Should a Secondary Pot Be Used for the Wave or Another Wave System to Support Lead-free Production?
This is a question most people are reviewing now.
Buying a new wave system or a new lead-free pot depends on a few critical items: Will your lead-free production volume support a new system or just a secondary pot? Do you have the space to install a second system? Will it be standalone or inline?
How you proceed is based on your current and long-range ramp up in production volumes with lead-free.
Buying a new wave and dedicating it to lead-free will be easier than having a second pot and switching it out every time you go from lead-free to tin/lead and back again. Scheduling the switch is a concern as well as heat up time.
Once you get through the installation setup (power hook-up, exhaust, etc), the system will always be available for lead-free product runs. With automatic system startup, operators will not have to wait for the system to heat up, which can up to three hours depending on the size of the pot.
If using a secondary pot, caution must be maintained at all times to prevent lead contamination of the lead-free alloy.
Using one wave and two pots may be a good use of available floor space and resources. However, there are critical issue concerns: Process discipline and pot contamination.
When switching from a tin/lead pot to a lead-free pot, review the following guidelines:
• Everyone involved in the lead-free production must be trained in the differences of using lead-free alloys vs. tin/lead.
• Storage area for the lead-free bar alloy must be different than the tin/lead alloys.
• Mark each pot, one “Lead-free Only” and the other “Lead alloy.”
• Dross removal tools — have a dedicated set for lead-free and mark them as such or paint the tools green.
• When using lead-free in the wave area, remove all tin/lead bars from the area and hide them.
• One or two people should know where the tin/lead bars are stored.
• Specification sheets for the different alloys should be located at the wave systems.
• Have a sign on the wave system listing lead-free alloy in use and the flux.
• Place one lead-free solder bar on top of the wave. This can be used as a reference to the manufacturer’s alloy being used. Note: alloy manufacturers are starting to use a triangular shape for the individual bars to indicate it is a lead-free bar.
• Have only one operator responsible for re-supplying the alloy in the pot.
Pot contamination is a real concern. There is no such thing as overkill when trying to prevent contamination of the lead-free pot.
To prevent lead contamination of the lead-free pot, when swapping out the tin/lead pot take the following precautions: 1.) With the tin/lead pot removed, clean all of the board support fingers and make sure all of the lead is off. 2.) Clean out tin/lead splashes. When the pot is heating up, trapped air will expand and cause a spray or fountain of molten alloy. This spray can deposit alloy everywhere inside the wave. Operators have a tendency to remove the solidified alloys and return it to the pot. It only takes two pounds of lead to contaminate a 1,000-pound pot!
The cost to purge a contaminated pot (time and materials) is approx $18,000.00. An individual must remove the contaminated alloy, purge it twice with pure tin alloy and finally re-supply with new lead-free alloy. This alone will take two to three days. And this is only the beginning of your problems — the next step is locating the contaminated products that your company just shipped out!
There is no substitute for a fully trained operator(s). A separate system would greatly reduce the probability of contaminating your lead-free process.
Consider all your options when deciding to purchase a wave system or a second pot. The problems associated with a new wave are considerably less.
Remember, RoHS starts July 1, 2006.
Have I Overlooked Anything in the Transition to Lead-Free?
As lead-free alloy requirements arrive this summer (RoHS), many production managers and their staff are busy reviewing their reflow systems’ and wave systems’ capabilities to see if they can achieve the lead-free process temperatures. Hopefully, you did this six to 12 months ago.
Take a moment with your staff to review the question “Is my pick-and-place system accurate enough to place components (ICs, chips and BGA devices) in lead-free solder alloys?”
Tin/lead alloys are more forgiving than lead-free alloys. If a component was not placed correctly, when heated in the oven, the temperatures, tin/lead solder alloys and belt vibrations cause a self-aligning of the components.
Lead-free alloys will not allow the devices to self-correct or self-align. Again, is your pick-and-place system accurate enough to do its job? When is the last time you had the system’s maintenance performed? Or is it time to start looking for another pick-and-place system with the accuracy you need?
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