Solder Paste Printing Process
One of the most important process is " Solder Paste Printing Process " which 70 % of
SMT defect was cause of this process, the very important parameter, tools and design is the
things you can not ignore them.
Many engineer and technical guys is not enough focus on this importance of the
printing process which is the " Biggest Fault " because they will failed in the finding out the
root cause and you know that the root cause can bring the solution for your SMT process, I
can say that the best Solder Paste Printing Process Design can reduce your SMT defect more
than 70 %.
OK Let's try to study the principle of the process right now.
Main function of Solder Paste Printing Process is to print the solder paste on PCB pad /
foot print with the good shape as same as stencil design with the main parameter and tools
as below ....
Tools / Machine
- Solder Paste Printing Machine
- Stencil
- Squeegee blade
Material
- Solder Paste
- Glue / Adhesive
Operator (Man)
- High skill person : Need the high skill person to operated this work with the training
certificated.
How to print the solder paste onto the PCB pad
1.) Set the tool and M/C as below
- Set the squeegee.
- Set the supported pins.
- Put the stencil into the M/C.
- Bring the Solder paste to prepare by Stirling with manual or stirling M/C to make the solder viscosity is lower and remove the air bubble inside the solder paste.
- Put the solder paste onto the stencil.
2.) Load the printing program from M/C's recipe that Engineer / Technician already done.
Then do test print at the conversion time for 2 PCBs as below,
3.) Put the Hitalex (Thin film material for test print, transparent color) onto the PCBs for 2 PCBs
4.) Put the PCB on the conveyor , then the conveyor will bring the PCB to the printing machine.
5.) PCB will be stopped by M/C's stopper and then Clamp the PCB with the push up pin (supported pins) and the PCB will be pushed to touch the TOP CLAMP of the printing M/C, that's finish clamping.
6.) M/C's Camera will move to view the 2 fiducial marks on stencil.
7.) M/C's Camera will move to view the 2 fiducial marks on PCB.
8.) M/C table will start push up the table to touch with stencil (at the PCB's side of stencil).
9.) Squeegee will move down to touch on the stencil (at the Squeegee side of stencil) from front side then move to rear side , we call this as "Front Side".
10.) Stencil & PCB table is departed (removed)
11.) PCB will be loaded out from M/C.
12.) Technician / Engineer take a look the printing quality by visual eye and magnifier 3X up , inspect for below criterias
- Solder paste printing mis-alignment
- Solder paste shape must not smear / icicle / sharp at the top
- Solder paste volume must not be insufficient / no solder / exceed
13.) Bring the PCB to measure the solder paste thickness with some inspection M/C or SPI (solder paste inspection machine)
14.) Do from 3.) to 12.) for 2nd PCB with REAR SIDE test (print from rear to front side)
In case of the factory have SPI M/C (Solder Paste Inspection Machine) then do follow below,
15.) After print solder paste onto PCB then load the PCB to SPI M/C.
16.) SPI M/C inspect the PCB refer below criteria,
- Solder paste printing mis-alignment
- Solder paste volume (general spec about 50% - 170% of calculation from stencil design)
* Some factory identify spec about 50% - 150% , some identify as 50% - 170% that's depended on each factory policy.
- Solder paste area (general spec about 50% - 170% of calculation from stencil design)
* Some factory identify spec about 50% - 150% , some identify as 50% - 170% that's depended on each factory policy.
After finish conversion for 2 PCB , Quality already inspect these 2 PCBs and accepted already then we start mass run.
Also QC should have roving / sampling audit every 1 or 2 hour as factory's identification in the quality procedure and then identify the inspection criteria also.
Remark : Show pictures
Printing M/C
Squeegee
Stencil
Solder paste after printing
Zoom in : Solder paste after printing
Zoom in : Solder paste before printing.
END.
1.) Set the tool and M/C as below
- Set the squeegee.
- Set the supported pins.
- Put the stencil into the M/C.
- Bring the Solder paste to prepare by Stirling with manual or stirling M/C to make the solder viscosity is lower and remove the air bubble inside the solder paste.
- Put the solder paste onto the stencil.
2.) Load the printing program from M/C's recipe that Engineer / Technician already done.
Then do test print at the conversion time for 2 PCBs as below,
3.) Put the Hitalex (Thin film material for test print, transparent color) onto the PCBs for 2 PCBs
4.) Put the PCB on the conveyor , then the conveyor will bring the PCB to the printing machine.
5.) PCB will be stopped by M/C's stopper and then Clamp the PCB with the push up pin (supported pins) and the PCB will be pushed to touch the TOP CLAMP of the printing M/C, that's finish clamping.
6.) M/C's Camera will move to view the 2 fiducial marks on stencil.
7.) M/C's Camera will move to view the 2 fiducial marks on PCB.
8.) M/C table will start push up the table to touch with stencil (at the PCB's side of stencil).
9.) Squeegee will move down to touch on the stencil (at the Squeegee side of stencil) from front side then move to rear side , we call this as "Front Side".
10.) Stencil & PCB table is departed (removed)
11.) PCB will be loaded out from M/C.
12.) Technician / Engineer take a look the printing quality by visual eye and magnifier 3X up , inspect for below criterias
- Solder paste printing mis-alignment
- Solder paste shape must not smear / icicle / sharp at the top
- Solder paste volume must not be insufficient / no solder / exceed
13.) Bring the PCB to measure the solder paste thickness with some inspection M/C or SPI (solder paste inspection machine)
14.) Do from 3.) to 12.) for 2nd PCB with REAR SIDE test (print from rear to front side)
In case of the factory have SPI M/C (Solder Paste Inspection Machine) then do follow below,
15.) After print solder paste onto PCB then load the PCB to SPI M/C.
16.) SPI M/C inspect the PCB refer below criteria,
- Solder paste printing mis-alignment
- Solder paste volume (general spec about 50% - 170% of calculation from stencil design)
* Some factory identify spec about 50% - 150% , some identify as 50% - 170% that's depended on each factory policy.
- Solder paste area (general spec about 50% - 170% of calculation from stencil design)
* Some factory identify spec about 50% - 150% , some identify as 50% - 170% that's depended on each factory policy.
After finish conversion for 2 PCB , Quality already inspect these 2 PCBs and accepted already then we start mass run.
Also QC should have roving / sampling audit every 1 or 2 hour as factory's identification in the quality procedure and then identify the inspection criteria also.
Remark : Show pictures
Printing M/C
Squeegee
Stencil
Solder paste after printing
Zoom in : Solder paste after printing
Zoom in : Solder paste before printing.
END.
