Electronics Manufacturing Education by UTechtic

The goal of this post is to introduce the electronic component placement step in an SMT process, and the automated pick-n-place equipment used to do so.

Objective 1: To be able to name the two steps that may precede the placement step.
Objective 2: To be able to choose the two layers of a PCB assembly that components are placed upon.
Objective 3: To be able to name the piece of automated equipment used for placement.
Objective 4: To be able to name the three common types of component packaging.

The first step in the SMT process, as we have defined it, is the stencil printing step. After that comes one of two steps. Either an inspection takes place, or the components are placed. Some SMT processes do not include the inspection step at this point. We’ll focus on the placement step in this post.

Stencil printing produces a PCB with paste deposited on its pads. That layered combination of PCB with paste atop is base input to the placement step. The other inputs to the placement step are the electronic components; such as resistors, capacitors, integrated circuits (ICs), diodes, transistors, and others. These electronic components are placed on top of the paste on the pads.

The different pieces of automated equipment that are used to place the components are collectively called pick-n-place machines. There are many different versions, and some of them may be called by other names. We’ll refer to all of them as pick-n-place machines.

Pick-n-place equipment have component holders often called magazines. Into these magazines are loaded components that are themselves in different types of carrier packaging. Spools, tubes, and trays are the most common component carriers.

Spools are circular and have two sides with a gap in between. Think of a spool of wire, only the spool is so small that only one wire wraps around it at a time. Instead of a wire, this spool has a long strip of tape. And embedded in that tape along its length are components which are evenly spaced. Components are picked from the top of the tape.

Tubes are just that though more rectangular and somewhat flat. They carry components along their length. These components abut each other, and all are oriented the same way. Components exit the tube from one end.

Trays are rectangular pieces of plastic which contain columns and rows of wells which hold components. The tops are open faced to allow for the picking of components.

Spools, tubes, and trays are all ways of feeding electronic components to the pick-n-place. Nozzles are used to pick and place the components. These nozzles descend upon the components and with the help of vacuum can pick each component. It then moves to the precise location on the PCB that has already been loaded into the machine. When the vacuum is relieved, the component is released for placement.

Objective1: To be able to recollect the three main components of an SMT-PCB assembly, and
write them down or type them in, within 90 seconds.
Objective2: To be able to choose two of the three main components that are used in stencil
printing, by selecting boxes in a multiple-choice question, within 45 seconds.
Objective3: To be able to verbally name the preformed part that directs the solder paste
onto a PCB, using your voice, within 20 seconds.

Let’s focus on the manufacture of surface mount - printed circuit board assemblies using
automated equipment. That is to say, SMT-PCB assemblies for which hand placement and
hand soldering are minimal.
Furthermore, we make the distinction between the equipment and its pieces that are used
to produce the assembly, and the components that are present within the final assembly.
There are three main components that are present in a finished SMT-PCB assembly. These
are the PCB itself, the paste used for soldering, and various electronic parts. Variations and
extensions of these three basic components certainly abound; for our purpose of explanation
we’ll maintain these three. Each of the three are supplied by other manufacturers.

Depositing solder paste to the finished pads on a PCB surface is the first major step of
addition in the assembly manufacturing process. And it must be done in defined locations on
the PCB with specified thickness of the solder paste.
To accomplish this there must be some setup prior to the step, which can include material
selection, loading of material, equipment programming, and inspections of configurations
before, also product after, the step. Setup, inspection, and the value-added step are
considered together as a unit operation.
There are two predominant methods of applying solder paste to a PCB. The first, and most
widely used, is a stencil and squeegee combination; in much the same way that logos are
printed onto T-shirts. Another method is to dispense solder paste from a nozzle in small
amounts at high speed. We choose to use the stencil and squeegee method for our
description. In this method, the stencil is a preformed part that determines where paste is
deposited onto the PCB.
To summarize, there are three main components present in a finished SMT-PCB assembly.
Two of those components are used in the primary stencil printing step. In addition to those
two components, a preformed stencil is required for this step.

Fishbone diagram for Stencil Printing