00198574-01_Process_Foundation_DEK_Micron_EN - 第10页
3 Stencil Print 10 Process Foundation DEK Micron-Series 12/2017 Exercise ● Set up the printer to run a product ● Remove the squeegees and set the print pressure to 0kg ● Cycle a board from left to left ● Observe the ma…
3 Stencil Print
Process Foundation DEK Micron-Series 12/2017 9
3 Stencil Print
Introduction to Stencil Printing
●
What is the objective of the surface mount assembly process?
To provide a conducting path between the board (or substrate*) and components throughout
the designed life of the product.
●
What is the objective of the stencil print process?
To transfer the specified volume of material to the correct place on the board (or substrate*) at
the right time.
*Sometimes we print onto ceramic plates, PCBs (also known as PWBs – printed wire board), or
other things. The collective name for them is "substrate".
In addition we wish to achieve this objective at the required throughput with maximum yield and
minimum defects. The design of the product file and continued maintenance of the process is vital
in achieving this aim.
Stencil Print Process
1. Zero "Print Gap"
2. Controlled "Print Speed"
Even "Squeegee Pressure"
3. Board is lowered under controlled
"Separation Speed"
Stencil Print Theory
Squeegee Process
●
Transfer/ driving forces influenced by:
– Squeegee Angle
– Print Speed
– Paste Rheology
– Paste Roll Volume
3 Stencil Print
10 Process Foundation DEK Micron-Series 12/2017
Exercise
●
Set up the printer to run a product
●
Remove the squeegees and set the print pressure to 0kg
●
Cycle a board from left to left
●
Observe the machine as it carries out a print cycle
Number these actions in the correct sequence:
Camera Moves to Board Stop position Board exits machine
Tooling clearance check Board Stop is lowered
Fiducial positions are captured Board separates from stencil
Board travels to Board Stop position Stencil alignment completed
Press RUN Board is unclamped
Board is clamped in rails Board stop is raised
Camera homes Print stroke carried out
Board lifts to stencil
The Perfect Print
When inspected, a perfect print may have the
following features:
●
Straight and clean edges
●
Flat and even top surface
●
Consistent print height from pad to pad
and board to board
●
Good alignment – centralised on the pad
●
No flux bleed or print material out with the
deposit (i.e. solder balls)
3 Stencil Print
Process Foundation DEK Micron-Series 12/2017 11
Print Cycle
Critical Success Factors
The screen-printing process is a combination of many factors and variables and to ensure that the
process is successful in its aim, each of these must be kept in control.
The critical factors are: What control do I have over
these factors?
Process Hardware
●
Board (Substrate)
●
Tooling
●
Stencil Print Material
●
Squeegees
Process Parameters
●
Print Speed
●
Print Pressure
●
Separation Speed
Under-screen Cleaner
●
Settings
●
Performance
Environment
●
Temperature
●
Humidity
Machine Condition
●
Clean
●
Free From Damage
●
Machine accuracy
●
Machine repeatability
●
Machine regularly, ser-
viced and maintained
Training
●
Printer Staff Suitably
●
Qualified
This course will provide the knowledge required to keep these critical success factors in control and
thus maintain a robust process.
Exercise
Complete the table above. Next to each critical success factor, identify what control you have over
them i.e. do they fall directly under your area of responsibility, if there was a problem could you
simply change it or would you need to escalate the problem?