|Ask the Experts|
October 12, 2011
Components Jumping Out During Wave Soldering
We recently started having a sporadic problem. When components reach the wave solder pot, the components jump out of their holes. The problem doesn't appear to be caused by vibration, and the wave machine fingers have been checked. Any ideas of what might cause this?
|Expert Panel Responses|
It is not uncommon for through-hole parts to rise up out of their holes when coming into contact with the molten wave of solder in a wave solder machine or selective solder machine. There are a number of reasons for this, but the main (root cause) reason is simply oxidized component leads that resist wetting in the molten solder. If solderability is poor, the leads resist immersion into the molten solder, and if the resistance is high enough, even components that have a fairly large body mass will simply "float" up out of the plated-through holes due to the lack of wetting tension from the solder. This can happen on components that have a lead-free finish more so than a tin-lead or gold finish. The reason is that lead minimizes oxidation somewhat, and gold oxidizes very little. Lead-free finishes that consist of SAC305 or similar alloy (nearly all tin) on the component terminations can oxidize very quickly (read: shelf life of less than 1 year). The original RoHS requirements went into effect in 2006. It is now 5 years later. With the number of older through-hole components aging, the phenomena of components not wanting to wet is also increasing.This is not limited to through-hole parts, it is also true of SMT parts as well. There are other factors that can cause components to "float", but these are usually secondary causes. They include the aspect ratio of the hole diameter to lead diameter, mass or weight of the component body, lack of flux to promote good wetting (flux helps overcome the surface tension of the solder), and other causes. Keep in mind that SN100C solder has greater surface tension than 63/37, also. Some suggestions:
I suspect it is probably a combination of things. Until the solder wets the leads the component has a degree of intrinsic buoyance because of the density difference between the component and the solder. If the leads are slow to wet the this will tend to cause the components to rise up but it is unlikely that this would cause the component to "jump out". If there is thin air trapped under the component this will expand rapidly with the heat of the wave further lifting the component, this expansion can be rapid. The combination of the two effects slow lead wetting and rapid expansion of trapped air could conceivably cause a very light to "jump out".
Senior Applications Chemist
One possible problem could cause this: Leads are longer than past. Could be a set up problem with their insertion tool and the trim set up of the leads after placement. They should check their mechanical set up of the insertion system.
Global Segment Manager
Air Products & Chemicals, Inc.
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