Surface treatment before the most flame proof prin

Surface treatment before solder proof printing

I. Introduction

at present, there are many specifications for solder proof printing in the printed circuit board industry, from the previous ipc-sm-840c (version C of 1996.1 and AMENDMENT1 of 2000.6), but there are also requirements for the treatment before solder proof 285 fire damper. Many downstream customers began to re regulate the thickness of copper foil, which evolved from no regulations to more than 1.1mil now, At this time, it is necessary to be more strict with the pre welding treatment. Of course, it has a lot to do with the increasingly fine line width (from 0.3mm to less than 1mil of BGA). Please look at the following slices, and it is not difficult to understand the requirements:

figure 1,2: what is described is that after the pre welding surface treatment, one side of the line becomes thinner and the thickness is uneven, resulting in the increase of impedance, The generation of pulse square wave of board signal is extremely unfavorable and unstable. Especially in today's products in the world, high current electrical products are increasing. Therefore, some downstream customers begin to pay attention to the thickness of copper foil, and if necessary, high voltage resistance tests must be carried out

Figure 3: the problem is that bubbles are easy to produce at the corner during Anti welding. Investigate the reasons: first, the water at the corner of the line is not dried in time during surface treatment, and then the relationship between the printing speed and ink. If bubbles are generated at the corner of the side of the circuit, the anti welding layer will peel off during high-temperature welding, which is why some printed circuit boards are easy to have the anti welding layer fall off at the edge of the circuit during high-temperature wave soldering

therefore, the treatment before anti welding has a considerable impact on the circuit and anti welding printing

second, the role of circuit and anti soldering

to understand the impact of pre soldering treatment on printed circuit boards, we first start to understand the relationship between them, which can realize closed-loop control such as equal rate loading, equal rate deformation, equal rate displacement, equal rate strain, etc. there are two main parts of the circuit board:

first, circuit: We 1 will do our best. This is the part of the circuit board used to transmit signals, In different circuit boards, the materials used for circuits are different, including copper, silver, gold, nickel, carbon ink, etc. Copper is the most widely used. In the development, there are copper through holes, secondary copper, silver through holes, chemical nickel gold, carbon ink through holes, and so on

second, anti welding: mainly used to protect lines. Some articles are called green paint. Why is it emphasized here that it is called solder proof printing instead of green paint? In the market, we can see that a large part of anti welding is green, but since Sony's SS-00259 specification and Europe's WEEE and RoHS were issued worldwide in 2003, the requirements for harmful substances have been further improved, especially for PBB, PBDE and related halogen regulations, which have attracted the attention of many businesses, and environmental friendly inks have been used, followed by blue anti welding inks

in order to cover the high-density anti welding layer on the surface of the line, the surface must be roughened. After treatment, the line surface must be dried in time to prevent oxidation, which will cause the anti welding layer to fall off after drying

III. The impact of surface treatment on printing

the general process of surface treatment is: heavy brushing, light brushing, water washing, and surface drying

grind the copper foil surface with a steel brush or non-woven cloth brush. The main parameter index is the grinding range. When the width is too large, it is easy to produce copper powder and a small amount of residual inter circuit. After anti welding printing, there is a micro short circuit. If the universal hydraulic test function of the tester is general, it will be difficult to find, causing direct losses to downstream customers. In addition, it will also form the phenomenon shown in Figure 1 above; When the width is too small and the surface treatment is incomplete, that is, there are impurities on the surface of the copper foil, which affects the density of the anti welding layer, and it is easy to cause the solder resist to fall off during wave soldering

the temperature and speed of surface drying also have quite important factors, and its parameters need to be set according to the size of typesetting. Generally speaking, no water vapor remains on the surface of the substrate through visual observation. If there are water drops or water vapor left on the board, first of all, the ink cannot be closely attached to the substrate during printing, which is easy to peel off; Secondly, when water adheres to the plate or negative, it causes abnormal patterns (water marks, ink diffusion, etc.)

finally, there are many problems of pre printing treatment in the industry, but in the acceptance standard of IPC, there are few definitions of adverse phenomena, so I am willing to discuss its impact on electrical performance with you here

source: PCB City