PCBA Tech - PCB copy board negative film correction and terminal blocks

Five correction methods of negatives in the process of PCB copying

In the process of PCB copying, the negative film is often deformed, which is usually caused by improper temperature and humidity control or excessive heating of the exposure machine, which will affect the quality and performance of the PCB copying. The method of deforming the negative film.

1. Splicing method

is suitable for the film that is not too densely packed and the film deformation of each layer is inconsistent. It is particularly effective for the correction of the solder mask film and the film of the power layer of the multilayer board.

Specific operation: cut the deformed part of the negative film, re-splice the hole position of the drill test board, and then copy it. Of course, this is for simple deformed lines, large line widths and spacing, and irregularly deformed graphics; It is not suitable for film with high wire density, line width and spacing less than 0.2mm.

Warm reminder: When splicing, pay attention to as little as possible to damage the wires and not to damage the pads. When revising the version after splicing and copying, pay attention to the correctness of the connection relationship.

2. Change the hole position method

is suitable for the correction of the film with dense lines or the uniform deformation of each layer of the film.

Specific operation: first compare the negative film and the drilling test board, measure and record the length and width of the drilling test board respectively, and then adjust the hole position on the digital programming instrument according to the two deformations of the length and width., The adjusted drilling test board will cater to the deformed film. The advantage of this method: Eliminates the troublesome work of editing negatives, and can ensure the integrity and accuracy of the graphics. The disadvantage is that the correction of the negative film with very serious local deformation and uneven deformation is not effective.

Warm reminder: To use this method, you must first master the operation of the digital programming instrument. After using the programming instrument to lengthen or shorten the hole positions, you should reset the out-of-tolerance hole positions to ensure accuracy.

3. PCBpad overlap method

is suitable for film with line width and spacing greater than 0.30mm, and the pattern lines are not too dense.

Specific operation: Enlarge the holes on the test board into pads to overlap and deform the circuit piece to ensure the minimum ring width technical requirements.

Warm reminder: After overlapping copy, the pad is elliptical. After overlapping copy, the edge of the line and the disk will be halo and deformed. If the user has very strict requirements on the appearance of the PCB board, please use it with caution.

4. Photographic method

is only suitable for silver salt film. It can be used when it is inconvenient to re-drill the test board and the deformation ratio in the length and width directions of the film is the same. The operation is also very simple: just use the camera to enlarge or reduce the deformed graphics.

Warm reminder: usually the film loss is more, and it needs to be debugged many times to get a satisfactory circuit pattern. When taking pictures, the focus should be accurate to prevent the lines from being deformed.

5. Hanging method

is suitable for undeformed negatives, and can also prevent the negatives from deforming after copying.

Specific operation: Take the film out of the sealed bag before copying, and hang it in the working environment for 4-8 hours, so that the film has been deformed before copying, then after copying, the probability of deformation is very small NS. For the film that has been deformed, other measures need to be taken.

Warm reminder: Because the film will change with the change of the environmental temperature and humidity, when hanging the film, make sure that the humidity and temperature of the hanging place is the same as that of the working place, and it needs to be in a ventilated and dark environment to prevent the film from suffering Pollution.

Of course, the above are all remedies after the film is deformed. Engineers should still consciously prevent the film from deforming. In the PCB copying process, the temperature is usually strictly controlled at 22±2°C, and the humidity is at 55%±5%RH. Use cold light source or aerator with cooling device, and constantly replace the backup film.

Four categories of PCB terminals

PCB terminals are mainly divided into four categories: pluggable terminal blocks, screw terminal blocks, spring terminal blocks, and barrier terminal blocks.

The first category: pluggable terminal blocks

The product has a pin pitch of 3.5, 3.81, 5.0, 5.08, 7.5, and 7.62 with a pole number of 2-24 lines. It can provide a screw-fixed socket for matching and anti-vibration connection. The plug uses side connection technology, that is, the direction of the screw is perpendicular to the direction of the wire.

The second category: screw terminal

The circuit board terminal has always occupied a very important place in the electronics industry, and has now become an important part of the printed circuit board. Its structure and design are more sturdy with the characteristics of convenient wiring and reliable screw connection; compact structure, reliable connection, and its own advantages; use the lifting principle of the clamping body to ensure reliable wiring and large wiring capacity; welding feet and clamping wires The body is divided into two parts to ensure that the distance when the screw is tightened will not be transmitted to the solder joint and damage the solder joint; the shell is strong and reliable, and the stitch pitch is accurate.

The third category: spring-type printed circuit board terminals

Spring-loaded printed circuit board terminals are provided with equal spacing of 2.54mm, 3.50mm, 5.00mm, 7.50mm, 7.62mm; single-core wires can be inserted directly without the aid of a handle, but smaller wires can be opened and clamped by the handle Wire clamping; no button specification, so that the height can be greatly reduced, the wire can be easily taken out by pressing down with a screwdriver when the wire is retracted; most of the spring-type terminals are combined piece by piece; the wiring method is very suitable for communication systems, Lighting system, monitoring system and building wiring; various wiring directions, easy to assemble in a small space, can be combined with any number of contacts, easy to operate, suitable for high-density wiring needs.

The fourth category: Barrier PCB terminal blocks

The fence type code is LW; the middle needle position code is C; the side needle position code is B; the fixed position code is M; the curved needle type code is R; the wire bonding code is Q; the LW fence type product has a simple structure and plate type The crimping method is intuitive and firm; the wire diameter range: 0.5m-6m.