IT3/IT5
Connector System
T
IPS FOR
SMT
A
SSEMBLY
Document Number:
ETAD-F0458
Revision 3.10
Page
51
of
73
The SMT assembly process has many sources of variation, introduced by the equipment, the
components, the chemistries and the environment. Most common defects can have many
possible root causes located anywhere throughout the process. Please note that:
1)
Before making changes to the assembly process, it is very important to verify the root
cause(s) of defects.
2)
After making changes to the assembly process, it is very important to follow some
assemblies through the remainder of their production to make sure the changes do not
create other problems downstream.
Unless specifically mentioned, IT3 and IT5 share the same capability and requirement.
11.1 Stencil Printing
Of all the steps involved in and SMT assembly process, stencil printing has the largest influence
on overall yields. Therefore, getting a good quality stencil print plays a key role in a high quality
process. If print quality is not satisfactory, corrective action should be taken immediately.
System check:
The
first step
in investi ga ting pri nt quality problems is usually to
check the setup
of the printing s ys tem. A typi cal setup check would include:
1.
Observe the sol der paste
. Ensure the proper amount is on the s tencil – the diameter of
the bead should be approxi ma tel y 1.5cm. Watch it during the print stroke. It should roll
over the surfa ce of the s tencil , and should release cleanl y from the squeegee blade
when the blade li fts awa y from the s tencil . If the paste does not show this desi red
beha vior, remove i t from the s tencil and replace i t wi th fresh solder paste.
2.
Remove the stencil
from the printer and
check it for damage
, such as broken or
dis torted webs between the apertures in fine pitch a reas, or dents or deforma tions
anywhere in the foil
. Check the apertures
for debris
or residual solder paste.
Check the
fiducials
for wear or sol der paste smea rs .
Check the stencil’s mounting mesh
for rips or
tea rs .
3.
While the stencil is out of the printer, shuttle the boa rd into printing position.
Check its
underboard support
by gentl y pressing on the PWB wi th a finger.
Check its lateral
support
by tryi ng to move i t in the X a nd Y di rections
. Always wear gloves
when
handling ba re PWBs . If va cuum tooling is used, che ck i t for leaks.
4.
Reinstall the stencil
a nd moni tor its automa ti c alignment process . Wi th the s tencil in
pri nt posi tion (conta cting the PWB), visuall y
confirm that the a pertures and the pads
are properly aligned
. Ta p gentl y on the s tencil foil to confi rm solid conta ct between the
s tencil and the PWB.
There should be no gaps between the stencil and the PWB.
Section 11 Tips for SMT Assembly
Nov.1.2022 Copyright 2022 HIROSE ELECTRIC CO., LTD. All Rights Reserved.
