The melf category is typically used for surface mount Melfs (Metal Electrode Leadless Face ). Melf Diodes are cylindrical glass or plastic packages that have metallized terminals at each end of the body. Melfs

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Application Notes – Melf Category
What classes of SMD components is this category used for?
The melf category is typically used for surface mount Melfs (Metal Electrode
Leadless Face ). Melf Diodes are cylindrical glass or plastic packages that have
metallized terminals at each end of the body.
Melfs come in a variety of sizes and are frequently size-matched to standard
SMD chip sizes (e.g. 0603, 0805).
The melf algorithm can also be used for certain components that do not conform
well to other UIC categories. Examples of these types of components are
provided later in this document.
In general, the melf algorithm is used for irregular components that do not require
extreme accuracy. It is advisable to try the chip algorithm first since this
approach tends to provide better accuracy.
In general terms, how does the algorithm work?
The algorithm performs image processing to determine the presence of a melf.
The algorithm then fits an ellipse to the image of the melf and extracts the end
points of the device along the major axis of the ellipse. The center of the melf is
defined to be the midpoint between the ellipse end points. The angle of the melf
is defined to be the angle of the major axis of the ellipse.
Melf recognition. Note that
this process takes place
internally and is not visible
during normal operation of
the machine.
51030001, Rev C
Melf centering, Standard Accuracy

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Does the melf algorithm have a High Accuracy mode? How
does it work?
A new high accuracy melf algorithm was introduced in UPS+ 6.1.x. The
algorithm was designed specifically for Melf devices because of the typical poor
image quality associated with them. The rough position is found, then a bounding
box of minimized area is placed around the found features. The position and
rotation of the bounding box determines the reported position and rotation of the
device.
I’m running UPS+ 6.1 and I’ve created a new melf definition.
Why isn’t there an Inspection Type selection on the Vision tab?
The accuracy mode is normally controlled through the Inspection Type field of
the component definition (Vision tab). In UPS+ 6.1.x, this field is not exposed
when you create a new melf. The Inspection Type field for melfs will be included
in the component definition as of UPS+ 6.2 (See below).
In UPS+ 6.1, use the following workaround to turn on high-accuracy melf
processing:
• Create a new chip definition (the Inspection Type is always exposed for a
new chip).
• From the Vision tab of the component definition, change the Centering Type
to melf and set the Inspection Type to High Accuracy.
UPS+ 6.2 Users:
Here is a machine image of a melf
being centered in High Accuracy
mode.
At vision diagnostic level 5, the
graphics display for high accuracy
melf processing shows outlines as
opposed to the green thresholding
displayed with standard accuracy.
No workaround is required in UPS+ 6.2: To run with High
accuracy, create a new melf definition and change the
Inspection Type to High Accuracy in the Vision tab of the
component definition.
New melf Vision tab for UPS+ 6.2
Melf centering, High Accuracy

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Should I choose High Speed or High Accuracy?
Here are the advantages (+) and disadvantages (-) of the Inspection Type
settings:
High Speed
+ Faster vision processing
– Looser dimensional tolerances
+ Dimensional tolerances are fixed
High Accuracy
+ Improved accuracy, robustness
– Slight degradation in vision processing speed
– Dimensional tolerances are programmable in UPS+ 6.2
In typical applications, melfs are not the dominant component on the circuit
board. In this type of scenario, High Accuracy is a good choice since it provides
a more accurate correction and supports programmable tolerances.
If speed is a concern and the image quality is good (high contrast, lack of
background noise), High Speed can be chosen.
Note: High Speed and High Accuracy inspection types should not be confused with the Accuracy
selection in the Heads tab of the component definition. This selection refers to the speed at
which the machine runs when placing the component.
How dimensionally tolerant is the algorithm?
The dimensional tolerance of the melf algorithm depends on the Inspection Type
chosen in the Vision tab:
High Speed
• The length tolerance is set at ±35% of the programmed length of the melf.
• There is no width tolerance check.
High Accuracy
• UPS+ 6.1: The tolerance is set exactly as in the High Speed case.
• UPS+ 6.2: The length and width tolerances are taken from the tolerance fields
of the component definition.
High Accuracy melf – dimensional tolerance in UPS+ 6.2
By default, when you create a melf definition, default dimensional tolerances are
set according to the following rules:
Let D = The programmed length or width of the melf
Small melf case: D < 0.015” (rare)
The tolerance for this dimension is set to ±20%
Larger melfs: D > 0.015”
The tolerance is at most 35% and is capped at ±0.015”.

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Examples:
Melf Type Length (0.001“) Width (0.001“) Length Tolerance (%) Width Tolerance (%)
0201 20 10 ±35% ±7-mils ±20% (W < 15-mils)
0402 40 20 ±35% ±14-mils ±35% ±7-mils
1206 120 60 12.5% ±15-mils* 25% ±15-mils*
* Default tolerance % driven by ±0.015” cap.
When you program a melf using the High Accuracy Inspection Type, the
database dimensional tolerances are used for size checking.
The melf dimensional tolerances can be changed in the same manner as chips.
To access the tolerances, select the Next… button on the Body tab of the melf
definition:
The tolerances can be changed in the range of 1 – 100%.
NOTE: Care should be taken in programming large tolerances as this can lead to
the possibility of a wrong-sized part being placed on the board.
How small a melf can the machine handle?
The answer to this question depends on the camera used to center the melf.
The vision system requires a minimum of 12 pixels x 6 pixels to accurately center
a leadless component. The table below lists several camera types and the
minimum melf size supported based on the minimum pixel requirement.
Camera
Minimum Melf Length
(12 pixels)
Minimum Melf Width
(6 pixels)
Magellan 2.3 mil/pixel 0.028” 0.014”
FlexJet 1.1 mil/pixel 0.014” 0.007”
HSC 0.8 mil/pixel NFOV 0.010” 0.005”

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What types of nozzles do I use for melfs?
Melfs require nozzles that conform to their cylindrical shape. There are several
melf nozzles available for each UIC head type. Contact your UIC Applications or
Field Engineer for nozzle recommendations for specific components
Are there other programming considerations with melf nozzles?
Yes. Since melf nozzles are not axially symmetric, you must define the Body
Length and Body Width to match the 0° shape of the nozzle.
For example, the 0° shape of a melf nozzle tip is shaped to pick a melf with its
long axis oriented along the x-axis of the machine. So in this case, you program
the melf with a Body Length greater than the Body Width:
In addition, it is important that you turn off APU for melf components. Since the
melf nozzle is designed to conform to the shape of the device, APU is not
needed. To turn off APU for components using melf nozzles, uncheck the APU
checkbox in the Heads tab of the component definition:
Example of a melf nozzle:
FlexJet 1340 nozzle.

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Turn off APU for all heads picking components using a melf nozzle.
Do I have to teach melf tape feeders?
We recommend using melf nozzles to pick melf components. Since the nozzle is
shaped to fit the particular melf being picked, teaching the feeder (or at least
verifying the pick position) is a good idea.
Can the vision system tell me how large the melf is?
For UPS+ 6.1 and higher, the answer is yes. Follow this general procedure:
1. Pick up a melf in Enhanced Component Setup. The programmed size should
be reasonably close.
2. Inspect the melf. If the melf happens to pass inspection or fails inspection
due to the size being out of tolerance, the Retrieve Observed button is
enabled in the ECS options section.
3. Select the Retrieve Observed button. The perceived size of the melf from the
vision system is returned to the component definition.

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The melf algorithm seems very flexible. Are there any risks
associated with it?
There are some risks associated with the melf algorithm. In standard accuracy
mode, the melf algorithm can be extremely forgiving and can be used to locate
many devices that otherwise would not be located using the chip algorithm. This
flexibility can also lead to poor centering performance with images that contain
background noise (e.g. overhanging reflective nozzles, contaminated nozzles).
For both standard and high accuracy melf processing, the algorithms are
intended to locate components anywhere in the field of view where the spindle is
completely obscured. Overhanging reflective nozzles such as those found on
HSC machines will affect the accuracy of the algorithm.
If you are using the melf algorithm to center melf devices, the specially designed
nozzle will not be visible in the image. The overhanging nozzle risk is more of a
factor in scenarios where the melf algorithm is used on devices that are not
actually melfs.
In both modes, depending on the component and nozzle sizes, there is the
possibility of finding an empty nozzle. The risk of this is highest in Standard
Accuracy mode where the inspection tolerances are loose.
What are the typical vision failure modes for melf centering?
“Major/minor dimension out of range”
One of the most prevalent failure modes for melf inspection is “major/minor
dimension out of range”. In some cases, the melf is simply dimensionally
misprogrammed. If this is the case and the failure is repeatable, use the Retrieve
Observed option in Enhanced Component Setup to capture the perceived melf size
from the vision system. Note that the perceived size depends on several factors
including light type and intensity, component geometry (rounded edges/corners), and
metallization.
In other cases, the dimensional failure can be caused by contamination on the
nozzle. In the image below, a component is being centered using the high
accuracy melf algorithm. Contamination on the nozzle is causing the algorithm to
fail with a dimensional error.
Contamination
Things to try…
• Clean the nozzle
• Do not use excessive light levels
• For non-contamination scenarios, use
ECS Retrieve Observed to ensure that
the programmed size is close to the
perceived size

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Dirty nozzle skew
Standard accuracy melf processing is susceptible to skewed centering as a result
of nozzle contamination. Consider the following image:
Nozzle being found as a melf
As mentioned earlier, one of the risks of the melf algorithm is recognizing a bare
nozzle as a component. Keep in mind that the risk of a nozzle being recognized
as a component depends on the programmed size of the component compared
to the size of the nozzle, and the tolerance of the algorithm.
The standard accuracy melf algorithm is particularly susceptible to this error due
to its fixed and loose dimensional tolerances.
The high accuracy melf algorithm is also susceptible as the image below
illustrates (the red box indicates the programmed size of the component):
The good news is that in UPS+ 6.2, dimensional tolerances are programmable
for the high accuracy melf algorithm.
Contamination
Contamination on the shoulder of the nozzle is
leading to a skewed correction.
Things to try…
• Clean the nozzle
• Do not run with excessively large search areas
• Do not use excessive light levels
• Consider using High Accuracy mode
HSC nozzle being centered with the high
accuracy melf algorithm.
Things to try…
• To help filter out empty nozzles
being centered as a component,
use the high accuracy mode.
• Reduce your dimensional
tolerances until the nozzle fails
inspection.

9. J. Herman 9 8/30/05
What other types of components can be centered the melf
algorithm?
Our preliminary experience with the high accuracy melf algorithm has shown it to
be an effective tool with components that do not fit nicely with other component
categories. Examples below include a coil with irregular shaped leads and an
LED with a non-rectangular outline.
User Notes:
Coil: FJ 2.6-mpp, melf centering type, High Accuracy LED: FJ 2.6-mpp, melf centering type, High Accuracy