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Analysis of negative deformation in PCB process
Nov 29, 2018

I. reasons and solutions for film deformation:

The reason:

(1) failure of temperature and humidity control

(2) the temperature rise of the exposure machine is too high

Solutions:

(1) usually the temperature control in 22 + 2 ℃, humidity in 55% + / - 5% RH.

(2) use cold light source or exposure machine with cooling device and constantly replace the backup negative

Ii. Process method of film deformation correction:

1, in the mastery of digital programming instrument operation technology, the first film and drilling test board, two deformation measure its length, width, on the digital programming device according to the deformation on a long or shortening, the size of the hole, it with long or shorten the hole after drilling test plate to be close the deformation of the film, splicing of film from all the work, to ensure the integrity of the graphics and accuracy.Call this method "change hole position method".

2, in view of the negative changes with the environment temperature and humidity changes of the physical phenomenon, take a copy of the negative before the film will be out of the film in the sealed bag, under the working environment conditions for 4-8 hours, so that the negative in the copy before the first deformation, so that the copy of the negative deformation is very small, said this method "hang method".

3. For graphics with simple lines, wide lines and large spacing and irregular deformation, the negative deformation part can be cut open and the hole position of the control drilling test plate can be reassembled and then copied, which is called "splicing method".

4. The hole on the test plate is enlarged into the line piece of the welding plate deforming to ensure the minimum ring width technical requirements. This method is called "welding plate overlap method".

5, the deformation of the negative graphics scaled up, re-mapping plate making, called this method "mapping method".

6, the use of a camera to enlarge or reduce the deformation of the graphics, called the "photographic method".

Iii. Matters needing attention in relevant methods:

1. Splicing method:

Applicable: line is not too dense, the film deformation of the film layer is not consistent;It is especially suitable for the deformation of soldering film and multilayer plate power source formation film.

Not applicable: film with high wire density, wire width and spacing less than 0.2mm;

Note: the wire should be cut as little as possible, do not damage the welding plate.Splicing copy of the revision, should pay attention to the correctness of the connection.

2. Change hole position method:

Applicable: all layers of film deformation is the same.The same applies to film with dense wiring;

Not applicable: film deformation is not uniform, local deformation is particularly serious.

Note: after the programming instrument is used to lengthen or shorten the hole position, the out-of-tolerance hole position should be reset.

3. Hanging method:

Apply;Negatives that have not yet been deformed and that prevent deformation after copying;

Not applicable: distorted negative.

Precautions: hang the film in a ventilated and dark (safe or not) environment to avoid contamination.Make sure that the hanging place is consistent with the temperature and humidity of the working place.

4. Pad overlap method:

Applicable: graph line is not too dense, line width and spacing is greater than 0.30mm;

Not applicable: in particular, users have strict requirements on the appearance of printed circuit board;

Note: due to overlapped copies, the welding disc is oval.After overlapping copies, line, disk edges of the halo and deformation.

5. Photography:

Applicable: the length and width of the film deformation proportion is the same, inconvenient to drill the test plate, only silver salt film.

Not applicable: film length and width direction deformation is not consistent.

Note: the focus should be accurate when taking photos to prevent line deformation.Film loss is high, usually, there is a number of debugging before the satisfactory circuit graphics.