The basics of SMT/circuit board assembly.

1. August 13, 2013
Surface Mount Manufacturing Basics
Familiarization information for SMT printed circuit board
production

2. August 13, 2013page 2 /
SMT Production Processes
1. Screen Printing
2. Adhesives/Epoxy Dispensing (Optional)
3. Pick and Place
4. Reflow
5. Inspection Post-Reflow (Optional)
6. Secondary PCB assembly (Optional)
7. Cleaning (Optional)
8. Depaneling
9. Product Sub Assembly / Product Assembly
10.Testing
11.Packaging
12.Shipping

3. August 13, 2013page 3 /
Processes Defined
• Step #1 Screen Printing
– A bare PCB with all of the pads
for surface mount components is
placed into a screen printer
where solder, in a paste form, is
forced through a screen (with
artwork to match the PCB) and
onto the pads of the PCB.

4. August 13, 2013page 4 /
Processes Defined
• Step #2 Adhesives / Epoxy
Dispensing (Optional)
– A PCB with solder paste on the
pads has adhesive or epoxy
dispensed onto select locations.
– This is typically only used when
components are known to move
prior to reflow (MELFS) or more
commonly used to hold
components prior to and during
wave soldering.

5. August 13, 2013page 5 /
Processes Defined
• Step #3 Pick and Place
– The PCB with the solder paste
on the pads is presented to a
pick and place machine. This
machine picks up, inspects, and
places components onto the
solder paste.

6. August 13, 2013page 6 /
Processes Defined
• Step #4 Reflow
The PCB with components
basically on top of solder paste
enters the oven and is gradually
introduced to temperatures that
cause the solder paste to
become liquidous, once the
paste is liquidous, the parts
settle into the paste and make
electrical contact with the SMT
pads.
The result when the paste cools
as the PCB exits the oven is a
mechanical and an electrical
bond between the component(s)
and the PCB.

7. August 13, 2013page 7 /
Processes Defined
• Step #5 Inspection
(Optional)
– The inspection or AOI
(Automated Optical Inspection)
can be performed pre or post
reflow. This is typically an
automated machine that uses a
camera and verifies correct
component placement and
rotation.
– Pre-reflow inspection allows for
easier rework if needed

8. August 13, 2013page 8 /
Processes Defined
• Step #6 Secondary
Manufacturing / Insertion
– The SMT assembled PCB May
have pins, tabs, connectors or
other press fit type items
installed.
– This step is application
dependant and may happen pre
or post inspection, dependant
upon the final product and
custom application specifications

9. August 13, 2013page 9 /
Processes Defined
• Step #7 Cleaning
(Optional)
– The assembled PCB is run
through an aqueous cleaning
unit to ensure no contaminents
or flux reside is left on the PCB.
– This step is optional because a
“no-clean” solder may be used
whereas no cleaning is
necessary, many customers
clean PCB’s regardless of the
type of solder and flux used

10. August 13, 2013page 10 /
Processes Defined
• Step #8 Depaneling
– Individual images are depaneled
or separated from the multi-up
array by various means including
hand separation, breaking,
routing, or punching.
– This step is very often
overlooked even though the
PCB is complete and very
expensive at this point in the
manufacturing process.

11. August 13, 2013page 11 /
Processes Defined
• Step #9 Product
Subassembly / Assembly
– The assembled, depaneled
PCB is placed into a housing or
made part of the larger assembly
being built by the manufacturer
– This step is different depending
upon the product(s) being
manufactured

12. August 13, 2013page 12 /
Processes Defined
• Step #10 Testing
– The final product is tested
• Step #11 Packaging
– The final product is packaged for
shipment
• Step #12 Shipping
– The final product is shipped to
the end user, distributor, or
customer