There are many various difficulties in each of manual assembly and surface mount technology within soldering. For manual assembly a variety of these problems include disturbed joints which is when the solder moves as it’s solidifying. Another problem that commonly occurs is a ‘cold joint’ where the solder has been removed from the board too early and has not been allowed to melt properly. Another frequent problem is an overheated joint, which is where the solder has not yet flowed and the residue of the burnt flux makes this joint hard to fix.
Insufficient wetting is when the solder has wet the leads but then has not went on to form a good bond with the pad. There are also many problems with surface mount technology these include, solder balls which are mainly caused by poor process conditions which could include someone moving the board while the solder is settling. Another is solder beads which can occur when the reflow ramp up is either too fast or too slow. A further problem is bridging which can occur both due to hot slumping and cold slumping. As well as this another common problem is tombstoning which is most commonly caused by unequal components placement on the board before reflow results in unbalanced solder forces. Circuit boards are made up of extremely sensitive components, and moving them about in a careless manner will almost certainly cause the circuit board to break and no longer usable, especially putting tension on the small components, static electricity damages boards completely so the best way to prevent damage is to keep any sort of static electricity near the board to a minimum and discharge any static charge that has been built up in the circuit over time and hold the circuit board with care. While transporting boards you should wear rubber soled shoes in order to ground yourself before handling a board.
When you are in control of circuit boards you should make sure the humidity within your workspace is higher than normal as static electricity builds up much more and much faster in low humidity and in dry air. Also you are recommended to put on gloves to handle a circuit board. Solder paste is a material used in the creation of printed circuit boards to join surface mount components to pads on the board, it is also possible to solder through hole pin in paste components by printing solder paste over the holes. There are three kinds of solder paste deposition these are Step stencil which have the possibility of soldering all chip component types into cavities, also has a low cycle time and more space for different depths, the other kind is dispensing which has the possibility of soldering all chip component types into cavities, the cycle time of this depends on the needle which is used to create dispensed dot sizes and the third and final type is jetting, a jetting machine is capable for processes and for different volumes, a jetting machine is designed to feed a and place machine and can sometimes mount 40,000 components an hour. The most appropriate and cost effective method to use will depend on the final product confirmation since each method each have its own limitations in terms of capability to support design features or cycle time. Transferring solder paste in high density cavities is a process that can be done with high quality and capable of achieving IPC-610 class.
A pick and place machine helps with the assembly of circuit boards by automating of whereof small surfaces mount components on to boards, which then removes the process of manually planning and soldering small components while using pick and place preparation is key throughout soldering, solder paste must be applied to the solder pads of the board before operating the machine. Companies tend to use a laser cut vinyl strider as a mask with holds cut over the solder pads. Then with the mask on the board, solder paste can be forced onto the solder pads. The pick and place machine does exactly what the name states, it picks up the components and places them in a specified location. Solder paste is applied to the board before they are placed into the machine. Once the machine has placed the components the solder paste holds the components in place while the band is transferred to an oven.
When the solder paste is melted, reflowed and then cooled, permanent solder joints are created at each component, completing the process. Also the pick and place machine does not require an air compressor as it has a vacuum and pump within the machine.