use of the invention achieved reductive gold bath according to the invention, which has the advantageous property shaft has that on the base layer, in particular a chemical nickel layer, no gold deposition takes place, so these layers for the receipt that are available with aluminum wire.

Advantageous developments of the invention are the subject of Subclaims.

Further details and advantages of the invention are the embodiment remove that is described below with reference to the single figure. It shows:

Fig. 1 is a plan view of an embodiment of a coated with a Che mixed nickel layer carrier.

Shown in Fig. 1 and indicated at 1 carrier has on its Oberflä che 1 ', a base layer, in particular a chemical nickel layer 2, the contact surfaces 2 a- 2 c are to be applied which serve for bonding of gold wires and, therefore, must have a gold layer with a layer thickness of approximately 0.3 μ gold. The carrier 1 comprises further contact surfaces 3 3 a-c ', which serve for bonding of aluminum wires and is therefore not of the contact surfaces 2 a- 2 c forming gold layer may be covered. The person skilled in the art can see that the arrangement of the contact surfaces 2 a- 2 c, 3 a- 3 c on the carrier 1 only serves to explain the method described below and in no way excludes its applicability to other contact arrangements.

In order now to ensure that the contact surfaces 3 a - 3 c intended for aluminum wire bonding are not covered in the subsequent layers of the described method by the gold layer to be produced in its method specifications, which forms the contact surfaces 2 a - 2 c, these are covered for the aluminum wire bonding certain contact areas 3 a - 3 c covered with tape or paint or a similar covering. For covering the contact surfaces 3 a- c 3 may be a variety of known per se to be used for adhesive tapes or lacquers, as they readily enclosed in the beschrie hereinafter exchange gold bath occurring thermal and / or chemical Bela stungen have grown.

The carrier 1 treated in this way is then gold-plated in an exchange gold bath in which there is a pH of preferably below 7.0 and a temperature of approximately 85 ° C., so that egg ne in a manner known per se Pre-gold plating of the contact areas 2 a- 2 c is generated with a layer thickness of 0.03 to 0.1 μ.

After rinsing and drying the carrier 1 , the covers formed by the adhesive tape, the lacquer or the other covering means are removed from the contact surfaces 3 a - 3 c in a known manner. The contact surfaces 3 a - 3 c covered in the exchange gold bath have thus retained their original chemical nickel surface.

In order to now, the contact surfaces 2 a- 2 c form for the gold wire bonding, the carrier 1 in a reductive gold bath is introduced, which applies an electrolyte ver, in which on the base layer of the carrier 1, in the case described here, the chemical nickel Layer 2 , no gold deposition takes place. It is preferred that the electrolyte is composed as follows:
The first component of the electrolyte is potassium, sodium or ammonium gold-I-cyanide or the corresponding gold-III-cyanide compounds in an order of magnitude of 0.1 g / l to approximately 20 g / l gold, preference being given to that the gold content of the aforementioned compounds is in the range of about 0.5 g / l to about 5 g / l.

A second component of the electrolyte described is free potassium, natri um or ammonium cyanide on the order of about 0.1 g / l to 25 g / l, it being preferred that the proportion of the aforementioned free cyanides in the Be ranges from about 3 g / l to 6 g / l.

Furthermore, the electrolyte has potassium, sodium or ammonium sulfite in one Of the order of about 0.1 g / l to 50 g / l, with it being preferred that the The content of the aforementioned sulfite is in the range of approximately 5 g / l to 15 g / l.

Furthermore, the electrolyte has an aromatic (mono-, di- or tri-) nitrover bond, for example 3,5-dinitrobenzoic acid, on the order of unge from 0.01 g / l to about 10 g / l, again it is preferred that the Concentration of the aforementioned acid in the range of approximately 0.05 to 1.0 g / l.

Another component of the electrolyte described is free alkali, the is preferably present as potassium or sodium hydroxide. The concentration of the free alkali is of the order of about 1 g / l to 100 g / l, the Range of about 10 g / l to 25 g / l is preferred.

Another component of the electrolyte are one or more complexing agents from the group of hydroxycarboxylic acids, phosphonic acids, nitriloacetic acids  or ethylenediamine acetic acids on the order of about 1 g / L to 50 g / l with an optimum of 10 g / l to 30 g / l.

Furthermore, the electrolyte described has one or more reduction medium from the group of boranes or boranates, the proportion of these Re reducing agent in the order of about 0.1 g / l to 50 g / l with a Optimal from approx. 1 g / l to 10 g / l.

To accelerate the reaction of the electrolyte, a Re action accelerator, preferably a water-soluble thallium I compound be provided in the order of 0.1 mg / l to about 100 mg / l is added to the electrolyte, the preferred range of the aforementioned Compound ranges from about 1 mg / l to 20 mg / l.

Experiments have shown that a preferred composition of the electrolyte is essentially as follows:

• 1.0 g / l gold as free potassium gold I-cyanide,
• - 5.0 g / l free potassium cyanide,
• 50 g / l of 1-hydroxide-ethane-1,1-diphosphonic acid,
• - 10 g / l potassium sulfite
• - 0.2 g / l 3,5-dinitrobenzoic acid,
• - 22 g / l free potassium hydroxide
• - 5.0 g / l dimethylamine borane,
  preferably 5.0 mg / l thallium is added as thallium I-sulfate.

A temperature of un dangerous 60 ° to 95 ° of the electrolyte and in particular the range from 75 ° to 85 ° C preferred.  

The carrier 1 is left in a gold bath at a temperature of preferably 80 ° C. until a layer thickness of approximately 0.3 μ gold has been deposited on the contact surfaces 2 a- 2 c.

Since the electrolyte described above has the advantageous characteristic that occurs in the reductive gold solution on the electroless nickel layer 2, and thus also on the contact layers 3 a- 3 c no gold deposition, destined for the Alumi nium bands contact surfaces 3 are a - 3 c does not cover the gold layer and is therefore unchanged even according to this procedure.

The carrier 1 thus has contact layers 2 a- 2 c, which have a thickness suitable for the gold wire bonding layer of gold, and contact surfaces 3 a- 3 c which are unvergoldet on so that on the carrier 1 in both aluminum - as gold wires can also be bonded.

Should c, the remaining areas of the base layer 2, so in the descriptions here NEN case, the contact surfaces 3 a-3, coated with a thin layer of gold who to, this is achieved in that the above treated support 1 after the reductive gold bath in the exchange gold bath described above is introduced until the free surfaces are coated with a thin gold layer, which is still bondable with aluminum bath. It is preferred that the thickness thereof be approximately between 0.01 µ to 0.09 µ.

Claims (16)

1. A process for at least partial gold coating of a carrier (1) having a base layer (2), wherein the first contact surfaces (2 a- 2 c) on the support (1), having a gold layer, and second contact surfaces (3 a- 3 c) that are free of the coated gold layer of the contact surfaces ( 2 a- 2 c), he is produced, the second contact surfaces ( 3 a- 3 c) being covered first with a covering agent, the carrier ( 1 ) in an exchange gold bath is introduced, and as a result pre-gold plating is formed on the first contact areas ( 2 a- 2 c), the second contact areas ( 3 a- 3 c) being removed after the carrier ( 1 ) has been removed from the exchange gold bath abdec kenden cover means are removed, characterized in that the carrier is introduced into a gold bath which has an electrolyte in which there is no gold deposition on the base layer ( 2 ) of the carrier ( 1 ). 2. The method according to claim 1, characterized in that a chemical nickel layer ( 2 ) is used as the base layer of the carrier ( 1 ), and that the gold bath is a reductive gold bath. 3. The method according to claim 2, characterized in that an electrolyte is used for the reductive gold bath, the

• Potassium, sodium or ammonium gold-I-cyanide or gold-III-cyanidver compounds in the order of about 0.1 g / l to about 20 g / l,
• free potassium, sodium or ammonium cyanide in the order of about 0.1 g / l to 25 g / l,
• Potassium, sodium or ammonium sulfite in the order of about 0.1 g / l to about 50 g / l,
• an aromatic nitro compound of the order of about 0.1 g / l to about 10 g / l,
• free alkali in the order of about 1 g / l to about 100 g / l,
• one or more complexing agents from the group of the hydroxycarbon acids, phosphonic acids, nitriloacetic acid or ethylenediamine acetic acids in a range from approximately 1 g / l to approximately 50 g / l,
• - Contains one or more reducing agents from the group of boranes or borates in the order of 0.1 g / l to 50 g / l.

4. The method according to claim 3, characterized in that the electrolyte un contains about 0.5 g / l to about 5 g / l gold. 5. The method according to any one of the preceding claims, characterized net that the electrolyte from about 3.0 g / l to about 6.0 g / l of free potassium, Contains sodium or ammonium cyanide. 6. The method according to any one of the preceding claims, characterized net that the electrolyte potassium, sodium or ammonium sulfite in sizes order of about 5.0 gl to about 15.0 g / l.   7. The method according to any one of the preceding claims, characterized net that the electrolyte is the aromatic nitro compound in the order of magnitude contains from about 0.05 g / l to about 1 g / l. 8. The method according to any one of the preceding claims, characterized net that the free alkali is present as potassium or sodium hydroxide. 9. The method according to any one of the preceding claims, characterized net that the free alkali in the order of about 10 g / l to unge about 25 g / l is present. 10. The method according to any one of the preceding claims, characterized in net that the reducing agent in the order of about 1 g / l to about 10 g / l. 11. The method according to any one of the preceding claims, characterized in net that a reaction accelerator is added to the electrolyte. 12. The method according to any one of the preceding claims, characterized in net that the reaction accelerator is a water-soluble thallium I verbin dung is. 13. The method according to any one of the preceding claims, characterized in net that the concentration of the water-soluble thallium I compound in egg on the order of about 0.1 mg / l to about 100 mg / l and above is preferably in the range of approximately 1 mg / l to 20 mg / l.   14. The method according to any one of the preceding claims, characterized net that the aromatic nitro compound is a mono-, di- or tri-nitroverbin dung is. 15. The method according to any one of the preceding claims, characterized in net that the nitro compound dinitrobenic acid, especially 3.5 dinitrobene zoic acid, is. 16. The method according to claim 1, characterized in that the carrier (1) is in turn introduced to the treatment in the reductive gold solution into the exchange gold bath to the second contact surfaces (a- 3 3 c) apply a thin layer of gold.