SelectIF 2040

Name: SelectIF 2040
Brand: Interflux Electronics
SKU: SelectIF-2040

Selective soldering flux

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.
Jet fluxing or microjet fluxing or drop jet fluxing is a technology used in electronics assembly to selectively apply flux to the surfaces to be soldered in the selective soldering process and sometimes also in the wave soldering process. The flux is needed to deoxydise these surfaces. A nozzle shoots tiny drops of flux from a pressurised flux tank to the bottom side of a PCB board. The nozzle can be positioned in an X/Y plane (spot fluxing) or can be moving along a path in the X/Y plane (line fluxing). Usually the PCB is standing still during flux application but some stand alone systems like ICSF Select can apply the flux while the board is moving which can be important in a high volume wave soldering process. The volume of flux can be programmed and depending on the system is expressed in drops/s, Hz,... For spot fluxing the time can be programmed and for line fluxing the speed can be programmed. The goal of the jet fluxer is to apply flux to the surfaces to be soldered which are the surface of the pin of the component and the surface of the trough hole of the PCB. Depending on the size of component and the pin to hole ratio there are several ways to program the fluxer so that the flux will end up on the surfaces to be soldered. This requires some experience. It is also recommendable that no flux will be applied outside the area of contact with soldering nozzle in the soldering process. This flux will see no soldering heat and will be left on the board as an unconsumed flux residue. Depending on the used flux and the sensitivity of the electronic unit, these residues can be critical for the reliability of the electronic unit. In this matter it is important to use a flux from the 'L0' classification that additionnally is absolutely halogen free. Fluxes that are specifically designed for selective soldering like SelectIF 2040 and IF 2005C give the best chance to apply the flux only on the surfaces to be soldered in combination with the best soldering performance. Furthermore it is important that the positioning of the jet fluxer is calibrated on a regular basis to make sure that the nozzle is exactly there where it has been programmed to be. When there is doubt if the jet fluxer is depositing the flux where it is programmed to be deposited, a PCB board can be fluxed without the following preheating and soldering step. When the board exits the machine it can be inspected from the bottom side to verify the correct flux application. A problem that is is sometimes witnessed is blocking of the nozzle by dried up flux residues. Some systems verify if the flux is coming out of the nozzle but others not. In this matter it is advisable to use fluxes from the 'OR' classification, meaning that they do not contain rosin nor resin which are sticky substances that can cause this nozzle blocking. Also a regular cleaning of the nozzle is advisable. If a flux filter is present in the system, check that filter for obstruction on a regular basis. Do not increase flux tank pressure to solve a nozzle blocking problem.

Key advantages

Water based soldering fluxes are liquid fluxes that have water (H2O) as their principal solvent. 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. However, 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. There is a good chance that this will increase the acceptance of water based fluxes on the market. Also the global ecological awareness has improved substantially lately which drives a lot of companies towards a more ecological and sustainable policy. This will also translate into a better acceptance of water based fluxes on the market.
A large process window in time and temperature is usually needed when soldering components and PCBs (Printed Circuit Boards) with heavy thermal mass. These boards and components require a lot of heat to get them to soldering temperatures. This takes time and in some soldering process also requires elevated temperatures. The soldering chemistry will have to withstand/survive these increased times and elevated temperaures. The biggest challenge is soldering heavy thermal mass through hole components on a heavy thermal mass PCB. On a through hole the required heat for soldering is needed on both sides of the board. This heat is usually applied only from one side and will have to pass through the board to the other side. If the PCB board has many Cu-layers, thick Cu-layers, and layers that are fully connected to the through hole barrel, a lot of heat will be deviated to the side and more heat will have to be applied to the board to get enough heat on the other side. In some processes the heat is applied from both sides of the board in a preheating. This will facilitate trough hole soldering on these thermally heavy electronic units. However if there are temperature sensitive components present on the side where the preheating is applied, care must be taken not to overheat and (pre)damage those components
High temperature resistant
Residues after soldering are inherent to the soldering process. Some soldering products will leave more residues than others. In general low residue soldering products have the preference. Residues are usually undesirable for more potential reasons. One of those reasons is esthetical. When the end customer receives his boards, obviously he likes them to be as clean as possible. Residues can also interfere with electrical pin testing, like ICT (In Circuit Testing) or flying probe. They might create contact problems and false readings that can obstruct production flow. Residues can also assemble on the test pins where they need to be cleaned off. These test pins are pretty fragile and the risk on damaging them during cleaning is real. Residues of the soldering process might also interfere with high frequency signals of sensitive electronic applications. Residues created by rosin and resin usually have poor compatibility with conformal coatings. Furthermore they are known to cause contact problems when they end up on connector contacts, (carbon) contacts of remote controls, contact surfaces of switches, relays, contactors,...and cause field failures. When the soldering product is classified as 'No-clean' it is an indication that the residues of these soldering products can remain on the electronic unit. This is based on passing reliability tests like Surface Insulation Resistance (SIR) tests and electro (chemical) migration tests. There are many standards worldwide that specify such tests. The most accepted standard is the IPC standard. In these reliability tests a test board with a comb pattern is soldered with specified parameters with the soldering product. The test board is submitted to high humidity and elevated temperature conditions over a defined period of time during which the surface insulation resistance is monitored. This surface insulation resistance cannot drop below a defined value and boards are also visually inspected with a microscope for anomalies like e.g. electro (chemical) migration.
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.
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.
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.
VOC stands for Volatile Organic Compound. In general VOCs are considered non environment friendly. Some countries or regions restrict the emissions of VOCs by legislation. Alcohols are VOCs. In some cases, the use of alcohol based soldering fluxes in the wave soldering process of an electronics manufacturing can give a problem with the VOC emission restrictions. A simple solution in such a case is to use a VOC-free soldering flux. In general this is a water based flux. Beside the elimination of VOC-emmissions, water based fluxes have more advantages to alcohol based fluxes, like lower consumption, no fire hazard, no need for special transport and storage, lower smell in the production area,...However, water based fluxes in general are more sensitive to the correct spray fluxer settings to get a good flux application on the surface and in the through holes. In some cases they also might require a bit more preheating to get the water evaporated.
In 2006 legislation restricted the use of lead (Pb) in electronics manufacturing. However there were a lot of exemptions formulated, mainly due to the lack of long time reliablity experience with the lead-free alloys. This resulted in a lot of electronics manufacturing sites that were using both lead-free and Pb containing alloys in their soldering processes. For wave and selective soldering, a lot of electronic manufacturers desired the use of the same flux chemistry with both types of soldering alloys. This was because they were familiar with the chemistry in terms of reliability. Also introducing new materials in a manufacturing can require a lot of paper work, extra storage capacity, etc...Although the lead-free alloys require higher operating temperatures than the Pb-containing alloys, by increasing the applied flux quantity in a lot of cases the same flux chemistry can be used for both alloys. However in some cases, usually when soldering electronic units with high thermal mass, it is not possible to use the same flux for both soldering alloys. In these cases, usually a flux with higher solid content is needed. A lot of solder wires and solder pastes are available with the same flux for both lead-free and SnPb-alloys.
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.