Flux Pen
Several Interflux® fluxes are available in a flux pen. The refillable flux pen has a very fine glass fibre tip that allows flux application only on the solder joint which avoids flux residue in the surrounding area giving esthetically clean soldering results. The non refillable flux pen is more economic.
Standard fluxes that are available in the flux pen: IF 8001, IF 6000, TerrIFic RP 65, IF 2005M, IF 2005C.
Suitable for
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Rework and repair on an electronic unit can be performed on defective electronic units that return from the field but can also be necessary in an electronic production environment to correct defects in the assembly and soldering processes. Typical rework and repair actions involve the removal of solder bridging, adding of solder to poor through hole filled components or adding missing solder, replacing wrong components, replacing components that are placed in the wrong direction, replacing components that have defects related to the high soldering temperatures in the processes, adding components that were left out of the process due to e.g. availability or temperature sensitivity. The identification of these defects can be done by visual inspection, by AOI (Automated Optical Inspection), by ICT (In Circuit Testing, electrical testing) or by CAT (Computer Aided Testing, functional testing). A lot of repair operations can be done with a hand soldering station that has a (de)soldering iron with temperature setting. Solder is added by means of a solder wire that is available in several alloys and diameters and contains a flux inside. In some cases a liquid repair flux and/or a gel flux are used to make the hand soldering process easier. For bigger componnets, like BGAs (Ball Grid Array), LGA's (Land Grid Array) QFNs (Quad Flat No Leads), QFPs (Quad Flat Package), PLCCs( Plastic Leaded Chip Carrier),...a repair unit can be used that simulates a reflow profile. These repair units are available in different sizes and with different options. In most cases they contan a preheating from the bottom side that is usually IR (Infrared). This preheating can be controlled by a thermocouple that is placed on the PCB. Some units have a pick and place unit that facilitates the correct positioning of the component on the PCB. The heating unit is usually hot air or IR or a combination of these two. With the aid of thermocouples on the PCB, the heater is controlled to create the desired soldering profile. In some cases the challenge is to bring the component to soldering temperatures without remelting adjacent components. This can be difficult when the component to be repaired is big and has small components near to it. For BGAs with balls made of a soldering alloy, a gel flux can be used or a liquid flux with higher solid content. In this case the solder for the solder joint is provided by the balls. But also the use of a solder paste is possible. The solder paste can be printed on the leads of the component or on the PCB. This requires a different stencil for each different component. The BGA can also be dipped in a special dipping solder paste that first is printed in a layer with a stencil with one large aperture and a certain thickness. For QFNs, LGAs QFNs, QFPs, PLCCs,...solder needs to be added to make a solder joint. In some cases QFPs can be hand soldered but the technique requires experience so the use of a rework unit is preferred. QFPs and PLCCs have leads and can be used with a dipping solder paste. QFNs, LGA's QFNs who do not have leads but flat contacts cannot be used with a dipping solder paste dipped because their bodies would contact the solder paste. In this case the solder paste needs to be printed on the contacts or on teh PCB. In general it is easier to print solder paste on the component than on the PCB, especially when a so-called 3D stencil is used that has a cavity where the position of the component is fixed. Replacing through hole components can be done with a hand (de)soldering station. This is usually done by placing a hollow desoldering tip over the bottomside of the component lead that can suck away solder from the hole. The desoldering tip will have to heat all the solder in the through hole until it is fully liquid. For thermally heavy boards this can be very difficult. In this case, also the top side of the solder joint can be heated with a soldering iron. Alternatively the board can be preheated over a preheating before the desoldering operation. Soldering the through hole component is usually done with a solder wire that contains more flux or alternatively extra rework flux is added to the through hole and/or on the component lead. For larger through hole connectors, a dip soldering bath can be used to remove the connector. If accessibilty on the PCB is limited a nozzle with its size adapted to the connector can be used. The use of flux in this operation is recommended.
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Hand soldering is a technology in electronics manufacturing that uses a hand (de)soldering iron to make a solder joint or to desolder a component from a PCB board. The process is mostly used in rework and repair but also to solder single components that have been left out of the bulk soldering process (reflow or wave soldering). This can be due to the availability or the temperature sensitivity of these components. The soldering iron usually is part of a soldering station that has a power supply that controls the temperature of the soldering iron. This temperature can be set according to the used soldering alloy and usually is between 320°C-390°C. The soldering iron has an exchangeable soldering tip that can be chosen according to the component to be soldered. For optimal heat transfer the biggest possible soldering tip is recommendable, certainly when soldering (heavy thermal mass) through hole components. For soldering thermally heavy components and boards, the power of the soldering station is also important to keep the set temperature of the soldering tip. In rework and repair, changing the soldering tip for every different component is not realistic and only a few soldering tips are used. Soldering tips exist to solder several surface mount solder joints in a row like for e.g. SOICs (Small Outline Integrated Circuit) and QFPs (Quad Flat Package). To promote heat transfer and flowing of the solder, the soldering tips are wettable, meaning that they make an interaction with the soldering alloy. During soldering these tips will oxidize and they can loose their wettability which will obstruct heat transfer. This can be avoided by cleaning the soldering tip with e.g. a tip tinner. After some time the soldering tips will also wear out and will need to be replaced. The life time of the soldering tip can be optimised by avoiding the use of abrasive or agressive soldering tip cleaners or by avoiding mechanically cleaning the soldering tip with e.g. steel wool or sand paper. The use of an absolutely halogen free tip tinner is advisable. In hand soldering, the solder for the solder joint is usually provided by a solder wire. A solder wire is available in several diameters and several alloys, and has a certain quantity of a certain type of flux inside. The alloy is usually the same or a similar alloy as the bulk soldering process (reflow, wave or selective soldering). The diameter is chosen according to the size of the solder joint. The flux content in the solder wire is usually determined by the thermal mass of the component and board to be soldered. (Heavy thermal mass) through hole solder joints need more flux. More flux content will also give more visual flux residue after soldering. Sometimes extra flux is needed which in most cases is a liquid rework and repair flux but also can be a gel flux. The type of flux/ solder wire is determined by the solderability of the surfaces to be soldered. With normal solderability of electronic components and PCB boards an absolutely halogen free 'L0' type of flux/solder wire is advisable. In general a hand soldering operation is performed like this: Set the temperature of the soldering tip according to the used soldering alloy. For lead-free alloys, the advised working temperature is between 320°C and 390°C. For more dense metals like Nickel, the temperature may be elevated to 420°C. The use of a good soldering station is important. Use a soldering station with a short response time and with enough power for your application. Choose the correct soldering tip: to reduce the thermal resistance, it is important to create a large as possible contact area with the surfaces to be soldered. Heat up both the surfaces simultaneously. Slightly touch with the solder wire, the point where soldering tip and the surfaces to be soldered meet (the small quantity of solder ensures a drastic lowering of the thermal resistance). Add subsequently without interruption, the correct amount of solder close to the soldering tip without touching the tip. This will reduce the risk on flux spitting and premature flux consumption!
Key advantages
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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.
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Fast and easy application
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High repeatability