OSPI 3311M

Flux for soldering OSP


Interflux® OSPI 3311M is an alcohol based no-clean flux for soldering OSP finished boards that have passed one or more reflow cycles. OSPI 3311M provides optimised through hole fill on degraded OSP finishes.

OSPI 3311M 10L angle


Interflux® OSPI 3311M is a no-clean flux that especially has been developed for high volume soldering of OSP-boards that have passed one or more reflow processes.

OSPI 3311M is an optimised version of OSPI 3311 for residue formation and odour.

Most OSP-finishings will degrade quickly after reflow, making (through hole) wetting in wave or selective soldering a challenge, especially with lead-free alloys.

The elements of OSPI 3311M have been carefully chosen to promote (through hole) wetting on these degraded OSPs, especially with high conveyor speeds and low preheat temperatures.

Moreover, the flux is absolutely halogen free and has been designed to be safe and reliable.

OSPI 3311M meets IPC requirements.

Suitable for

  • Wave soldering is a bulk soldering process used in electronics manufacturing to connect electronic components to a PCB board. The process is typically used for through hole components but can also be used for soldering of some SMD (Suface Mount Device) components that are glued with an SMT (Surface Mount Technology) adhesive to the bottom side of the PCB before passing through the wave soldering process. The wave soldering process comprises three main steps : Fluxing, preheating and soldering. A conveyor transports the PCBs through the machine. The PCBs can be mounted in a frame to avoid adjusting the conveyor width for every different PCB.  Fluxing is usually done by means of a spray fluxer but also foam fluxing and jet fluxing are possible. The liquid flux is applied from the bottomside of the PCB on the surface and in the trough holes. The purpose of the flux is to deoxydize the solderable surfaces of the PCB and components and allow the liquid soldering alloy to make an intermetallic connection with those surfaces resulting in a solder joint.   The preheating has three main functions. The solvent of the flux needs to be evaporated as it loses its function once its has been applied and it can lead to soldering defects like briding and solder balling when it contacts the solder wave in a liquid state. Water based fluxes in general need more preheating to evaporate than alcohol based fluxes. The second function of the preheating is to limit the thermal shock when the PCB contacts with the liquid solder of the solder wave. This can be important for some SMD components and PCB materials. The third function of the preheating is to promote through hole wetting of the solder. Because of the temperature difference between the PCB board and the liquid solder, the liquid solder will be cooled down when going up the through hole. Thermally heavy boards and components can draw away so much heat from the liquid solder that it is cooled down to the solidification point where it freezes before it gets to the top. This is a typical problem when using Sn(Ag)Cu alloys. A good preheating limits the temperature difference between PCB board and liquid solder and hence reduces the cool down of the liquid solder when going up the through hole. This gives a better chance that the  liquid solder will reach the top of the through hole.  In a third step the PCB board is passed over a solder wave. A bath filled with a soldering alloy is heated up to soldering temperature. This soldering temperature depends on the used soldering alloy. The liquid alloy is pumped through channels up into a wave former. There are several types of wave formers. A traditional setup is a chip wave combined with a laminar main wave. The chip wave jets solder in the direction of the PCB movement and allows to solder the back side of SMD components that are shielded of wave contact in the laminar wave by the body of the component itself is. The laminar main wave flows to the front but the adjustable back plate is positioned like this that the board will push the wave into a back flow. This will avoid the PCB being dragged through the reaction products of the soldering. A wave former that is gaining popularity is the Wörthmann-wave that combines the function of the chip wave and the main wave in one wave. This wave is more sensitive to the correct setting and bridging. Because of the fact that lead-free soldering alloys need high working temperatures and tend to oxydise quite strongly, a lot of wave soldering processes are done in a nitrogen atmosphere. A new market tendency and the considered by some as the future of soldering is the use of a low melting point alloy like e.g. LMPA-Q. LMPA-Q needs less temperature and reduces oxydation. It also has some cost related benefits like reduced electricity consumption, reduced wear ot of carriers and no need for nitrogen. It also reduces the thermal impact on electronic components and PCB materials.

  • OSP is an Organic Surface Protection used in PCB manufacturing to preserve the solderability of the PCB board during storage and in between the different soldering processes. It is the most economical surface protection. The main limitation is that a lot of OSPs will degrade after that they have seen a lead-free reflow profile. This can result in reduced through hole wetting of the through hole components in wave and selective soldering.The time between the reflow soldering process and the wave or selective soldering process is important in this matter. Some OSPs show signs of degradiation already 4 hours after  the lead-free reflow soldering process. Low melting point solder pastes need lower temperatures in the reflow soldering process and substiantially reduce the degradation of most OSPs.  A soldering flux that has been specifically designed to improve wetting on OSP surfaces that have seen a lead-free reflow profile, like OSPI 3311M can compensate for the degradation of the OSP coating and provide acceptable soldering results.

  • Selective soldering is a soldering technology in electronics manufacturing, typically used for PCB designs with mainly SMD (Surface Mount Device) components for reflow soldering and only a few through hole components that cannot pass through the reflow soldering process. These are usually thermally heavy mass components like e.g. big transfo's or thermally sensitive components like e.g. film capacitors, displays,  connectors with sensitive plastic bodies, relays, etc... The selective soldering process allows to solder these through hole components without protecting or affecting the SMD components on the bottom side of the PCB.  The selective soldering process is very flexible as the parameters can be programmed for each solder joint separately. The main limitation of the process however is the throughput or the production capacity. This can be considerately improved when using a low melting point alloy that allows for faster soldering speeds increasing production capacity up to 100% (double). The process starts with the application of a liquid flux that will deoxydize the surfaces to be soldered. This flux is applied by a micro jet or drop jet fluxer that shoots little drops. The correct calibration and programming of this fluxer is essential to get good soldering results. A common mistake is that flux is applied outside of the contact area of the soldering nozzle. This flux will remain as an unconsumed flux residue. For some fluxes and sensitive electronic circuits this can lead to increased leakage currents and failure in the field. It is advisable to use fluxes that are specifically designed for selective soldering and that are absolutely halogen free. The IPC classification for fluxes allows up to 500ppm of halogens for the lowest activitiona class but also these 500ppm can be critical, so absolutely halogen free is the key word. The next step in the process is preheating. This process step evaporates the solvents of the flux and provides heat to support good through hole wetting of the solder. Soldering is a thermal process and a certain amount of heat is needed to make a solder joint. This heat is needed from the bottom as well as from the top of the through hole component to be soldered. This heat can be provided by the preheating and by the liquid soldering alloy. Some basic machines do not have preheating, they will have to apply all heat through the liquid soldering alloy and in general they use higher temperatures for soldering. A preheating unit is usually a short wave IR (infrared) unit that applies the heat from the bottom side of the PCB. In most cases, the time and power of the preheating can be programmed. For thermally heavy boards and applications, top side preheatings exist. Usually they are hot air (convection) units where the teperature of the air can be programmed. When using this unit, it is important to know if there are any temperature sensitive components on the top side of the board that might be affected by this preheating.  Several systems for soldering exist. The one where the PCB board is standing still and only the soldering nozzle is moving is definitely preferred as all G-forces should be avoided when the solder solidifies. In the soldering step, a liquid soldering alloy is pumped through a soldering nozzle.There are different nozzle sizes and shapes available, wide nozzles, small nozzles, long nozzles and short nozzles.  Depending on the components to be soldered, one is preferred to another. In general wider nozzles and shorter nozzles give better heat transfer and are preferred. Smaller and longer nozzles can be used for situations with limited accessibility. Wettable nozzless are preferred to non wettable nozzles as they give a much more uniform flowing of the solder and more stable soldering results. Nitrogen flooding of the nozzle is advisable to have a stable flowing of the solder. The nitrogen is preferrably preheated because when not, it will cool down the solder and the PCB. The optimisation of the soldering program is essential for optimisation of the throughput/capacity of the selective soldering machine. This will focus on finding the minimal times and maximal speeds that give good through hole wetting in combination with no bridging.

Key advantages

  • For OSP surface finishes

  • Colophony, also called rosin, is a substance derived from trees that is typically used in soldering fluxes. It can be used in liquid fluxes as well as in gel fluxes. Colophony containing fluxes can be identified by the denomination 'RO' in the IPC classification. Colophony in general provides a good process window in time and temperature but has a number of disadvantages depending on the application that the colophony containing flux is used in. In liquid fluxes for wave and selective soldering, the colophony will give an increased risk on blocking the nozzle of spray and micro jet flux application systems, resulting in more maintenance and higher risk on bad soldering results. The residues of a rosin (=colophony) based flux in the soldering machine and on tools and carriers are quite hard to remove and a solvent based cleaner is usually needed. When the flux with colophony accidentally ends up on the contacts of a connector or contact comb structures like for a remote control or in electro mechanical contactors / relays / switches, it is known to give contact problems and malfunctioning of the electronic unit in the field.  Furthermore the residues of the flux that remain on the board can give contact problems with electrical pin testing ( ICT= In Circuit Testing) which can result in delays in production because of false errors. This usually requires cleaning of the PCB and/or the test pins. These expensive test pins are rather fragile and sensitive to be damaged by cleaning.  Furthermore the residues of a rosin flux are known not to be compatible with conformal coatings in time. The rosin residue forms a separation layer between the PCB and conformal coating that in time can cause detaching of the conformal coating and also cracking, especially when the electonic unit experiences a lot of temperature cycles (warming up and cooling down).  For those reasons fluxes without colophony and more specifically fluxes from the 'OR' classification are generally used for wave and selective soldering. Colophony can also be used in solder wires. Although the colophony provides a good process window in time and temperature, it is very sensitive to discoloration when heated. The discoloration will depend on the type of colophony and the temperature it has seen. As soldering tip temperatures are usually quite high, the colophony in the solder wire will give quite heavy visual residue formation around the solder joints. This will distinguish them from the other solder joints made in reflow, wave and selective soldering. When this is not desirable a cleaning operation needs to be performed. Furthermore the fumes of a colophony containing solder wire are considered hazardous. A fume extraction is mandatory but anyway advisable for any hand soldering operation. Colophony containg wires are still being used quite a lot but colophony free solder wires and more specifically solder wires from the 'RE' classification are gaining importance. Colophony is also used in solder pastes. Beside giving a good process window in time and temperature, it also provides a good stability of the solder paste on the stencil. This will facilitate a stable printing process and hence stable soldering results and defect rates. The discoloration of the rosin in reflow soldering is not so prominent as it is with a solder wire because the temperatures in reflow soldering are lower than in hand soldering. Still the rosin residue has poor compatibility with conformal coating and in time after thermal cycles it might show cracks or detatching of the conformal coating. Although most manufacturers will apply the conformal coating over the solder paste residues, for optimal results it is advisable to clean off the solder paste residues. Giving the benefits of colophony described above, most solder pastes contain colophony.

  • Absolutely halogen free soldering chemistry contains no intentionally added halogens nor halides. The IPC classification allows up to 500ppm of halogens for the lowest 'L0' classification. Soldering fluxes, solder pastes and solder wires from this class are often referred to as 'halogen free'. Absolutely halogen free soldering chemistry goes one step further and does not contain this 'allowed' level of halogens. Specifically in combination with lead-free soldering alloys and on sensitive electronic applications, these low levels of halogens have been reported to cause reliability problems like e.g. too high leakage currents.  Halogens are elements from the periodic table like Cl, Br, F and I. They have the physical property that they like to react. This is very interesting from the point of view of soldering chemistry because it is intended to clean off oxides from the surfaces to be soldered. And indeed halogens perform that job very well, even hard to clean surfaces like brass, Zn, Ni,...or heavily oxidized surfaces or degraded I-Sn and OSP (Organic Surface Protection) can be soldered with the aid of halogenated fluxes. Halogens provide a great process window in solderability. The problem however is that the residues and reaction products of halogenated fluxes can be problematic for electronic circuits. They usually have high hygroscopicity and high water solubility and give an increased risk on electro migration and high leakage currents. This means a high risk on malfunctioning of the electronic circuit. Specifically with lead-free soldering alloys there are more reports that even the smallest levels of halogens can be problematic for sensitive electronic applications. Sensitive electronic applications are typically high resistance circuits, measuring circuits, high frequency circuits, sensors,...That's why the tendency is to move away from halogens in soldering chemistry in electronics manufacturing. In general when the solderability of the surfaces to be soldered from component and PCB (Printed Circuit Board) are normal, there is no need for these halogens. Smartly designed absolutely halogen free soldering products will provide a large enough process window to clean the surfaces and get a good soldering result and this in combination with high reliability residues. 

  • The wetting ability of a soldering product refers to how well the activation of the soldering product is able to clean off oxides from the surfaces to be soldered. These oxides need to be removed to enable the liquid soldering alloy to penetrate the surfaces to be soldered. When the quality of the surfaces to be soldered in electronics manufacturing is normal, it is possible to use a soldering product from the lowest activation class L0. In general, only when surfaces are degraded or when the base metal is hard to solder, then a product with a higher activity or increased wetting ability is used. Such surfaces can be for example chemical Sn that was applied too thin or stored too long before soldering, components or PCB boards that were stored too long in hot and humid conditions and are heaviliy oxidised, non protected Ni, brass,... Another possible reason for using a product with increase wetting ability is ease-of-use. For example a solder wire with increased wetting ability in general will provide faster soldering and is not so sensitive to the correct handling required to produce a good hand soldered solder joint. In high volume hand soldering operations for electronc units that have not so high requirements to the residues after soldering, solder wires with increase wetting ability are often used. Also for robot soldering and laser soldering solder wires with increase wetting ability are often used because in general they have better properties for these processes.

  • The wetting speed of a soldering alloy is how fast that soldering alloy is able to penetrate the surfaces it is meant to solder. This speed is determined by the alloy itself, by how the heat is applied, by how fast the activation is able to deoxydise the surfaces or surface finishes to be soldered and by the type of surface or surface finish itself. In some soldering processes the wetting speed can be very important. For example hand soldering processes where electronic components are manually soldered to the PCB boards and robot soldering processes often require high wetting speeds to reduce process times and increase throughput. For those processes chosing the correct solder wire can give a substantial advantage. The soldering alloy and the surfaces to be soldered in most cases are determined by the electronics design engineer and cannot be chosen freely. The way that the heat is applied to the surfaces to be soldered is determined by the design of the machine or chosen soldering station, but the correct settings of the temperature(s), contact surfaces of the heating element and timing of solder wire feed are important to optimise wetting speed. However, the choice of  the flux inside of the solder wire often is the parameter that makes the difference in wetting speed. The correct type of flux as well as the correct flux quantity inside of the solder wire in this matter can be different for every process. Often this will require some trial and error but there are some general rules. In terms of flux quantity inside of the wire: this in most cases is related to the thermal mass of the parts to be soldered. Higher thermal mass will require higher flux quantities. For example, soldering a through hole solder joint  in general requires a higher flux content than soldering a SMD solder joint. There are many types of fluxes. In general, higher activated solder wires give faster wetting speeds but this is not always true. When the type of activation is not optimal for the surface to be soldered, more activation will not result in a faster wetting speed. The classification of the solder wire gives an indication of the activation. The most popular and accepted classification for solder wires and soldering products in general is the IPC. L0 is the lowest activation class and the standard, it should be suitable for all normal quality conventional surfaces used in electronics assembly. L1 is the lowest activation class but with a halogen content up to 0,5%. These halogens will in most cases give a faster wetting speed. The next activation classes are M0 and M1. M stands for Medium activation. 0 again stands for up to 500ppm of halogens and 1 in this case stands for up to 2% of halogens. It has to be noted that an M0 classified solder wire will not necessarily give higher wetting speeds than an L1 classified solder wire, it can also be the other way around.  The next activation classes are H0 and H1.  H stands for High activation. 0 again stands for up to 500ppm of halogens and 1 in this case stands for more than 2% of halogens. Also here an H0 classified solder wire will not necessiraly give higher wetting speeds than an M1 classified solder wire, it can also be the other way around. Soldering products of the H class are to be treated with care as they can be corrosive and need to be cleaned off, preferrably in a automatised cleaning process. For soldering electronic applications without cleaning after soldering, in general only products from the L0, L1 and M0 class are being used.

  • A brushable residue left by a soldering product can be moved with a dry brush without the aid of a solvent. Most residues of soldering products can only be moved by dissolving them with a suitable solvent or cleaning liquid. The advantage of a brushable residue is that the cleaning operation is much quicker and easier. This quality is very much appreciated in visual control and rework and repair after the soldering process in electronics manufacturing.

  • A conformal coating is a protection layer often used on electronics devices that are submitted to harsh atmospheres. In most cases the conformal coating is applied on the electronic unit without previous cleaning. Some residues of the soldering process and the soldering products can have a negative effect on the long term adhesion of the protection layer on the electronic unit. This will usually result in small cracks where atmospheric moisture can penetrate and condensate, potentially resulting in increased leakage currents or (chemical) electro migration. However some soldering products have a high compatability with conformal coatings. Soldering products that leave little residues and are classified as 'OR' usually have a high compatibility with conformal coatings.

  • Alcohol based soldering fluxes are liquid fluxes  that have alcohol(s) as their principal solvent(s). The majority of liquid fluxes used in electronics manufacturing are still alcohol based. The main reasons are their historical use and hence market share and their in general larger process window compared to water based fluxes. Water based fluxes have numerous advantages to alcohol based fluxes, like lower consumption, no VOC (Volatile Organic Compound)-emmissions, no fire hazard, no need for special transport and storage, lower smell in the production area,...However a lot of electronic manufacturers seem to prefer the larger process window of alcohol based fluxes to the advantages of water based fluxes. Alcohol based fluxes in general are less sensitive to the correct spray fluxer settings to get a good flux application on the surface and in the through holes. Furthermore they are more easily evaporated in the preheating and give less risk on remaining solvent drops creating solder balls, solder splashes or bridging upon wave contact. Another parameter that is complicating the implementation of water based fluxes is that changing a flux in some cases can be a time consuming and costly process. It usually involves homologation testing and approval of end customers. Specifically for EMS (Electronic Manufacturing Servivces = subcontractors) this can be a challenge. Some countries have already implemented legislation that limits the VOC-emission of factory chimneys or imposes taxes on VOC emissions. This appears to be an extra incentive to change to water based fluxes. A recent development forced a lot of manufacturers to look into water based fluxes. The COVID-pandemia in the beginning of 2020, suddenly increased the demand for alcohol based desinfectants to that extent that at a certain moment the availability of alcohols on the market was pretty much non existing. Luckily the industry that produces alcohols was able to ramp up their volumes just in time to avoid electronic manufacturers to fall without fluxes to operate their soldering machines.

  • When a soldering product is labelled No-clean, this means that  soldering product has passed reliability testing like a Surface Insulation Resistance(SIR) test or an electro(chemical) migration test. These tests are designed to test the hygroscopic properties of the residues of the soldering product under elevated temperature and high relative moisture conditions. No-clean is an indication that the residues can remain on the electronic unit after the soldering process without being cleaned. This will apply for by far most of the electronic applications. For very sensitive electronic applications, which are typically high resistance electronic circuits, high frequency electronic circuits, etc... it is possible that cleaning of the electronic unit is necessary. It is always the responsibility of the electronic manufacturer to judge wether cleaning is necessary or not.

  • RoHS stands for Restriction of Hazard Substances. It is a European directive: Directive 2002/95/EC. It restricts the use of some substances that are considered Substances of Very High Concern (SHVC) in electrical and electronic equipment for the territory of the European Union. A listing of these substances can be found below: Please note that this info is subject to change. Always check the website of the European Union for most recent information: https://ec.europa.eu/environment/topics/waste-and-recycling/rohs-directive_nl https://eur-lex.europa.eu/legal-content/EN/TXT/?uri=CELEX:32011L0065 1. Cadmium and cadmium compounds  2. Lead and lead compounds  3. Mercury and mercury compounds(Hg)  4. Hexavalent chromium compounds(Cr)  5. Polychlorinated biphenyls (PCB)  6. Polychlorinated naphthalenes (PCN)  7. Chlorinated paraffins (CP)  8. Other chlorinated organic compounds  9. Polybrominated biphenyls (PBB)  10. Polybrominated diphenylethers (PBDE) 11. Other brominated organic compounds  12. Organic tin compounds (Tributyl tin compounds, Triphenyl tin compounds)  13. Asbestos  14. Azo compounds  15. Formaldehyde  16. Polyvinyl chloride (PVC) and PVC blends  17. Decabrominated diphenyl ester (from 1/7/08)  18. PFOS : EU directive 76/769/EEC (not allowed in a concentration equal to or higher than 0.0005% by mass) 19. Bis(2-ethylhexyl) phthalate (DEHP)  20. Butyl benzyl phthalate (BBP)  21. Dibutyl phthalate (DBP)  22. Diisobutyl phthalate 23. Deca brominated diphenyl ester (in electrical and electronic equipment) Other countries outside of the European Union have introduced their own RoHS legislation, which is to a great extent very similar to the European RoHS. 

Physical & chemical properties

Clear colourless liquid
Solid content
5.3% +/- 0.5%
Halide content
Density at 20°C
0.825 g/ml ±0.01
Acid number
42 mg KOH/g ±5
Trade name
OSPI 3311M No-Clean Soldering Flux
Available packaging
  • 1L HDPE bottle
  • 10L HDPE drum
  • 25L HDPE drum
  • 200L HDPE barrel
  • custom packaging on request

Quality compliance


OSPI 3311M complies with the European Standard EN 61190-1-1(2002) which outlines the requirements for soldering fluxes for high-quality interconnections in electronics assembly.


OSPI 3311M complies with the European Union's RoHS directive for restricting the use of certain hazardous substances in electrical and electronic equipment.

ISO 9001

OSPI 3311M is produced at Interflux Electronics in Belgium, which has been certified year after year with the ISO 9001 standard for reliable quality management systems.

Test results

Property Result Method


Flux designator



Qualitative copper mirror


J-STD-004A IPC-TM-650 2.3.32

Qualitative halide - Silver chromate (Cl, Br)


J-STD-004A IPC-TM-650 2.3.33D

Qualitative halide - Spot test (F)


J-STD-004A IPC-TM-650

Quantitative halide


J-STD-004A IPC-TM-650 2.3.35C




SIR test


J-STD-004A IPC-TM-650

How to use OSPI 3311M

Through hole filling

OSP finished boards can benefit with enough flux, lower preheat temperatures and high solder pressure on the (first) wave to get good through hole filling.

Applying the flux

Spray fluxing: It is advised to use a double spray stroke during fluxing, whenever possible and to keep the flux air pressure low. The nozzle traverse speed is set to a value which ensures that every point on the board is sprayed twice, (once from each side). Resulting in a 50% overlap on the spray pattern. This will give the most uniform spray pattern coverage. Spray pattern coverage can be checked by passing a piece of cardboard through the spray fluxer. Remove it before the preheat unit. Additionally the spray fluxer settings need to be checked by passing a glass plate or empty circuit board through the fluxer. Remove it from the machine before it reaches the pre heater unit and check it on flux quantity. There may be no drops present. Drops are a sign of excessive flux and are difficult to evaporate. Reduce the flux amount until defects typical for a too low flux amount like, webbing, flagging, shorts and icicles are observed. From this point increase the flux level again until defects disappear.


The flux has been designed to perform well on low preheating settings. The recommended preheat temperature measured on the topside of the boards is 80°C-100°C (176°-212°F) . Higher preheating is possible for electronic units with high thermal mass. More preheating can promote through hole wetting on these units but beware not to exhaust the flux. The flux itself has no lower limit for the preheating but the solvent should be evaporated before wave contact.

Preheat slope: 1-3°C/s

Wave contact

Typical wave contact or dwell time value is 3-4s when using a single solder wave. For double wave soldering systems typical values are 1-2s for the first wave and 2-4s for the second wave. Lower total dwell time limit is 2s. Solder wetting can be optimal at lower contact times however longer contact times facilitate total flux wash off from the boards. The maximum upper limit will be determined by flux exhaustion and physical limitations of the board and components. Indications for flux exhaustion are bridging, icicling, webbing, ...


Store the flux in the original packaging, tightly sealed at a preferred temperature of +5° to +25°C


OSPI 3311M is flammable. Please always consult the safety datasheet of the product.