1).Connection (Interconnect) : provide mechanical and electrical connection/disconnect, which consists of connecting plug and socket, connecting cable, bracket, chassis or other PCB to PCB; However, the actual connection to the plate must be through surface mount contact.
2).A Active electronic component (Active) : in analog or digital circuits, you can control the voltage and current by yourself to produce a gain or switching effect, that is, you can change your basic characteristics in response to the applied signal. (the simplest and most direct understanding is that it always has an external power source, hence the name active).
B passive electronics (Inactive) : provides a simple, repeatable response without changing its characteristics when an electrical signal is applied. (the simplest and most direct understanding is that it does not need and does not have additional power to work, so the name passive).
3).Odd-form: the geometry factor is Odd, but not necessarily unique. Therefore, it must be manually mounted, and the shell (in contrast to its basic function) has a non-standard shape such as many transformers, mixed circuit structures, fans, mechanical switch blocks, etc.
Usage of SMD adhesive:
1) simple introduction of SMD adhesive, also known as SMD adhesive, it is the red paste in the uniform distribution of harderer, pigment, solvent, and other adhesive, mainly used to fix components on the printed board, generally with the method of dot coating to distribute. Paste components into the oven or reflow welding machine heat hardening. It and so called solder paste is not the same, once the heat hardening, reheating will not melt, that is to say, the thermal hardening process of the adhesive is irreversible. The application effect of patch adhesive will be different due to the thermal triangulation condition, the connection is different. Use according to the production process to choose the adhesive.
2). Purpose and use case of patch:
As a result of the production process, the way of the adhesive and the required characteristics are not the same.
1). Purpose of the adhesive:
(1) wave soldering process to prevent components from falling off during wave soldering;
(2) reflow welding process to prevent the falling off of another component in reflow welding;
(3) prevent reflow welding process and pre-coating process of components displacement and vertical;
(4) make marked wave soldering, reflow soldering and pre-coating;
2). Process for the use of patch adhesive;
(1) in the use of wave soldering, components are fixed on the PCB in order to prevent components from falling off when the PCB passes through the solder slot.
(2) in the double-side reflow welding process, in order to prevent the large components on the welded side from falling off due to the hot fusion of the solder, to make the SMT adhesive.
(3) used in reflow welding process and pre-coating process to prevent the displacement and vertical plate during the mounting.
(4) in addition, when the batch of printed boards and components is changed, SMT adhesive shall be used for marking.
3. Characteristics of patch adhesive:
1) connection strength: SMT adhesive must have a strong connection strength, after hardening, even in the solder melting temperature is not stripped.
2) spot coating: at present, the distribution of printed board is mostly using spot coating, so the glue is required to have the following properties:
(1) adapt to various mounting processes;
(2) easy to set the supply quantity of each component;
(3) simply adapt to changing the types of components;
(4) point coating quantity is stable;
3) adapt to high speed machine: now the use of the SMT must meet the point coating and high speed SMT machine high speed, specifically, is the high speed dot coating without wiredrawing, and then is the high speed paste, printed board in the transmission process, the adhesive of the SMT to ensure that the components do not move.
4) wire drawing and collapse: once the SMT adhesive sticks to the welding pad, the components cannot achieve electrical connection with the printed board, so the SMT adhesive must be coated without drawing, coated without collapse, so as not to contaminate the welding pad. Low temperature curing: when curing, the non-heat resistant plug-in components welded with wave soldering shall also pass through the reflow welding furnace, so the hardening conditions must meet the low temperature and short time.
5). Self-adjustment: in the process of reflow welding and pre-coating, the adhesive is to cure and fix the components before the solder dissolves, so it will prevent the components from sinking into the solder and self-adjustment. In view of this, Shanghai changxiang industrial co., LTD has developed a self-adjusting patch adhesive.
4. The curing of the adhesive can be done by uv and heat to cure the acrylic type, and there is only the heat curing of the epoxy type. Acrylic adhesive has advantages in short time hardening and low temperature curing. At present, the epoxy adhesive with low temperature and short time hardening has been developed to replace the propylene adhesive with poor adhesion. The choice of patch adhesive, or to fully consider the process mentioned before, the heat resistance of the components used, the life of the machine and other factors, choose the best product. The so-called life in the machine, refers to the adhesive patch left the closed, low temperature preservation conditions, exposure to the production line of the environment can be preserved for a period of time.
5.SMD adhesive pay attention:
To meet the needs of high-speed mounter to improve the production efficiency of mounting, the action speed of dispensing machine and mounter is increasing, from the initial 0.2 seconds/cycle of dot coating, the mounter speed has been developed to 0.1 seconds/cycle. What followed was the re-emergence of undesirable phenomena that had rarely appeared before, specifically.
1).Wire drawing caused by high-speed dot coating;
2).Angle deviation caused by high-speed mounting;
3).Offset in the x-y direction.
(1) wire drawing in order to overcome wire drawing, the setting of the high-speed temperature controller can be manually adjusted to force the physical properties of the adhesive, which will not affect the production speed, but also solve the problem.
(2) Angle deviation generally Angle deviation occurs in the SMT machine suction nozzle will be components on the point coated on the printed board adhesive, this is determined by the characteristics of the SMT, if you do not change the speed is difficult to solve this problem. Therefore, the best method is to choose suitable for high speed mounter mounter adhesive. The components absorbed by the mount head are difficult to move in the XY direction, but easy to rotate. For this reason, the design party of the patch adhesive shall be the adhesive components. At this moment, there shall be no shear stress causing the components to move.