PCB hole wall plating cavity phenomenon and countermeasures
Chemical precipitation of copper is PCB circuit board hole metallization process, a very important process, its purpose is in the hole wall as well as the copper surface, constituting a very thin layer of conductive copper, for the latter side of the plating to prepare. The hole wall plating is one of the common shortcomings of PCB hole metallization, but also easy to cause bulk scrap of printed circuit boards one of the project, so the solution to the problem of printed circuit board plating is a printed circuit board manufacturers focus on manipulation of a content, but due to the formation of its shortcomings for a variety of reasons, as long as the precise judgment of its shortcomings of the characteristics of the usefulness of finding a solution to the problem of the plan.
A. PTH Formed By The Hole Wall Plating Flooding
PTH formed by the hole wall plating flooding is mainly point-like or ring-shaped flooding, the specific causes are as follows:
a, The copper content of the immersion copper cylinder, sodium hydroxide and formaldehyde concenttion
The solution concentration of the copper cylinder is the first thing to consider. Generally speaking, the copper content, sodium hydroxide and formaldehyde concentration is proportional, when the content of any one of them is less than 10% of the normative value will damage the balance of the chemical reaction, the formation of chemical copper buildup is poor, presenting a point-like blanking. So give priority to adjusting the parameters of each potion in the copper tank.
b, The Temperature of The Tank Solution
The temperature of the tank solution also has an important influence on the activity of the solution. There are generally temperature requirements in each solution, some of which are to be strictly manipulated. Therefore, the temperature of the bath solution should be emphasized at all times.
c, Activation Solution Control
Divalent tin ions low will form colloidal palladium differentiation, affecting the adsorption of palladium, but as long as the activation solution punctually add supplement, will not form a major problem. The key point of activation liquid control is not to mix with air, the oxygen in the air will oxidize the divalent tin ions, and at the same time there can not be water into the formation of SnCl2 hydrolysis.
d, Cleaning Temperature
Cleaning temperature is often ignored, cleaning most good temperature is above 20 ℃, if below 15 ℃ will affect the cleaning effect. In the winter time, the water temperature will become very low, especially in the north. Due to the low temperature of water washing, the temperature of the plate after cleaning will also become very low, the temperature of the plate after entering the copper tank can not immediately rise, will be because of the missed copper stacking of the golden time and affect the role of the stacking. So in the low ambient temperature of the local, also pay attention to the temperature of the cleaning water.
e, The Application Temperature, Concentration and Time of The Whole Hole Agent
The temperature of the liquid has strict requirements, too high a temperature will form the differentiation of the whole pore agent, so that the concentration of the whole pore agent becomes low, affecting the role of the whole hole, which is a significant feature of the glass fiber cloth in the hole in the point of empty flooding. As long as the temperature of the liquid, concentration and time of proper cooperation, to get a good role of the whole hole, but also to save money. The concentration of copper ions accumulated in the liquid, it is also necessary to strictly control.
f, Temperature, Concentration and Time of The Recovery Agent
The role of recovery is to remove the residual potassium manganate and potassium permanganate after drilling and contamination, the liquid parameters related to the loss of control will affect the role of its significant feature is the resin in the hole at the point of empty flooding.
g, Vibrator and Shaking
Vibrators and shaking out of control will form a ring-shaped void, which is mainly due to the failure to eliminate the air bubbles in the hole, with a high thickness-to-diameter ratio of the small hole plate most of the significant. Its distinctive feature is the hole in the void symmetry, and the hole in the copper part of the copper thickness is normal, graphic plating layer (secondary copper) wrapped in a full-plate plating layer (primary copper).
B. Patterned Handling Formed By The Hole Wall Plating Flooding
Graphic handling of the formation of the hole wall plating layer is mainly formed by the hole mouth ring and the hole in the ring of blanking, the specific reasons for the occurrence of the following:
a, Pre-treatment Brush Plate
The pressure of the brush plate is too high, the copper layer at the full-plate copper and PTH holes is brushed off, so that the graphic plating can not be plated on the back of the copper, which occurs in the aperture ring-shaped blanking. The distinctive feature is that the copper layer at the aperture is gradually thinning and the graphic plating wraps around the full-plate plating. So by doing the abrasion test, manipulate the pressure of the brush plate.
b, Orifice Residual Glue
In the graphics handling process is very important to the control of process parameters, because of poor pre-treatment drying, film temperature, pressure is not appropriate will form the marginal parts of the aperture presents residual glue and lead to the aperture of the ring of the empty flood. Its distinctive features are normal thickness of the copper layer in the hole, single-sided or double-sided aperture presents a ring-shaped void, has been extended to the pad, the edge of the fault there are significant traces of etching, graphic plating layer does not wrap the whole board.
c, Pretreatment Micro-etching
Pre-treatment micro-etching should be strictly manipulated, especially to manipulate the number of rework of the dry film plate. Mainly in the middle of the hole due to plating uniformity problems plating thickness is thin, rework too much will shape to meet the plate holes in the copper layer thinning, and most of the end of the hole occurred in the middle of the ring without copper. Its distinctive feature is the hole in the whole plate plating layer gradually thinning, graphic plating layer wrapped around the whole plate plating.
C. Graphic Plating Formation of Hole Wall Plating Flooding
a, Graphic Plating Microcorrosion
The amount of micro-etching graphic plating should also be strictly manipulated, the shortcomings of its occurrence and dry film pretreatment micro-etching is basically the same. Severe when the hole wall will be a large area without copper, the thickness of the full plate layer on the surface of the plate is significantly thinner. So to keep measuring the micro-etching rate, most good by conducting DOE experiments to optimize the process parameters.
b, Tin Plating (lead tin) Poor Dispersion
Due to the poor function of the solution or the lack of shaking and other elements of the tin-plated layer thickness is lacking, in the back of the film and alkaline etching of the hole in the middle of the tin layer and copper layer etched off, occurring ring-shaped blanking. Its distinctive feature is the hole in the copper layer thickness is normal, the edge of the fault there are obvious traces of being etched, graphic plating layer does not wrap the whole plate. For this situation, you can add some tin-plated light agent within the dip acid before tin-plating, you can increase the board's wettability, while increasing the amplitude of shaking.
D. The Conclusion
Formation of the plating of many factors, most common is PTH plating flooding, by manipulating the relevant process parameters of the potion can be useful to reduce the occurrence of PTH plating flooding. But other elements should not be ignored, as long as through detailed observation, to understand the reasons for the occurrence of plated layer flooding and the characteristics of the shortcomings, in order to timely and useful solutions to the problem, to protect the quality of the product.
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