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5 Product File and Machine Setup 5.6 Set up Basic Process Parameters to Ensure Acceptable Quality Prints Process Foundation DEK Micron-Series 12/2017 37 Separation Distance This should be the minimum required to allow th…

5 Product File and Machine Setup

5.6 Set up Basic Process Parameters to Ensure Acceptable Quality Prints

36 Process Foundation DEK Micron-Series 12/2017

5.6 Set up Basic Process Parameters to Ensure Acceptable

Quality Prints

Print Speed and Pressure

Print speed and print pressure are directly related…

1. As speed

2. Pressure should go

Increasing speed requires a corresponding increase in pressure in order to maintain the same print

results. This leads to accelerated squeegee and stencil wear.

Print Speed

Print speed should be selected according to the material manufacturer’s guidelines. The printer

output must keep up with the demands of the line, which in turn should be ‘balanced’ to match the

slowest stage. There is often no benefit in running the printer at high speeds if the boards are to

wait on the conveyor for a long time. If cycle time is not critical then generally the lowest print

speed is selected as this normally creates the least problems. On the other hand print speed may

be increased to create time for other functions, i.e. under-screen cleaner, vision inspection.

●

Squeegees, start slow, around 20mm/s (typical: 20-50mm/s*)

●

Match the line beat rate

●

Balance with print pressure

●

Consult material manufactures data sheet

*If high speed pastes are used, refer to manufactures guidelines.

Squeegee Print Pressure

The general rule is to select the lowest pressure that just cleans the stencil surface. Print speed

and pressure are closely related so the pressure value should be adjusted to compensate for any

speed change. For instance, if speed goes up the pressure must also go up to ensure a clean sten-

cil.

Pressure above that necessary to clean the stencil should be avoided since it does little to improve

print quality or aperture fill, and will accelerate wear and tear of squeegee and stencil. With metal

blades, it can change the attack angle leading to process variation; with polyurethane blades it can

lead to scavenging of paste from the apertures.

If the boards to be printed suffer from warp then pressure may need to be increased to ensure a

flat surface and good gasket. Choosing stiffer squeegee blades can also help this.

As low as possible to clean stencil

Too low: Too high:

●

Excess print height

●

Scavenging

●

Incomplete print

●

Bridging

●

Excess stencil/ squeegee

Separation Speed

With most pastes there will be little difference to the print quality between slow and high separation

speeds. In most cases the maximum speed of 20mm/s is fine. If, however, deposits appear conical

or "dog eared" this may indicate that the speed needs to be adjusted. Paste viscosity, aperture size

and stencil manufacturing method are all factors that may determine the best separation speed. It

is difficult to predict what effect changing the separation speed will have on the print so experiment-

ation is vital. It should be noted that separation speed could have a large effect on the print cycle

time.

5 Product File and Machine Setup

5.6 Set up Basic Process Parameters to Ensure Acceptable Quality Prints

Process Foundation DEK Micron-Series 12/2017 37

Separation Distance

This should be the minimum required to allow the paste to clear the stencil at the programmed

separation speed. If the separation speed is set to maximum, then the distance doesn’t really

matter so should be set to its lowest value. If the separation speed is slow then the separation

distance should equal the stencil thickness plus a little extra to account for any stencil stretch.

Again, this parameter could have a large effect on the cycle time.

Print Gap

This should always be set to zero when using solder paste. There are other applications that do

use a gap, for instance: adhesive or ink printing. Refer to the appropriate applications training

modules for details.

Exercise

The objective is to edit the product file to be capable of printing five consecutive boards at the print

speed stated below with each board exhibiting zero print defects.

Note: At this stage there are no overheads to be considered from under-screen cleaning, vision

inspection, etc.

Determine, through experimentation, the best print parameter settings to successfully achieve the

objective. Record your results in the table below:

Squeegees

Print Speed 20mm/s

Squeegee Pressure

Separation Speed

Separation Distance

Notes:

………………………………………………………………………………………………………………

5 Product File and Machine Setup

5.6 Set up Basic Process Parameters to Ensure Acceptable Quality Prints

38 Process Foundation DEK Micron-Series 12/2017