SIPLACE S-23 HM - 第193页
User Manual SIPLAC E S-23 HM 6 Vision functions Software Version SR.406.xx 02/00 US Edition 6. 2 PCB vision system 193 – Thick ness ( d) Y ou sho uld ensur e, particul arly with ti n fiducia ls, tha t a warpage of mo re …
6 Vision functions User Manual SIPLACE S-23 HM
6.2 PCB vision system Software Version SR.406.xx 02/00 US Edition
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Dimensions of the fiducials: Simple and double crosses 6
6
Fig. 6.2 - 3 Simple and double crosses with ideal dimensions
Key to Fig. 6.2 - 3
(1) Simple cross
(2) Double cross
6
The minimum dimensions for a fiducial in length (l) and width (b) depend on the line thickness (s)
and on the structure of the fiducial. 6
– Length (l) and width (b)
For the good fiducial recognition, the length and the width should be at least 0.9 mm with the
simple cross and 1.8 mm with the double cross. The ideal dimensions for the simple cross are
2.0 mm and for the double cross 2.75 mm. Under normal circumstances, length and width will
be equal.
– Line thickness (s)
The ideal line thickness for both fiducial types is 0.5 mm. The line thickness may vary, however,
according to standard structure widths and the type of fiducial. You should ensure that the line
is at least 0.3 mm thick, though.
– Line spacing (a)
Line spacing depends on the type of fiducial. Under no circumstances should line spacing fall
below 0.5 mm. For the double cross, the ideal spacing will be 0.75 mm.
l=2,75 mml=2,0 mm
b=2,0 mm
s=0,5 mm s=0,5 mm
b=2,75 mm
a=0,75 mm
2
1
User Manual SIPLACE S-23 HM 6 Vision functions
Software Version SR.406.xx 02/00 US Edition 6.2 PCB vision system
193
– Thickness (d)
You should ensure, particularly with tin fiducials, that a warpage of more than 1/10 of the struc-
ture width is not exceeded. If this degree of warpage is exceeded, the fiducial may not be
evenly illuminated. This would lead to variations in reflection characteristics and unwanted re-
flections. Recognition of the fiducials will then no longer be assured.
Recommended fiducial dimensions 6
Analysis of the fiducial shapes 6
For tinned and higher dimensional stable structures, (a low degree of etching variation) full circles
or full squares may be regarded as very satisfactory fiducial shapes (the ratio of fiducial thickness
to presoldering thickness will be large!). If dimensional stability falls, the full circle should be pre-
ferred to the square. 6
As far as the fiducial shapes of simple and double cross are concerned, bright copper is advanta-
geous as long as oxidation has not advanced too far. 6
– Surface of the fiducials
Make sure that the surface of the fiducial is as level as possible and with little oxidation. Avoid
wetting the fiducial with solder-stop lacquer as this could result in lowering the contrast with the
background or produce unwanted reflections. Similar effects occur with tinned fiducials as well.
– Contrast of the fiducials
To ensure that fiducial recognition is of a high quality, select a high brightness contrast between
the fiducial and the base material; in other words, bright fiducials on a dark base material and
vice versa. For example, on a copper or tin background apply dark fiducials. In the case of ce-
ramic substrates with a bright surface and unsatisfactory reflective properties, it is often helpful
to precoat with a dark resistance material in order to improve contrast characteristics.
– Number of fiducials
When using ceramic substrates and small boards, tow fiducials will usually be sufficient. How-
ever, with larger boards it is recommended that three fiducials be defined. The individual fidu-
cials can vary in structure. You can simplify the recognition procedure if you use the same
structure for each fiducial.
Fiducial type Simple cross Double cross
Range Ideal Range Ideal
Length (l) 0.9 mm (min) 2.0 mm 1.8 mm (min) 2.75 mm
Width (b) 0.9 mm (min) 2.0 mm 1.8 mm (min) 2.75 mm
Line thickness (s) 0.3 - 1.4 mm 0.5 mm 0.3 - 0.75 mm 0.5 mm
Line spacing (a) — — 0.5 mm (min) 0.75 mm
Thickness (d) < 1/10 of the structure width < 1/10 of the structure width
Tab. 6.2 - 1
6 Vision functions User Manual SIPLACE S-23 HM
6.2 PCB vision system Software Version SR.406.xx 02/00 US Edition
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– Correction with two fiducials x-position
y-position
PCB skew
– Correction with three fiducials: ideally, the straight lines which each pass through the cen-
ters of two fiducial will be parallel with the x and y axes
x-position
y-position
PCB skew
Shear
Warpage of PCB in the x direction
Warpage of PCB in the y direction
NOTE 6
You should never position 3 fiducials so that they are located on a straight line. 6
– Spacing between the fiducials
You may locate the fiducials at any point on the board. However, it is a good idea to space the
fiducials as far apart as possible on the two axes. The further apart the fiducials are from one
another, the more accurate optical position and angle recognition will be.