Ask the Experts
January 25, 2022 - Updated
April 20, 2016 - Originally Posted

Solder Splashing During Wave Soldering

We are experiencing solder splash during wave soldering while using both adjustable and dedicated pallets resulting in the splash on the boards creating ICT failures.

The solder splash is popping up from the solder flow. What is the likely reason for this?


Expert Panel Responses

Have you confirmed the preheat profile is meeting the flux suppliers recommendations?

If using a VOC free flux, it is critical to ensure that the board is "dry" prior to it coming into contact with the wave otherwise the wet flux can cause spitting that could result in the issues you are seeing.

Gerard O'Brien
S T and S Testing and Analysis
Gerald O'Brien is Chairman of ANSI J-STD 003, and Co Chairman of IPC 4-14 Surface Finish Plating Committee. He is a key member of ANSI J-STD 002 and 311 G Committees Expert in Surface finish, Solderability issues and Failure analysis in the PWA, PWB and component fields.

From the information given, two potential causes need to be ruled out.
  1. If there is residual liquid flux (alcohol or water based), rapid exposure to solder pot temperatures will cause a rapid phase change from liquid to vapor, possibly causing a splash.

    Reducing the amount of flux sprayed onto the board, or increasing the pre-heat to drive off the flux's solvent would eliminate this cause.
  2. If the pallets are too cood when passing through the wave, there could be a splash. Reducing the conveyor speed or increasing pre-heat settings (or both) could help. If hole fill suffers, or icycles begin to form, you may have gone too far with this remedy.

Mitch Holtzer
Director of Reclaim Business
Alpha Assembly Solutions
I've been in the soldering materials/applications industry for 25 years. Since joining Alpha, Ive been the global product manager for preforms, wave soldering flux, solder paste and more recently the Director of the soldering materials reclaim business.

There are a couple of issues to look at regarding the solder splashing up onto the bottom side of the board during the wave soldering process.
  1. Most wave solder equipment today have an inclined conveyor which is preset, so make sure this has not been changed.
  2. Check the amount of solder in the solder pot. If the solder level is too low, the solder being pushed off the back side of the solder wave as the board traverses across the wave, has a long way to go before getting back into the solder pot and this creates a rough flow of solder which will create solder splashes which can come back up and splash on the board.
  3. Dedicated pallets are typically thick which displaces the molten solder from the height of the wave, which create excess solder to splash into the solder pot which splashes back up onto the board.
With the fixtures, make sure the openings are smooth and at a low angle to allow the solder to flow to the area to be soldered. Don't run the board to deep in the wave or as describe in 2 and 3 above this will enhance to solder to splash up onto the board.

Hope this helps and if more is needed please let me know.

Leo Lambert
Vice President, Technical Director
EPTAC Corporation
At EPTAC Corporation, Mr. Lambert oversees content of course offerings, IPC Certification programs and provides customers with expert consultation in electronics manufacturing, including RoHS/WEEE and lead free issues. Leo is also the IPC General Chairman for the Assembly/Joining Process Committee.

Solder splashes during waver soldering are often caused by the application of excessive flux, and/or inadequate preheat. The volatile materials used in fluxes, typically solvents, will explosively vaporize upon contact with the solder wave. This causes solder splashes. If too much flux is applied then the preheat will not be able to drive off all of the volatile materials. If the preheat temperatures are too low or the dwell time too short, then again some volatile materials will be left on the circuit boards.

We recommend that the flux application rate be set to meet the manufacturers specifications. The pre-heat settings should also be set to meet the flux manufacturers specifications. In this case the amount of applied flux should be reduced, or the pre-heat time or temperature increased.

Tony Lentz
Field Applications
FCT Assembly
Tony has worked in the electronics industry since 1994. He worked as a process engineer at a circuit board manufacturer for 5 years. Since 1999, Tony has worked for FCT Companies as a laboratory manager, facility manager, and most recently a field application engineer. He has extensive experience doing research and development, quality control, and technical service with products used to manufacture and assemble printed circuit boards. He holds B.S. and M.B.S. degrees in Chemistry.

Without further information it's hard to say but could be flux left on the PCB while going through the wave especially if sizzling occurs or the Pump Pressures could be too high forcing solder through the vias and holes too strongly causing splashing on top side.

Greg York
Technical Sales Manager
BLT Circuit Services Ltd
Greg York has over thirty two years of service in Electronics industry. York has installed over 600 Lead Free Lines in Europe with Solder and flux systems as well as Technical Support on SMT lines and trouble shooting.

Your questions does not outline if the splash places solder on the top or the bottom of the assembly.

Regardless, under most circumstances this is caused by some type of turbulence in the wave area. If the solder is being splashed onto the top of the assembly, I would look at the waves as they transition from either stand-by mode to run mode or from off mode to run mode. Standby would be used with a system that has a tracking system that activates the waves. Make sure that when the flush of solder leaves the wave hardware area and returns to the solder pot you don't see excessive splashing upwards.

If splashing solder on to the bottom of the assembly, I would confirm it's a splash and not exhausted flux that has been over heated or over exposed to the wave dwell which is often confused as a splash as the solder will stick to the mask. If you can confirm it is a splash, look at the solder level in the pot and make sure you are at the right solder level.

John Norton
Eastern Manager
Vitronics Soltec
John Norton started his soldering career in 1983 for Hollis Engineering. He has also worked with Electrovert as a technical training manager and Vitronics Soltec for the last ten years. He has held various technical development and sales positions.

Potentially insufficient preheat not drying the flux before the wave. More common with a VOC-Free flux.

If not the flux, then possibly another source of moisture.
  1. Check the board temp entering the wave and adjust as necessary to be in line with recommendations.

    If not solved
  2. Try baking a board before soldering to drive out moisture.

Kay Parker
Technical Support Engineer
Indium Corporation
Kay Parker is a Technical Support Engineer based at Indium Corporation's headquarters in Clinton, N.Y. In this role she provides guidance and recommendations to customers related to process steps, equipment, techniques, and materials. She is also responsible for servicing the company's existing accounts and retaining new business.

This is going to be a large work volume project. I would recommend to check the following:
  • Wave profile settings: speed, temperature, wave height in combination with environment conditions (humidity, temperature)
  • Components and bare PCB state: moisture content, oxidation present, etc
  • Flux application: profile - frequency, area covered, volume - using a glass pallet is recommended and with the same device check the solder pot leveling
  • Using pallets is great but you will need to consider their mass/volume and compensate with the temperature settings and/or speed - lack of heat on the board can also cause issues

Georgian Simion
Engineering and Operations Management
Independent Consultant
Georgian Simion is an independent consultant with 20+ years in electronics manufacturing engineering and operations.
Contact me at
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