DD232073B1 - METHOD AND SOLUTION FOR ELECTROLYTIC ACTIVATION OF NICKEL - Google Patents

Description

Embodiments

The invention will be explained in more detail below with reference to two embodiments. This is done in the form that the underlying technical problem and then the mode of action of the activation and the composition of the activation solution are described using the example. In the manufacture of electronic components of various types, silver is used as the contact material. In the technological process, especially when using a eutectic chip contacting method, temperature loads of around 500 ° C. occur. When using copper or copper alloys as the carrier strip base material, problems can arise in the processing of the component or in its reliability, which are caused by copper diffusion and by the silver layer. Depending on the characteristics and mounting peculiarities, in order to suppress such effects, silver layers of bit in the chip bonding area are generally required. Using nickel interlayers can significantly reduce the silver layer. This achieves considerable precious metal savings. When using the nickel activation solution according to the invention can be obtained from cyanide / alkaline silver electrolyte well adhering Siiberschichten while preserving all technologically significant properties, which is not possible with conventional activation solutions. With the first embodiment carrier tape made of CuAg 0.1 mm is processed on a reel-to-reel system. The processing is done so that a Abkochentfernung follows a cathodic degreasing and is followed by a pickling. This is followed by partial nickel plating. This is followed by activation according to the invention. The activation process is followed by partial silvering, silvering and silver stripping. Both processes are also partially performed. The activation according to the invention takes place under the following technological conditions: Solution composition

NiCl ₂ · 6H ₂ O 200 g / l HCL (37%) 100 ml / l Cu ³⁺ (as CuCl ₂ .2H ₂ O 2 g / l 4s room temperature 4 A / dm ² intensive flooding

- Treatment time

- temperature

- cathodic current density

- Badbewegung

Upon activation, copper and nickel are deposited in layer thicknesses of a few nanometers. The layers deposited from the following shiny silver bath are uniformly glossy and highly adhesive. The adhesive strength of the layer is assessed semi-quantitatively by a modified soldering process. Values are achieved which correspond to the adhesion of silver to activated copper. The process is optimized so that copper diffusions can not be registered. In a second embodiment, the application of the activation solution according to the invention will be described with reference to the refinement of Nicosil 63 carrier tape. The Nicosil 63 carrier tape is processed on a reel-to-reel system. The decoction and the cathodic degreasing are followed by an H ₂ SO ₄ pickling. This is followed by activation, pre-silvering and silvering as well as silver stripping. The activation according to the invention takes place under the following technological conditions:

- solution composition NiCl ₂ · 6 H ₂ O 200 g / l

HCL (37%) 100 ml / l

Cu ²⁺ (as CuCl 2 -2H ₂ O) 8 g / l

- Cathodic current density 6 A / dm ²

Treatment time, temperature and bath movement are analogous to the first embodiment.

The direct silver plating of stainless steel base plates for power transistors will be described in a third embodiment. The galvanizing material is treated in a drum and pretreated by a technology analogous to the embodiment 2. The activation in the electrolyte according to the invention takes place under the following conditions: - Solution composition NiCl ₂ H ₂ O 150 g / l

HCJ (37%) 150 g / l

Cu ² (as CuCl ₂ .2 H ₂ O 0.1... 0.2 g / l

- cathodic current density 2 A / dm ² treatment time ^{15 sec}

- Temperature room temperature

- movement goods movement

Claims (2)

claims: 1. Solution for the electrolytic activation of nickel, nickel alloys or stainless steels to improve the adhesion of electroplated silver layers consisting of 150 to 300 g / l nickel chloride hexahydrate and 80 to 180 g / l hydrochloric acid (37%), characterized in that they additionally 0.1 to 10 g / l of Cu ²⁺ as a soluble copper salt. 2. Solution for electrolytic activation of nickel, nickel alloys and stainless steels according to item 1, characterized in that copper chloride is used as the copper salt. Field of application of the invention The application of the invention is possible as a pretreatment solution in electroplating plants of all branches of industry for the galvanic silvering on nickel, nickel alloys or stainless steels. It is particularly suitable for high-speed processes with short dwell times in the activation electrolyte. Characteristic of the known technical solutions Galvanic silver plating processes of nickel, nickel alloys or stainless steels are always a problem due to the formation of highly stable passivation layers. The adhesion of the silver layers is always insufficient, ignoring intensive pretreatment and therefore requires special attention. Numerous pretreatment and activation processes are described in the literature to ensure sufficient adhesion of the silver shells to the abovementioned base materials. Known are electroless pickling from dilute acids and acid mixtures. In part, it is working with the addition of nobler metals that block on the one hand by electroless deposition of the base material surface and thus prevent the formation of a new passivation layer and on the other hand reduce the potential difference between base material and silver salt. Same or even more intense effects are achieved in the known methods in which the action of acid is still supported by electric current. Both anodic and cathodic processes are common. Also, the reciprocal polarity of Galvanisierungsgutes in a certain rhythm is possible and practicable. For all these known methods, sulfuric acid or hydrochloric acid is used in the simplest case. Numerous examples of the galvanic deposition of intermediate layers prior to the actual silver plating are also known. These essentially fulfill the same functions as the abovementioned electrolessly deposited intermediate layers. Examples of these are the hydrochloric acid nickel chloride solutions described in the relevant literature (Dettner / Elze "Handbuch der Galvanotechnik") according to the WOOD or WESLEY type or the hydrochloric acid copper chloride solution according to BUSS (Krusenstjern "Edelmetallgalvanotechnik"). For example, West German Offenlegungsschrift OS 2 503 317 proposes the addition of palladium chloride or silver nitrate to an acid mixture consisting of sulfuric acid, phosphoric acid and acetic acid. Particularly high demands on the adhesion of galvanic silver layers to nickel and melts are made in carriers for microelectronic devices. Due to the high thermal and mechanical stresses occurring in the assembly process, partial detachment of the silver layers from the substrate can occur. This leads to a significant reduction in the reliability of the components up to complete inoperability. These major drawbacks and difficulties try to compensate most component manufacturers by applying the silver layers directly to copper or copper alloys. The higher silver use compared to nickel-plated carriers is compensated by a higher stability of the galvanic process. Object of the invention The aim of the invention is to develop an activating solution which makes it possible to deposit silver layers on nickel, nickel alloys and stainless steels in such a way that optimal adhesion of the silver layer is ensured even under the mounting conditions for electronic components. The activation solution should be applicable to the deposition of silver layers of cyanide / alkaline electrolytes. Explanation of the essence of the invention In many processes in the art and in particular in the assembly of semiconductor devices, electroplated silver layers are exposed to high thermal and mechanical stresses. Depending on the properties of the base materials used, disruptive diffusion processes may play a role, which can only be controlled by relatively large silver layers. Here, the application of nickel layers has proven to be a diffusion barrier. From this, the technical problem to be solved is derived from developing a solution for the electrolytic activation of nickel, the use of which enables silver to be deposited on nickel in such a way that a good bond strength between nickel and silver is ensured even under the highest thermal and mechanical stresses. This good adhesive strength must also be ensured when using strongly alkaline / cyanide lustrous silver electrolytes. According to the invention, this object is achieved by using an acidic, nickel-containing activation solution according to the WOODS or WESELEY type, to which a copper (H) salt is added. The activation process takes place cathodically with deposition of nickel and copper in the nanometer range with very short treatment times.