The recent European directives and legislations by nations around the world have mandated elimination of lead usage in some sectors of the electronics industry by 2006. 

Reflow Process Considerations
The reflow process window for conventional soldering is relatively wide. The melting point of the eutectic solder is 183°C. The lower temperature limit for reflow is usually 200°C. The upper limit is around 240°C, which is the maximum temperature that most components can be exposed.

These high and low temperature limits provide a process window of over 40°C. The lead-free alloy used for BGA solder balls has a melting point of 217°C.  This alloy requires a minimum reflow temperature of 235°C to ensure good wetting. The maximum reflow temperature is in the 245°C-260°C, depending on the package size. This narrows the process window for lead-free soldering to 10-25°C.

Vapor Phase Reflow
Vapor Phase Reflow Soldering (VPS), is a method of reflow technology developed by ATT Labs in NJ back in the early 80’s.   The process was widely used in the 80’s.  In the early 2000’s there was a massive relocation of commodity board manufacturing offshore.  Remaining SMT producers re-tooled to produce higher value added and smaller run boards.

When it comes to reflow for either eutectic or lead free, the absolutely best method is Vapor Phase Reflow Soldering.

The principle of vapor phase or condensation reflow soldering involves immersing a populated PWB into a saturated vapor, which has been created by boiling a liquid with a specific boiling point.

In the case of lead-free alloys, which generally have melting points of 217°C or 221°C, fluid used would typically have a boiling point of 230-240°C.  For Eutectics the boiling fluid is 215°, or the industry standard, 3M’s Fluorinert® FC-70.

The heat of the PCB and components, when immersed in the vapor, can never exceed the boiling point of the liquid; this completely eliminates any risk of overheating. Any fluid residue on the PCB evaporates and the PCB cools prior to exiting the machine.

Heat transfer to the PCB is accomplished almost irrespective of the shape, color and thermal mass involved. For example, it is possible to solder such disparate items as a 0.5 mm thick PCB and an 18-layer board simultaneously. Both will get sufficient heat for soldering but neither will overheat.

Using VPS reflow, the physically defined and unchangeable heat transfer of the condensing vapor means that there are no variations in the process as long as the thermal mass remains the same. This ensures consistent repeatability and reproducibility; the only requirement is the presence of vapor.

Further the atmosphere in a VPS reflow machine is oxygen free.  Therefore there are fewer oxides and less persistent soils remaining on the board when extracted which greatly reduces the cleaning load.

R&D Technical Services machines are being used everyday in a wide variety of markets such as, but not limited to: SMT Solder Reflows, Lead Free Soldering, Curing, Drying, Mechanical Attachment and Plastic Package Testing.

Vapor Phase is the leader in Safe, Repeatable Heat Transfer with such advantages as:

1. Uniform Temperatures
2. Fast Even Heat Transfer Regardless of Product Size or Mass
3. Minimum Liquids Times
4. Absolute Limits to Maximum Temperatures
5. Low Oxygen Environment 
6. Highly Repeatable
7. Easy to Use
8. Short Setup Time

Why AMS Materials?
AMS Materials has been working with vapor phase soldering since the 80’s.  All the features and benefits of VPS have always been true but are critical when one is considering lead free.  We work with 3M, R&D Technical Services and Branson Ultrasonics, which are also pioneers in the industry.

When it comes to re-work, R&D recently introduced its new Vapor Phase Reflow re-work station.  In the short time since its introduction it is already an Industry recognized revolutionary process and patented.  Replacing classic hot air re-work stations, we have successfully pulled a 1.5KG (3.3lb) 1500 pin connector off a surface mount backplane.  By the way, that same connector can only be attached using VPS reflow.  Ask us how.

Selecting the right process, the proper fluid and the subsequent best cleaning process can be challenging and frustrating.  We have navigated these waters before and with tremendous success.