Interflux® Purgel is a neutral cleaner/conditioner for pumps and valves of dispensing systems that cleans and preserves dispensing system parts when not in use.
Solder paste jetting is a contactless technology used in electronics assembly to apply solder paste to the PCB board. The technology is more flexible than stencil printing because it allows the presence of components on the side of the PCB where the solder paste is being applied. However it is a slower process than stencil printing. A nozzle jets with high speed small deposits of solder paste to the solderable pads of the SMD (Surface Mount Device) components. The challenge of solder paste jetting is repeatability and stability of the process. A big parameter in this matter is the solder paste. The form stability of the solder paste and the volumetric stability of the deposits in time are important. In many cases the machine manufacturer will test the jetting ability of the solder paste and approve the solder paste for its machine and/or define parameters for optimal usage.
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.
Dispensing is a technology used in electronics manufacturing to apply solder paste (or an adhesive) from a syringe to a PCB (Printed Circuit Board). Dispensing is a more flexible way to apply solder paste than standard stencil printing because it allows to selectively apply solder paste with the presence of pre-assembled components on the surface. However dispensing is a much slower process than stencil printing and not suitable for high volume productions. That's why it is mostly used to add extra solder paste in an SMT (Surface Mount Technology) assembly line but also for rework and repair and in prototyping. Dispensing can be done manually or automatically. In rework and repair this is usually done manually with a system that applies pressurised air to the plunger of the syringe and the solder paste is pushed out through a needle. But it can also be done by hand with a manual plunger. In automated processes like in a stand alone dispenser in a SMT assembly line or a in a dispenser built in a stencil printer there are two main systems to push the solder paste out of the syringe: Air pressure and the Archimes screw. Air pressure systems are usually cheaper but the volumetric stability of the solder paste deposits is a bit more difficult to control, especially when the syringe is almost empty and there is a bigger volume of compressed air in combination of less material in the syringe that needs to be moved by this air pressure. Systems with the Archimedes screw are usually more stable and faster. However depending on the solder paste quality, they can be sensitive to some very fine particles of the solder paste that are squashed between the Archimedes screw and the side walls which can block the needle where the solder paste comes out. The smaller and longer the needle, the higher the risk on needle blocking. The needle size is chosen according to the size of the desired solder deposit. The grain size of the solder paste is chosen according to this needle size. In general a type 3 solder paste can be used for needles with an inner diameter bigger than 0,5mm, a type 4 for needles with an inner diameter down to 0,25mm, a type5 for needles with an inner diameter down to 0,15mm. The dispensing performance of a solder paste can vary from one type to another in terms of volumetric stability and sensitivity to needle blocking. If a syringe of solder paste has been stored too long, too warm or too cold, this can also affect the dispensing performance. How much time and temperature will affect the dispensing performance may also vary from one solder paste to another. Solder paste for dispensing can be available in different types of syringes required by the machine where its intended use is for. They can also be available with different types of plungers required by the viscosity of the solder paste to be dispensed. Standard sizes for syringes are 5CC, 10CC and 30CC.
Helps preserves dispensing system parts when not in use
MYDATA MY 500 is a popular solder paste jetter. When the jetter is idle or not functional the solder paste inside of the jetting system can dry out. It needs to be purged and preferrably replaced with a product that does not dry out and does not interfere with the materials of the jetting system. Purgel has specifically been designed for this purpose.
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