Paste-Place-Reflow Tutorial

APPLY SOLDER PASTE
PLACE COMPONENTS
SOLDER REFLOW PCBs

Electronics are an integral part of our daily lives. Everything from our smart phones to our cars includes electronic components. At the heart of these electronics is the printed circuit board, also known as a PCB.

A basic PCB consists of a sheet of insulating material with a layer of copper foil laminated, and then chemically etched to divide the copper into separate conducting lines. These lines act as a wire between the board’s substrate materials. These boards can have multiple copper layers, and insulating layers, and can be simple or complex, depending on their functions.

PCB vs PCBA

A PCB (Printed Circuit Board) is a board that electrically connects electronic components using conductive tracks (or traces), pads, and other features etched from copper foil laminated onto a non-conductive substrate. PCB’s can be single sided (one copper layer), double sided (two copper layers), or multi-layer (outer and inner layers).

A PCBA (Printed Circuit Board Assembly) is the board after all the components and parts have been soldered and installed on the PCB, so that the completed board can perform the electronic function it was designed for.

The PCB assembly process is a simple one, consisting of three key steps: Paste, Place, and Reflow.

With each step of the process, a board manufacturer has both manual and automated options from which to choose. To help you better understand the PCBA process from start to finish, here is a little more info on each step.

Step 1 – PASTE (Stencil Printers)
In the first step, solder paste must be accurately placed onto a PCB with the aid of a stencil printer, which deposits the paste into the pattern of the circuit. This is done using a ‘stencil’ or foil. The paste is then disbursed over the stencil with a squeegee. Stencil Printers can be manual or automatic, and designed with frame or ‘frameless construction.

For more information, read the article ‘Selecting a stencil Printer’

Paste-Place-Reflow Product Selection Guide

Step 2 – PLACE (Manual or Automated Pick & Place)
Next, the electronic components are picked and precisely placed onto the board using a manual or automatic pick and place machine. These may be picked from a tray, reel, strip, or feeders, depending on your machine choice. Your machine choice is usually determined by your production requirements and your budget.

While components can certainly be placed by hand, using tweezers, it’s not very efficient or accurate, if you have many boards to do – or your components are very small. (which many of them are)
Pick and place machines range from small benchtop units to free standing floor model.

For more information, read the article ‘Selecting a Pick & Place Machine’.

Step 3 – REFLOW (Reflow Oven)
Finally, the solder paste must be heated until it melts and forms strong and reliable joints between the components and the surface of the board. This is accomplished through the use of a reflow oven which heats the solder to the proper temperature and then cools it down to a solid again.

For more information, read the article ‘Selecting a Reflow Oven’.

SMD Technology

In some instances, a mixed technology board with both SMD (surface mount device) and through-hole components (components with leads that are placed through holes in the bare boards) will be required. To solder the through-hole components on a mixed technology board, a wave solder machine or selective solder machine may be required.

Surface-mount technology began to be widely used in the late 1980s. IBM first demonstrated the technology in 1960 in a small-scale computer and later applied it in the digital computer used to guide Nasa’s Saturn V rockets. Since then, SMT components became much smaller and component placement on both sides of a board is far more common, allowing much higher circuit densities.

As a result, surface-mounted devices are usually small and lightweight. Surface mounting lends itself well to a high degree of automation, reducing labor costs and increasing production rates. SMDs can be one-quarter to one-tenth the size and weight, and one-half to one-quarter the cost of equivalent through-hole parts.

Industries that utilize SMDs include telecommunications, aviation, consumer electronics, wireless, automotive and instrumentation.