One evening when there were no good games on TV I let my girlfriend talk me into going to see a play. It was written by some famous guy and I reluctantly went. The part that stayed with me was when a young guy, the star, was asking himself, “To be or not to be…” Apparently, he was undecided about taking action and was wondering what would happen after he did.
This prompted me to consider if I could be a better PCB designer if I knew more about what happens after I finish my design and send it off to be manufactured. Ultimately, I found that with more knowledge about how my PCB comes to fruition into the world, from ghostly-design to full-fledged board, I would be able to design more around potential manufacturing and assembly challenges, specifically in my soldering choices.
PCB Manufacturing Processes
PCB manufacturing consists of two major processes: fabrication and assembly. Each process consists of several important steps:
PCB Fabrication Steps:
- The board image is created by laser or on a film.
- If there are multiple layers, inner layer etching is performed to uncover the copper traces.
- The layers are stacked and bonded together.
- The vias and mounting holes are drilled.
- Outer layers are etched.
- Where needed, holes are plated to provide conductive paths for current between layers.
- Solder mask is applied to protect surfaces and isolate traces.
- The silkscreen is printed, which is usually identification data, symbols or text.
- A metallic finish is applied to protect the board.
PCB Assembly Steps:
- An initial solder layer is put down on the board.
- Surface Mount Devices (SMDs) are placed on the board if included.
- To secure SMDs, solder reflow is performed where the solder is heated to form connections.
- Connections are inspected and, if necessary, rework, and manual securing are done.
- Through-hole components are mounted if included.
- To secure through-hole components, wave soldering is performed.
- Another inspection is done and another soldering stage may be applied, is necessary to ensure that all connections are secure.
- The boards are washed to remove any excess debris and for protection.
- For multiple PCB production, which is the most common, the boards are separated into individual units.
The result of the fabrication process is a PCB with traces, pads, and imagery ready for the parts to be installed. The fundamental method of installing or attaching the parts to the board is soldering. PCB manufacturers basically use reflow for SMDs, wave soldering for through-hole components or both for large-scale board assembly. The method or methods that are more applicable depend on the PCB design. By looking at wave soldering advantages and disadvantages we can determine whether it is better to wave or not to wave.
Knowing when to use wave soldering will get you a thumbs-up, for sure.
What are the Advantages of Wave Soldering?
Wave soldering has been around a long time and was the primary method of soldering components to PCBs when boards were larger, parts were practically all through-hole components and they were sparsely placed on the board. Wave soldering provided an automated way to produce large numbers of boards quickly.
Today, most PCB designs are focused on minimizing space, which reduces the separation between components and makes the use of SMDs and vias more attractive. These design attributes do not support the use of full board wave soldering and the added cost of its usage cannot be balanced against its speed.
Selective soldering, which is a type of wave soldering that targets specific components or regions of the board, is the solution for smaller boards with congested or mixed (through-hole and SMD) components. This wave soldering process has distinct advantages over full board wave soldering; including:
- No glue is needed to secure components during reflow soldering.
- Board areas where no soldering is required do not have to be masked off.
- Selective solder machines are generally cheaper to operate.
- Parameters for each are variable and can be more finely controlled.
- Allows wave soldering to be applied to boards with SMDs and vias.
What Are The Disadvantages of Wave Soldering?
When compared to selective soldering, full board wave soldering has disadvantages; including:
While comparisons and attributes can be difficult to understand, it is important to know the strengths of different processes.
The use of surface mount devices (SMDs) and multiple layer boards has increased the utilization of reflow soldering. If your board is comprised of only SMDs, reflow is the preferred soldering method. However, if your PCB design includes through-hole components as well, or exclusively, then some form of wave soldering will most likely be employed. The number of components, their spacing on the board and the size of your PCB run are all factors that will influence which wave soldering process is used. All of these are determined by your design.
As with all PCB design, good design for manufacturing (DFM) should be applied. This includes component type (through-hole or SMD) selection and spacing on the board. The use of a unified PCB design software package, such as Altium designer, PDNA provides you with all the tools you need to design your boards and answer the question to wave or not to wave.
For more information about wave or other soldering methods and how to design your PCB for them, contact an Altium PCB design expert.
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