Stamping Process
The epoxy stamping is a rather old technique to apply
an adhesive paste on a substrate. Due to the continuous
search in improving productivity and throughput,
stamping has recently gained more consideration.
The paste is placed into a rotating cup or plate which
surface is leveled by a blade set at the required height,
typically 0.3mm. During the dipping, the tool will collect
an amount of paste which depends on the tool geometry,
the speed, the height of epoxy layer and on the viscosity
and thixotropy of the paste. During stamping, a portion
of the collected paste will wet and stick on the target.
There are multiple stamping tool designs used to cover
the die size range. A few are here illustrated :
Daub Round Rectangle Star Grid Rubber Grid
The material is usually stainless steel or rubber pad for
the last one. Occasionally, a tool is made in tungsten
carbide. Other tip configurations are seen in production
floor like : Frame, Ring, Fork etc.
Stamping Recommendations
The stamping results are not easy to anticipate as there
are a lot of factors coming into play during the process.
By following some guidelines, we can approach the
desired results. Optimization is usually reached by
bond head stamping parameter adjustments or tool
dimensions tuning. The ability of the epoxy paste to wet
the back side of the die after placement���������������� will also help
to compensate small defects. The
example below is showing the epoxy
stamping layout of a STAR tool
4x2mm. After placement, the epoxy
does first not cover completely the
die but after a few minutes it slowly
expands through capillary effect. The
last picture is showing the die from
the top after curing. The wetting has
covered 100% of the die surface with
no excess of fillet on the four sides. We propose the
following recommendations concerning the choice of
tool based on the die size and a viscosity of 6000-12000
cps to be considered as medium :
13
DIE BONDING TOOL OVERVIEW
Die Size Tools
< 0.3mm DAUB
< 0.8mm ROUND
< 7x7mm STAR
> 7x7mm GRID ( steel or rubber)
The optimum size of the stamping tool is a priori not
easy to define due to the many variables involved in the
process. What complicates further the selection is the
non linearity of the any formula related to the die size
or ratio and paste viscosity.
Another problem is the limited quantity of paste that can
be collected by a tool to allow one stamping cycle and
get enough epoxy Bond Line Thickness. This is particular
problematic for large die sizes using the GRID tool type
or other SEST where a Stand Off Pin is not present or
not possible to manufacture.
Die Bonding tools
overview

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Note added at 11 jours (2013-07-13 21:30:22 GMT) Post-grading
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Merci !