Friday, March 1, 2024

Selecting Assembled PCB Desktop Manufacturing Equipment

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This buyers’ guide explains how desktop manufacturing equipment can be used for full product realisation and to understand how production considerations inevitably impact the design process. When designing a product the most important factor is defining a product’s success. However, with advancements in desktop manufacturing, most parts can now be produced in-house, which saves a lot of time.

Presented in this article are the different technologies and buying tips for the most popular types of desktop manufacturing equipment. For a new product, the first thing is the product realisation process, which encompasses the entire cycle of production and mechanical design so that all components including assembled printed circuit boards (PCBs), are designed to fit into the mechanical design.

Then, if everything is okay, PCB designs are verified and finalised and their Gerber files are sent for production of the PCBs to the PCB manufacturer. Sometimes, manufacturers may revise these files before they proceed further. Also, they may provide turn-key solutions, where they make PCBs, source components, make stencils and assemble PCBs, all at one place to save time, in order to meet the pace of the market.

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Key factors involved in PCB manufacture

Basic equipment for PCB production on the basis of the board as input are the screen or stencil printer, pick-and-place machine, reflow oven, board DE-fluxing machine, stencil cleaning machine and automated optical inspection system. Steps involved in producing a PCB are:

1. The screen printer applies solder paste to the PCB on pad locations.
2. The pick-and-place machine picks up, inspects and puts surface-mount technology (SMT) components in a particular position on programmed locations.
3. Board DE-fluxing and stencil cleaning machines are used for cleaning the PCB and stencil, respectively.
4. Automated inspection equipment are used for inspection of the assembled PCBs for detection of any wrong placement or missing components.

Desktop stencil printer
Fig. 1: Desktop stencil printer

Electronics manufacturing using SMT is a method in which electronic components are assembled with automated machines that place components on the surface of a board. The process involves making the PCB and assembling the components on that PCB.

After checking availability of various types of desktop manufacturing equipment, you should consider the various types available and be familiar with the associated pros and cons. All PCB prototyping work can be done in-house and time-to-market can be reduced.

Selection criteria

Stencil printers. The first stage of automated assembling of PCBs is stencil printing. For this we require stencil, solder paste and printer. Components are either leaded or SMT soldered to the board and exposed areas of the board are tinned or plated with solder. Stencil printers are available in three configurations, as given below:

Manual. Simple printing devices are suitable where high-precision alignment of a stencil-PCB is not critical. These are suitable for low volumes of up to 150 boards per day.

Semi-automatic. Loading and unloading of PCBs is done manually in this case. These as suitable for professional electronics products with medium volumes of up to 500 boards per day.

Fully-automatic. These are used for precision and in-line high-volume production of more than 500 boards per day.

Nearly 85 per cent of the defects produced in an SMT production line result primarily from the printing process. Careful selection of the printer is therefore imperative. Major considerations for selection of stencil printers are explained below:

Maximum size. Maximum size of the PCB the printer can handle; length and breadth expressed in millimetres

Minimum size. Minimum size of the PCB the printer can handle; length and breadth expressed in millimetres

PCB thickness. Lower and higher limits of the PCB; specified in millimetres

Stencil size. Maximum and minimum size of the stencil; length and breadth specified in millimetres

Printing accuracy. Specified in millimetres and Sigma limits

Cycle time. Standard printing time under optimum condition specified in seconds

Printing mode. Single- or double-side printing

Cleaning system. Dry/wet/vacuum

Operation system. For the integral computer

Automated SMD pick-and-place machines. SMT component placement systems, commonly called pick-and-place machines, are used for placing surface-mount devices (SMDs) onto a PCB. These are also capable of placing of a broad range of electronic components like capacitors, resistors and integrated circuits onto the PCBs from tapes and trays at a high speed with a high degree of precision.

Benchtop model of pick-and-place machine
Fig. 2: Benchtop model of pick-and-place machine
Automatic desktop pick-and-place machine
Fig. 3: Automatic desktop pick-and-place machine

Benchtop pick-and-place models offer low-cost solutions for low- to medium-volume SMT placement applications. Selection of the machine is normally based on the following parameters:

Placement rate. Capacity of placing a number of components in one hour; specified as components per hour (CPH)

Placement accuracy. Accuracy of placing components at designated place on the PCB; specified in µm and Sigma limits

Component size. Dimensions of length and breadth specified in millimetres

Minimum. Minimum size of component that can be handled

Maximum. Maximum permissible size of components the machine can pick and place

Minimum component lead pitch. Distance between two adjacent leads; specified in millimetres

Range of components. Capability of placing a variety of components such as LEDs, ball-grid arrays, quad-flat packages and SMT connectors

Picking modes. Capability of picking parts from tapes, tubes or trays and loose components
Software. Windows-based, user-friendly



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