Metal Finishing Guide Book


Issue link:

Contents of this Issue


Page 254 of 843

Figure 4: Tensile strength measured at 24°C and 35°C.. Figure 5: Elongation measured at 24°C and 35°C. or other cooling methods while still obtaining a desired plating deposit. A new direct-current process for plating smooth, bright, and planar copper layers at temperatures up to 40°C (104°F) is described in this article. The method outlined herein yields excellent microdistribution. The organic brightener used assists in reducing the surface-to-hole thickness ratio, as well as improving the ductility and tensile strength of the copper deposit. Furthermore, the thermal characteristics of the deposited copper are excellent. ACID COPPER BATH CONSTITUENTS The developed process was formulated for highvolume rigid PWB production. A sulfate-based copper plating system that is well established for PWB fabrication was utilized. The method presents low operational costs and is easy to control. The development work goal was to achieve a process that is temperature tolerant up to 40°C (104°F). The bath composition, as well as the plating parameters, are given in Table 1. HT 100 Make-up is a mixture of wetter/suppressor that aims to improve start-up and decrease dummy plating time for new baths. It is used only for new make-ups and after carbon treatments. HT 100 Brightener is responsible for copper grain refinement and internal stress reduction. It also has a leveling effect to smooth rough holes. HT 100 Wetter is a combination of organic additives that is used for replenishment during the plating process. TEST VEHICLES The test vehicle used in the process evaluation was 1.6-mm thick boards with various-sized through-holes. The through-hole diameters were 0.2, 0.25, 0.35, and 0.5 mm. The process flow included the following operations: Acid cleaner: Wets the hole and removes light soils. Rinse Micro-etch: Etch undercuts and remaining debris to ensure excellent copper-to-copper adhesion. Rinse Acid dip: Acidifies copper surface prior to plating. The plating was performed at current densities of 1.0, 1.5, 2.0, 2.5, and 3.0 ASD. The solution temperature was in the range of 22–40°F. 247

Articles in this issue

view archives of Metal Finishing Guide Book - 2013