coating cavity on the hole wall of circuit board
Discussion on the causes and countermeasures of coating cavity on the hole wall of circuit board
Chemical copper deposition is a very important step in the metallization of printed circuit board holes, the purpose of which is to form extremely thin conductive copper layer on the hole wall and on the copper surface. The hole in the hole coating is one of the common defects in the metallization of the printed circuit board hole, and it is one of the items that easily lead to the mass scrapping of the printed circuit board. Therefore, solving the hole problem of PCB coating is an important part of PCB manufacturers' control. However, because of the variety of reasons causing the defects, only by accurately judging the characteristics of the defects can the solutions be found effectively.
1, the hole wall coating cavity caused by PTH
The voids caused by PTH are mainly punctate or annular cavities, and the reasons are as follows:
(1)Copper content in sunk copper cylinder, concentration of sodium hydroxide and formaldehyde
The solution concentration of the copper cylinder is the first consideration. Generally speaking, the copper content, the concentration of sodium hydroxide and formaldehyde is proportional to each other, and when any one of them is below the standard value of 10 percent, it will destroy the balance of the chemical reaction. Lead to poor deposition of chemical copper, point-shaped cavity. Therefore, priority to adjust the copper tank of the various parameters of the solution.
(2)Temperature of Liquid in the tank
The temperature of the bath solution also has an important effect on the activity of the solution. There is a general requirement of temperature in each solution, some of which should be strictly controlled. Therefore, the temperature of the bath solution should be paid close attention to at any time.
(3)Control of activation solution
The low divalent tin ion will lead to the decomposition of colloidal palladium and affect the adsorption of palladium, but it will not cause a big problem as long as the activation liquid is added at a fixed time, and the emphasis of the activation liquid control is that it cannot be stirred by air. Oxygen in the air oxidizes tin divalent ions, and no water enters, which results in the hydrolysis of SnCl2.
(4)The temperature of cleaning
The temperature of cleaning is often ignored, the best temperature of cleaning is above 20 ℃, if it is below 15 ℃, it will affect the effect of cleaning. In winter, the temperature of water will become very low, especially in the north. The temperature of the plate will also become very low after cleaning. After entering the copper cylinder, the temperature of the board will not rise immediately, and the effect of deposition will be affected by missing the golden time of copper deposition. Therefore, where the ambient temperature is relatively low, Also pay attention to the temperature of the washing water.
(5)Use temperature, concentration and time of the whole pore solution
The temperature of the solution has strict requirements, too high temperature will cause the decomposition of the whole pore agent, make the concentration of the whole pore agent lower, and affect the effect of the whole pore. The obvious feature is that there is a punctate hole in the glass fiber cloth in the hole. Only when the temperature, concentration and time of the solution are properly matched, can the effect of the whole pore be obtained. At the same time, it can save cost. The concentration of copper ion accumulated in the solution must be strictly controlled.
(6)Temperature, concentration and time of use of reductant
The effect of reduction is to remove the residual potassium manganate and potassium permanganate after drilling.Losing control of the relevant parameters of the solution will affect its action, and the obvious characteristic is that the voids appear in the resin in the pore.
(7)The oscillators and the runaway swing
The oscillators and the runaway swing can cause annular holes, mainly because the bubbles in the holes can not be eliminated, especially the small hole plates with high thickness to diameter ratio. The obvious feature is the symmetry of the holes and the normal thickness of the copper parts in the holes. Graphic plating layer (secondary copper) wrapped all-board coating (primary copper).