Screen printing is a double-sided circuit board commonly used printing methods, in the flexible circuit board printing, contrast more see is single-sided printed circuit boards, two panels are relatively few, but double-sided hard circuit board is more than the comparison. Double PCB The principle of double-sided PCB and the production of printed hard circuit boards are the same, printed hard PCB is the completion of the two-layer copper line between the conduction; double-sided PCB is a conductive carbon ink or silver ink soaked by a small hole, irrigation through the upper and lower two-tier lines. Print line version of the use of conductive inks mainly silver ink and carbon ink, the following is a brief introduction to the carbon ink for conductive ink double-sided circuit board printing process and demand attention.
1. Upper line Screen printing
The first selection of data, baking pretreatment to prevent the reduction of data deformation to bring trouble after the process. The selected scale precision requires a higher line for the upper line (numbered a to facilitate differential base line B). Double PCB With carbon ink screen printed A-side line, screen printing process to pay special attention to control the thickness of ink to ensure the satisfaction of the circuit resistance requirements.
2. Punching Carbon hole
The diameter of the carbon-filled hole is generally 0. 8~1. 0 M M. Pay attention to the carbon hole must choose the right, the hole is too large, in the screen printing base line, after the carbon-filled pores saturated with too much ink, the remaining inks will flow through the carbon hole residue in the screen printing work platform, simple lead to the short circuit. And because of the limit of the width of the line, it is impossible to fill the carbon hole too much. But if the carbon hole is too small, stamping die manufacturing difficult, Double PCB and manufacturing circuit board data p e t after punching carbon hole, blanking is not easy to fall, it is necessary to rely on artificial shedding. Otherwise, I will cover the carbon hole in the process, hinder the ink activities, affect the upper and lower two-layer circuit guide. And the carbon hole is too small, through the amount of ink, Double PCB lack to make the upper and lower two-layer circuit guide. In the process of stamping the carbon hole, the need to pay special attention to is a face (upper line surface) is necessary to face up, so the intention is to make the stamping front (that is, the flying edge, sawtooth-like protuberance) toward the side of the screen, its effect will be fully reflected in a process. In order to add the conduction probability of the two-layer line, a carbon-filled hole can be added at the same place, Double PCB and the distance between the two holes should not be too wide. In view of the small size of the carbon-filled hole, the interval is closer, stamping die manufacturing more difficult, the general manufacture of two sets of molds, one punch two holes in a single, that is, half of the carbon-filled hole two times completed.
3. Basic line of the screen printing
To locate the hole as the benchmark, in the screen printing base line. Because the front facing B, after the screen printing is also covered with a layer of ink, in the gravity effect, the active carbon ink more smoothly fill through the carbon hole, and a surface line (upper line) connected, so that a, b on both sides of the line. If the front is facing a, in the B-face screen printing, ink through the pouring carbon hole to the A-side line, by the blocking of the front, the Beatles have a certain height H, ink is not easy to flow through the front of a front line, so a, Double PCB b two-layer line of the probability of a small. The activity of the conductive ink screen printing is also very important to the carbon hole, the ink is viscous, the activity is poor, and the conduction probability of the base line is smaller. In the screen printing process, if the use of machine printing, operating table selection vacuum suction equipment is conducive to conductive ink activities, but usually simple to make ink residue in the operating table, Double PCB the residual ink is necessary to remove timely, otherwise affect the quality and beauty of the line, and even form a short circuit. If the use of technical printing, the operating table does not have a vacuum suction equipment, screen printing should be placed after a period of time after the PCB into the drying furnace dry, so that the conductive ink fully activities, so that two-layer circuit guide. Screen printing process to control the ink thickness to satisfy the requirements of the line resistance value.
4. Shape stamping and ultimately product inspection based on the usefulness of the circuit board, stamping forming a certain scale requirements of the shape. Test whether the circuit is short circuit, whether the circuit breaker and resistance value is not meet the requirements.