Reflow Oven Horizontal ConvectionTM Defined
Leading up to the development of lead-free soldering alloys, Horizontal Convection* was developed for the reflow process. Getting the correct reflow temperature profile, with the narrow process window in lead-free applications, is now more important than ever. In each chamber or zone, air is circulated toward one side of the reflow oven above the PCB and toward the opposite side of the reflow oven below the printed circuit board (PCB), forming a cyclone around the PCB. The forced air circulation results in a uniform temperature profile along the entire circuit board assembly. This technology is ideal for the precise reflow profiles for lead-free soldering.
*Patent # 6,936,793
Horizontal Convection Defined
1. The main difference between Horizontal Convection
and traditional reflow oven technology.
In traditional reflow ovens, air currents introduced are
vertically from above and below the PCB. In Horizontal Convection, air is circulated horizontally in one direction across the top of the board and in the opposite direction beneath the board. This is key. This prevents hot spots and this parallel "angle of attack" enhances the ability of the air streamto infiltrate the spaces underneath component bodies such as BGAs and J-leaded devices.
2. Lower overall equipment cost and operation cost.
Because the Horizontal Convection system requires neither plenum now air reintroduction apparatuses, it is (due to its simplicity) more reliable and less costly. There is no need for costly flux management systems, as there is no sticky flux residue in the oven, greatly reducing the need for constantcleaning, maintenance, and servicing.
3. Eliminates hot spots across the board.
Temperature uniformity is ensured by controlling the air flow around the PCB and by having consistent temperature, air pressure, air velocity, volume, and direction across the board. The top and bottom of the board receive the air from the outsides toward the center, which acts to counter the center hot spot/cool-outside condition. This minimizes thermal stress to PCB materials and components.
4. No flux management system needed.
There is no flux residue because the air is recirculated within the confines of each reflow chamber. Chambers each contain all the elements needed to be self-sufficient: heating elements, fan blades, inert gas suffusers and exhaust ports. The air never comes in contact with cooler surfaces and thus does not condense anywhere in the reflow oven.
5. Uses less nitrogen in inert atmosphere applications.
An advantageous side effect of the Horizontal Convection system is an ability to produce low oxygen ppm (parts per million) levels when purging the inert gas, because the volume of space affected includes only the confines of each reflow chamber. By contrast, in traditional reflow oven design the chamber, as well as the upper and lower plenums must be purged.
6. The best profiles...Period!
There are multiple reasons for this claim. Heated air within each reflow zone is completely controllable and precise. Temperatures across the PCB are uniform with no hot spots because air is circulated horizontally in a circular or"cyclone" motion around the PCB. Temperatures across the entire PCB, front to back, are virtually identical. DDM Novastar is willing to compare its superior profiles to any other profiles in the industry.
Cross-section of a GF-120 reflow oven with
Horizontal Convection. Air is recirculated
within the confines of each chamber.
Reflow profile taken in a GF-120HC, 3 zone reflow oven. Actual board temperatures
recorded with 6 thermocouples evenly
positioned across the board.