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36 Vision Sensor Technology PCB Position Recognition Fiducial criteri a Loca te 2 fi ducia ls Loca te 3 fi ducia ls X-/Y-position, r o tation angle, mean PCB distortion in addi tion: shear , distortion in X- and Y-direct…

Vision Sensor Technology

PCB Position Recognition

Technical data

PCB fiducials

Local fiducials

Library memory f. recogni-

tion of bad panels

up to 3 (subpanels and multiple

panels)

up to 2 per PCB (may be of dif-

ferent type)

up to 255 types of fiducials per

subpanel

Image analysis Edge detection method (geo-

metric alignment) based on

gray-scale values

Lighting method Front lighting

Fiducial recognition time 0.4 s

Field of vision 5.7 x 5.7 mm

Camera’s field of view

Pixel

Ink spot, e.g. square

Evaluation window

Geometrical Alignment

With these data the PCB

vision module is able to

search and recognize the

fiducial at the predefined

position on the PCB or ceram-

ic substrate without further

assistance. For this reason it

places several small evalua-

tion windows at the assumed

border of the fiducial. Within

these evaluation windows

the vision system looks for

contrast transitions between

bright and dark. After finding

such contrasts the actual

position of the fiducial can be

assigned by comparison with

the predefined – and thus

known – shape and size.

The analysis operations can

be used to determine any off-

set with respect to the

DESIRED position in the X and

Y directions and the angular

position.

Saving the fiducial by teach-

ing is not necessary any

more.

Additional functions of the

PCB vision module are recog-

nition of the position of the

feeder modules and ceramic

substrate (optional) and

recording of the machine

data including mapping.

The bad board detector

(GOOD/SCRAP scan) is also

moved over the ink spot

using the PCB vision module.

Description

SIPLACE has a number of

vision modules and a central

vision system to evaluate the

recorded image data ensur-

ing high placement accuracy.

At the machine's X-gantry

the PCB vision module is

mounted. It is used to find

the PCB's positioning-offsets

within the conveyor system.

This vision module is also

required to measure the

machine origin and/or the

feeder module positions on

one side of the table. Each

vision module consists of a

single CCD camera with inte-

grated lighting and optics.

The offsets in the position of

the PCBs are determined with

the help of at least two but

generally three reference

fiducials on the PCB. When

the PCB arrives at the place-

ment area the positioning

system with its PCB vision

module moves to the pro-

grammed fiducial.

The edge detection method

allows to choose predefined

fiducials from a menu (e.g.

cross, circle, square). The size

of the fiducial is programmed

at the station computer.

From this time on form and

size of the fiducial is defined

and known.

Vision Sensor Technology

PCB Position Recognition

Fiducial criteria

Locate 2 fiducials

Locate 3 fiducials

X-/Y-position, rotation angle,

mean PCB distortion

in addition: shear, distortion in X- and

Y-direction separately

Fiducial shapes Choose synthetic fiducials from the

menu: circle, cross, square, rectangle,

rhombus, circular, square, and rectan-

gular contours

Fiducial surface:

Copper

Tin

Without oxidation and solder resist

Warp ≤ 1/10 of structure width, both

with good contrast to environment

Fiducial dimensions:

Circle

Cross

Rectangle/square

Rhombus

Diameter: 0.3 - 3 mm

Length and width: 0.3 - 3 mm

Line thickness: 0.1 - 1.5 mm

Edge length: 0.3 - 3 mm

Diagonal: 0.3 - 3 mm

Fiducial environ-

ment

Clearance around reference fiducial

not necessary if there is no similar

fiducial structure in the search area

Teach Synthetic Fiducial

Description

Different fiducial shapes

prove to be optimal depend-

ing on the condition of the

surface.

Particularly advisable for bare

copper surfaces with little

oxidation is the single cross.

Maximum recognition reli-

ability is achieved due to the

high information content.

Rectangle, square and circle

are less “informative” but

save space, are rugged, and

can even be used when oxi-

dation is at an advanced

stage.

Advisable for tinned struc-

tures are circle or square

because in this case the ratio

of the fiducial dimensions to

the presolder thickness is

particularly favorable.

Fiducial editor

Vision Sensor Technology

Bad Board Recognition

Position Recognition for Feeder Modules

Ink Spot Criteria

Evaluation method

for fiducials

for structures

brightness method

contrast method

Shapes and sizes of fidu-

cials/structures for

brightness method

contrast method

square or circular forms

edge length / diameter 0.3

to 5 mm

rectangular shapes

edge length: 0.3 to 5 mm

Masking material mat dark (light-absorbing)

not recommended: white or

shiny

Recognition time 0.3 s for each method

Description

In the cluster technology

each subpanel is assigned an

ink spot. If this is present dur-

ing the measurement via the

PCB vision module, the corre-

sponding subpanel is popu-

lated.

It is also possible to accom-

plish the population of the

subpanel when the ink spot is

missing. With this function it

is possible to eliminate costs

due to unnecessary popula-

tion of faulty subpanels.

Global Ink Spot

Each GOOD/SCRAP scan takes

some time, and the time

required is even greater if

there are a large number of

subpanels on a PCB. Using

the global ink spot can result

in a significant reduction of

these secondary times.

The PCB vision module

searches at positions taught

before for the defined fidu-

cial. In case of recognition

there is no following evalua-

tion of subpanels. The sys-

tem allows the operator to

choose also the reverse inter-

pretation.

Recognition of the position

of the feeder modules

The pick-up position of the

components can be deter-

mined precisely with the aid

of the position recognition

for the feeder. The offset in

position relative to the stored

ideal position is determined

on the basis of fiducials on

the feeder modules using the

PCB vision module. This pro-

vides a very high pick-up reli-

ability even for the very first

component. This is particu-

larly important for small com-

ponents.