Pick & place

An import step in the assembly process is placing the components on the board and for Surface Mount Devices (SMD) this is done with an automated Pick & Place machine.Using automated Pick & Place machines is much faster and more accurate than a manually placement of the surface mount components.Such machine have automated registration and super fast component placement with built in checks that use a variety of cameras.

Introduction for pick & place machine

For our Pick & Place machine to populate an assembly, we need some advanced preparation.First we upload the population program to the Pick & Place machine – this is based on the board layout – the BOM (bill of materials) and CPL (Component Placement List, also known as the Pick & Place file) to the Mycronic Mycenter workstation.

We also load the Pick & Place with previously kitted components.
The boards are printed with solder paste and the paste deposit is inspected by our Automatic Solder Paste Inspection machine also known as SPI.Surface mount devices or SMD component parts usually arrive in tape, tube or tray format.For tape components we use feeders, different size feeders for different width tapes.

Figure 1:feeders

Figure 2:feeder

The feeder magazine has a small pin which indexes the tape to the next position to present the next component for pick up.Tubes go into a “shaker”, which shakes the component inside the tube forward to the correct pick up position.

Figure 3:shaker

Finally, trays have fixed outer dimensions, but the inside layout can vary based on the part. Our machines can manage up to 8 of these trays at a time.One MY300 machine has 10 magazine slots in total. If we use all of them with 8mm tape components, we can mount 160 different components on one machine.This is the theoretical maximum, depending on the types of components selected, for a typical board we mount approximately 90-100 unique components on one machine.

Our Pick & Place machines are scalable and therefore if more unique placements are needed to be assembled on one board, we can use a line with two connected Pick & Place machines to double this number.

All the feeders, tubes and trays have an identification chip and a barcode.

Components get a unique identification barcode which contains a lot of information about the component including the (Manufacturers Part Number) MPN, quantity and size and other geometric and electrical information.

The barcodes of components and feeders are linked together during the kitting process. We can place these parts anywhere on the machines, the chip in the feeder tells the machine which component is where.

Placement accuracy is essential and the Pick & Place machine uses 3 fiducial points to locate the panel and determine the orientation.

If there are multiple boards on one panel, each individual PCB has its own local fiducials. The fiducials are optical targets that are etched in the copper layer of every board.The Pick & Place machine has a single pick up head and multi-head mounter. The single head is slower, but can grab different shapes and heavy parts.A multi-head can grab 8 parts at a time and thus mounts faster.

Our engineers select the correct pick up head to be used based on the shape and weight of the parts, and the machine follows these instructions automatically during the assembly process.After picking up a component the optical centring camera of the MY300 takes a picture of the part, whilst moving it towards the mounting area.

The Pick & Place then automatically identifies the leads of the part, the dimensions, the rotation and places the part on the correct position defined by the X and Y coordinates of the CAD program.The Pick & Place machine can also measure resistance, capacitance, and inductance of the component all “on-the-fly”.

These measurements make the process slightly slower, but increase the accuracy and avoids mistakes, a critical point when you produce prototype assemblies.

During the assembly process, the Pick & Place machine keeps different logs that we can analyse later.
These logs contain a huge range of information including mounting time, speed, pick errors, mount errors, head usage, we can even check kitting information and machine errors too. 

The Pick & Place machine also registers the program used for every order.The most common error is an identification error, when the machine fails to identify the component from underneath using its camera. We can improve the success rate with light settings or with reteaching the component to the machine.

Sometimes the parts get stuck in the feeders or tubes so that the machine cannot pick them up. In that case we need to manually remove the parts, and adjust the component feed for the machine to pick up again.

We also get errors when the correct pick-up head is not selected, or when fiducials are not detected. Our machine operators are there to solve these kind of errors.We have some parts which we cannot mount or require special care:

1.Minimum pitch: Components with a minimum pitch of 0.4 mm can be placed. For smaller pitches, we evaluate part by part for the mounting possibilities

2.Special components – special tools: Special components need special tools, such as LED’s with lenses, special connectors, edge connectors, MELF components,… For prototype production it can be more efficient to place such components by hand..

3.Minimum tape length – extra components needed: The tape width should be at least 8 mm and we need a minimum 50 mm to push the tape into the feeder. For tube and tray components we do not have these limitations. For smaller components up to 1212, we require at least 10 extra parts in the tape, for other components we require 1 extra component.

Sometimes, the Pick & Place machine rejects components, the reasons can be due to a number of factors including incorrect pick up, bad vacuum, excess placement head acceleration or failed identification.

The Pick & Place machine has a bin where it drops these parts which are presumed bad or not identified.Sometimes components drop while moving and get lost in the machine, from experience our engineers try to optimise the pick’n place programs to avoid such errors.


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