Alkaline Formulant
An aqueous chemical solution composed of dissolved ammonia gas and copper compounds is widely utilized in the printed circuit board industry for selective copper removal. This fluid, acting as ammonium hydroxide etchant, dissolves exposed copper cladding while leaving metallic resists unaffected.
Etching Mechanism
Operating parameters dictate the rate of the chemical reaction and the anisotropy of the metal removal. A stable solution requires a continuous replenishment system to balance the concentration of copper ions, maintain the pH between eight and nine, and sustain the specific gravity. If the pH drops below the threshold, copper salts precipitate on the boards, which halts the production line.
Process Constraint
Control of the lateral etch factor remains the primary metric for trace geometry preservation in fine-line circuit board manufacture. When the chemical reacts with the copper, it also progresses horizontally under the resist boundary, which causes undercut. Process engineers track the etching factor by dividing the vertical etch depth by the lateral undercut dimension.
Higher etch factors correspond to more vertical sidewalls, which ensures that impedance remains within designed tolerances across the entire circuit trace profile. Regular titration of chloride ions and active ventilation of ammonia gas prevent crystallization on the equipment.
