There have been many new advancements in equipment for the lead free process for both wavesoldering and reflow soldering.

Wavesoldering:

Since the alloy used for lead free soldering has a higher liquidus temperature and does not wet as well at low temperatures, like lead solder does, many new advancements have been made in wavesoldering equipment.

One of the most unique and important advancement has been the enclosed nitrogen atmosphere system. This is a wavesolder that uses pneumatic flap gates at the entrance end (after the spray fluxer) and at the exit end of the wavesolder (after the solder bath), to maintain an inert preheat and soldering atmosphere (050ppm @ 27³m/h) so that the solder bath temperature can remain at 250c, while providing quality wetting and solder joints. This is very important because it allows for good wetting below 255c which is a critical temperature. If a system does not have the enclosed inert atmosphere then the solder bath temperature must be increased to at least 255c and higher or the conveyor speed must be reduced by 10% to 33%, to produce good wetting and solder joints. This increase in temperature not only affects the PCB and components but leaches the copper from component leads and the PCB. The amount of copper that is leached on a high production line can cause the need to replace 50kg of alloy every 4 days and requires the constant monitoring of the solder alloy to ensure that the alloy contains less than 1% copper. This is a very costly problem that can occur with older systems that do not have this option. If the solder temperature is maintained below 255c and the conveyor speed in decreased then production throughput is reduced and thermal damage can occur to both the PCB and the components caused by the increased dwell time in the solder bath. The enclosed nitrogen wavesolder addresses the thermal problems that can occur with lead free wavesoldering by creating an inert atmosphere for both the preheat and the solder bath which reduces the oxygen so that oxidization does not occur which increases wetting and the quality of solder joints. This allows the current profiles developed for lead solder to be used for lead free wavesoldering without changing processes and eliminates the need to test all components for higher thermal processes.

Reflow:

There have been many advances in reflow soldering to ensure a reliable and repeatable process and vapor phase reflow systems are leading the way.

Vapor phase reflow was one of the original reflow processes during SMT's infancy, many years ahead of convection, but it's popularity soon changed when the chemicals used were declared harmful and fluid cost sky rocketed.

Today though, vapor phase reflow is regaining its popularity and has made huge advancements in both the chemical fluids used and thermal profiling. The fluids used today are completely safe (used as lubrication for syringes in the medical industry) and are used in many areas of electronics, such as: leak detection, liquid to liquid thermal shock, final test, etc. The fluids used today are Galden, a liquid Teflon based material and have boiling points that range from 155c to 260c and the operational cost are about 20% less than a convection oven with nitrogen. The vapor created with the Galden is also 100% inert which is ideal for lead free and the heat transfer rate is approximately 10x that of convection with a near 0? across the board.

This brings us to thermal profiling capabilities of vapor phase. The new systems can now have patented processes in which the PCB stops at different levels with in the vapor where the density is different. The less dense the vapor is the slower the heat transfer rate. So when a board is profiled in the vapor phase it is done by the amount of time it spends at each vapor level. This allows vapor phase systems to achieve any profile desired from tent to plateau from curing to reflowing.

Vapor phase has always been a better reflow choice when it came to expensive boards, high mass and complex assemblies, because the assemblies get even heat quickly with out the possibility of over heating. Now with the safe lower cost fluids and the advancements in thermal profiling, vapor phase is becoming more and more common place in normal production.

The advantage that vapor phase brings to lead free soldering is it's ability to reflow at lower temperatures (224c for 217c alloy) and it's ability to run both lead and lead free in the same profile.

Do I have to change my current process or board design to solder with lead free?

In most cases yes you will have to change your current process and quite possibly your current board design, unless you are using an advanced wavesoldering system with closed nitrogen atmosphere or a vapor phase reflow system. Most soldering systems in the field are ill equipped to solder current assemblies with lead free solder, even if they are so called lead free systems, with out going to higher temperatures that can damage current assemblies and their components. It is not just the fact that lead free becomes liquidus at a higher temperature, but that it has poor wetting properties at lower temperatures and when your system does not address the wetting issue, then you must increase the temperature that your assembly reaches. Then you will need to be very careful and spend a lot of time to find profiles that reach a compromise between good wetting and safe assembly temperatures. If after testing you are unable to solder your assembly with out thermal damage then you will most likely need to change your board design for components made from materials that can handle the higher temperatures.