动态化学镀铜沉积

The present paper describes a new direct chemical plating method of copper, called Dynamic Chemical Plating. This low cost technology is based on spraying separate aqueous solutions containing copper metallic ions and Borohydride reducing agent. It is able to plate chemical copper at 30 µm/h at room temperature and may be used as an industrial process for metallizing polymers and non-conductors in general. The copper plating dynamic parameters were studied as well as the substrate characteristics in order to be metallized. The wettability of the plastics surfaces and the use of a coupling agent plate, as an under-coat metallic layer, are major important parameters to start plating and increase the adhesion of metallic copper layer to the substrate. Effects of pre-treatment conditions such as corona discharge, the plating kinetics and electrical properties of the copper film are also investigated.

Introduction

Autocatalytic or electroless copper plating is widelyused to metallize non-conductor surfaces and it is a keytechnology for manufacturing printed circuits boardsIt is also used for connectors applications and as wellas to pre-plate a conductive thin film on plastics forsubsequent electrochemical plating. One of its mostsuccessful applications also is Electromagnetic Interference Shielding (EMI/RFI). This “wetplating technique is a unique approach to obtain perfectly homogeneous and uniform metal deposits on a catalytic surfaceand it can be applied to any complex or intricate shapesubstrate. In spite of all these advantages, electrolessplating is still suffering from several practical problemssuch as:

• the bath control and limited solution life 

• the toxicity (i.e.: carcinogen formaldehyde compound) and ecological disadvantages (wastes treatment, use of chromic etching, ...) 

• the diffificulty to plate large dimensions parts 

• the plating rate which is limited to 5 µm/h for most of commercial available baths.

Added to these problems, another very important industrial inconvenience concerns the high number ofprocessing steps, particularly the activation step. Soseveral processes have been developed as possible sub.stitutes. They are usually referred to as “direct plat-ing’since the non-conductive substrate can be copper electroplated directly after a specifific activation step without the need for a conductive electroless copper film.

These processes can in general be categorised intothree groups. The first alternative is based on colloidalcarbon or on a conductive polymer film to replace theelectroless copper film [1, 2]. The second group usesBridging Ligands based on a mixed Pd/Sn catalyst coupled with a sulphide solution dip [3, 4]. The third groupuses coupling agents such as silanes which fix Pd(Il) orCu(II) [5, 6] as ultra thin, not to say atomic, conductive layer.

Although these alternative processes decrease thenumber of the global plating process steps, they stillhave the problems pinpointed above. Moreover, theyare very expensive. For example, the palladium, usedto obtain a catalytic surface in view to copper or nickeldeposition, has a price that increased from 100$ peroz in 1997 up to 850$ per oz in 2000 [7]. The greatdemand of this material and the rare sources of supplyexplain the financial market of palladium is so tenseand unstable.

Stremsdoerfer et al., have developed and presenteda new “direct plating process which avoid the dis-advantages listed above and in particularly the Pd/Snstep activation [8, 9]. In few seconds, it is possibleto plate non-conductor surface with a Ni, Cu or Cofilms without a Pd catalytic activation step. For exam-ple, on polymers, a 0.3 um NiB metallic underlayer,which is enough to start electroplating deposition, is plated in 90 s at room temperature. This process namedJetMetalTM, is also called “Dynamic Chemical PlatingDCP A detailed explanation and discussion of the dynamic aspect of the process in comparison to differentconventional wet techniques called “Static ChemicalPlatingare given elsewhere [10, 11]. The novelty ofthis Dynamic Chemical Plating is based on a sequen-tially highly controlled supply of the material (metallicions Ni2+, Cu2+, Co2+, Ag+) and the energy source(reducing agent) to the substrate. In other words it canbe described as a metal plating process using intermittent spraying of two or several solutions simultane.ously. Using compressed air and a double nozzle spraying gun, the reducing and oxidising agents are sprayedat the same time but separately onto a non-conductorsurface. Thus, a very thin liquid film is formed. Thisfilm is adsorbed on the surface and contains the active species. This film is also thermodynamically unstable which means that the oxidation-reduction reactionwill occur spontaneously. But under some experimentalconditions, this spontaneous reaction can be controlledto avoid coarse precipitation.