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Solution for Negative Film Deformation of PCB Technology

by: Jul 25,2019 1409 Views 0 Comments Posted in Engineering Technical

Deformation. PCB Negative Film

The reasons for the deformation of the negative film and its solution: 

The reason:

(1) Temperature and humidity control failure

(2) The exposure machine temperature rises too high

Solution:

(1) Normally, the temperature is controlled at 22 ± 2 ° C and the humidity is at 55% ± 5% RH.

(2) Using a cold light source or an aerator with a cooling device and constantly replacing the backup film

 image.png

The process of negative film deformation correction:

 1.    Change the Hole Position Method

In the case of mastering the operation technology of the digital programmer, firstly, compared the negative film with the drilling test plate and measure the two deformation amounts of length and width. On the digital programmer, lengthen or shorten the hole position according to the amount of deformation, and use the drill test plate which has been lengthen or shorten the hole position to fit the deformed negative film. This way eliminates the tedious work of splicing the film and ensures the integrity and accuracy of the graphic.

2.    Hanging Method

Against the physical phenomenon that the negative film changes with the change of temperature and humidity of the environment, adopt to take the negative film in the sealed bag before copying the negative film, and hang it for 4-8 hours under the working environment condition, so that the negative film is deformed before copying, so that it will make the negative film very small  after copying.

 3.    Splicing method
For the pattern with simple line, wide line width and large spacing, and irregular deformation, the deformed portion of the negative film can be cut and then re-spliced against the hole position of the drilled test plate before copying

4.    Pad Overlap Method

Use the hole on the test board to enlarge it to the pad size and remove the deformed line piece to ensure minimum loop width technical requirements.

5. Texture method

Proportionally enlarge the graphic on the deformed film, and re-lay the plate

6. Photographing Method

Use the camera to enlarge or reduce the deformed figure.

 image.png

Notes of these relevant methods

1. Splicing method:

Applicable: the film with less dense lines and inconsistent film deformation of each layer; especially suitable for the deformation of the solder mask and multilayer power supply ground film;

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

Note: When cutting, try to minimize the damage to the wire and not damage the pad. When splicing and copying, you should pay attention to the correctness of the connection relationship.

 2. Change the hole position method:

 Applicable: The deformation of each layer is consistent. Line-intensive negative films are also suitable for this method;

Not applicable: The film is not uniformly deformed, and the local deformation is particularly serious.

Note: After using the programmer to lengthen or shorten the hole position, the hole position of the tolerance should be reset.

 3. Hanging method:

 Applicable; a film that has not been deformed and prevents deformation after copying;

Not applicable: Deformed negative film.

Note: Dry the film in a ventilated and dark environment to avoid contamination. Make sure that the air temperature is the same as the temperature and humidity at the work place.

 4. Pad Overlap Method

Applicable: The graphics lines are not too dense, and the line width and spacing are greater than 0.30mm;

Not applicable: In particular, the user has strict requirements on the appearance of the printed circuit board;

Note: After the overlap, the pads are elliptical, and the halos of the lines and pad edges are easily deformed.

5. Photo method

Applicable: The deformation ratio of the film in the length and width direction is the same. When it is inconvenient to use the heavy drill test board, only the silver salt film is applied.

Not applicable: The film has different length and width deformation.

Note: Focus should be accurate when shooting to prevent line distortion. The loss of the film is large. Under normal circumstances, it is necessary to have multiple adjustments to obtain a satisfactory circuit pattern.

 

 


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