Pick and Place Machines

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SMT Quick-Tips: Selecting a Pick and Place Machine

How do you select a pick and place machine?  A Pick and Place machine is the second step in a paste, place, reflow assembly operation. The “Place” function follows the “solder paste” function (stencil printer). The ‘place’ operation selects and delivers a component over the board and drops it into position. The simplest form of pick and place operation is by hand, that is, manually picking a component from a bin and, with the aid of a pair of tweezers and a magnifying glass, positioning it on the board and completing the operation with a hand-held soldering iron.

This method works well if you are only doing occasional boards. Other things to consider – the size of the components (big or small) – affect the time required to hand place and solder. Fine pitch components are another issue, where more precision and accuracy are required, and the human factor comes into play. The work then become more tedious and time consuming.

First, we will focus on machine-assisted manual systems for users interested in going from a couple boards a day to much higher production volumes. Fully automatic systems are complex enough that we’ll cover them separately.

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PRODUCTION VOLUME

Let’s start by addressing production ranges for various types of machine-assisted manual systems. For purposes of comparison, since all circuit boards vary in size and complexity, we’ll talk about volumes in terms of components per hour, or CPH. This will help you to decide what level of automation you’ll need.

On the very low side of the scale – using a manual hand system – the only expense is the appropriate hand tools for non-machine assisted manual placement. At the high end of the spectrum, these machines are often modular or customized for high speed unattended operation. Buyers in this market are likely looking more at ROI than initial cost.

Manual and semi-automatic systems

Fig 1:Example of manual head and armrest for support

A manual pick and place system is desirable for small, growing operations that need to increase their hand-held production volumes incrementally while also improving quality, thus reducing rework or rejects; however, the accuracy of placement is still limited by the capability of the operator. Benefits of a machine-assisted manual system include:

    Less operator fatigue
    Fewer placement errors
    Better control
    Improved yield, less rework

A machine-assisted manual system can be equipped with features such as an X-Y indexing table with vacuum pickup head or pen; ergonomic fixturing to help relieve operator fatigue; and additional fixturing for θ (rotation) and Z (height) positioning in addition to X and Y.

Fig 2: Component trays and feeders

Some machines offer an optional liquid solder paste dispenser, which is applied just before placing the component on the board if a stencil printer has not been used. Additional options include:

    Component Handling Trays
    Liquid Dispenser
    Tape Feeders
    Feeder Racks
    Vision Assist option
    Optional Stands

In most cases, machine assisted manual systems can be purchased with just the bare necessities, and desirable options can be added later as they’re needed.

Fig 3: A vision-assisted manual machine

Semi-automatic systems

Today there are very few semiautomatic machines still being made because of the increasing affordability of some of the more automated systems on the market. They were originally introduced at a time when the leap from manual to fully automatic systems was just too cost prohibitive and were made available with some features to assist the manual operation.

More correctly referred to as “enhanced manual” systems, semi-automatic pick and place machines typically include a computer interface with a vision system that shows where the components go, but the placement itself is still done manually. This type of machine helps the operator position ultra-fine pitch components more accurately for low-volume applications, an operation that is very difficult to accomplish using a simple machine-assisted manual machine.

Ease of use

Most pick and place machines will handle a fairly wide variety of board sizes, with a work table designed to accommodate boards up to 16” x 24”. There is also ease of control over the components, which aids in accuracy, along with a simple learning curve. In most cases, no training is required.

Don’t overlook electrical requirements. Make sure the machine you buy will plug-and-play in your environment without pulling in new wiring or else plan on an adapter/transformer.

AUTOMATIC PICK AND PLACE MACHINES

We will start by talking about two aspects of machine capability – accuracy and repeatability, and Pick and Place centering methods.

ACCURACY AND REPEATABILITY

For production machines, we typically recommend looking for a machine with accuracy of +/- .001” and down to fine pitch capability of 12 mil on a repeated basis. Less expensive machines often don’t meet this spec, so that’s something to be aware of.

Most low-cost machines will also not come standard with a computer or software which could help with the repeatability aspects if not the accuracy. While some may offer enhanced technology – most do not.

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