If you’re soldering Printed Circuit Boards (PCB), you will most likely be using an SMT reflow oven. Reflow ovens are used to heat the PCB and the solder paste to a specific temperature. This allows the solder paste to reflow and create a permanent bond between the components and the board.
One of the most important decisions to make when choosing a reflow oven is how many heating zones it should have. In general, the more zones a reflow oven has, the more consistent and precise the heating process will be. This can result in higher quality solder joints and fewer mistakes or defects.
A typical SMT reflow operation requires three main phases: the preheat phase –to bring the PCB to soak temperature; the soak stage – to activate the flux; and then the reflow stage - where the oven reaches peak temperature.
How Many Zones Should Your Reflow Oven Have?
The question remains: how many zones should your reflow oven have?
The answer depends on a few factors, including the size and complexity of your PCBs, the types of components you are soldering, and your desired level of precision.
In general, smaller PCBs with simpler component layouts can get by with fewer heating zones, while larger, more complex boards with densely packed components may require more zones to achieve consistent heating across the entire board.
In high-volume manufacturing, the longer 8 to 10 zone ovens might work best. However, with low or medium volume, shorter reflow ovens with 4 to 6 zones could work with tin/lead and simple lead-free designs.
Below are some other factors to consider when choosing your reflow oven:
1. Solder Paste Alloy Used - Tin/Lead or Lead Free
The solder paste peak reflow temperature can be instrumental in making your decision. Most paste manufacturers will have a technical data sheet and give you a general range of heating time for the different stages of the reflow cycle.
2. The heated length of the reflow oven
The heated length of the reflow oven needs to be determined. The heated length is different from the oven’s total length. The heated length can be found in the manufacturer's specification.
3. Number of Reflow Boards Per Minute
The number of reflow boards per minute is generally how many soldered assemblies are leaving the oven in approximately 20 seconds. There really are minor variations between ovens but this is something to consider as well.
4. Type of Heat
There are a few choices of heating methods that are typically performed within an oven.
Other heating methods typically performed within a chamber (oven) but that rely on different heating methods include:
Convection
Convection heating is the most often used method to reflow circuit boards. The boards and their assembled components are passed through heated, circulating air either horizontally or vertically to surround the boards and entire assembly with evenly distributed heat. Every zone in a reflow oven retains its own heat as the boards pass through.
Infrared heating
Infrared heating is not typically used with boards in smaller or medium volume productions. It is used most often in specific applications where the heating temperature needs to increase quickly with very little soaking time. The boards are passed through a direct IR heat source. It isn’t the right fit for an assembly with different board sizes and heating profiles.
There are many things to take into consideration when deciding the best reflow oven for your needs. However, if you need to process complex PCB assemblies with heavy ground planes in lead-free, then profiling will best be achieved with an 8 to 10 zone reflow oven.
