There aremany various difficulties in each of manual assembly and surface mounttechnology within soldering.
For manual assembly a variety of these problemsinclude disturbed joints which is when the solder moves as it’s solidifying.Another problem that commonly occurs is a ‘cold joint’ where the solder hasbeen removed from the board too early and has not been allowed to meltproperly. Another frequent problem is an overheated joint, which is where thesolder has not yet flowed and the residue of the burnt flux makes this jointhard to fix. Insufficient wetting is when the solder has wet the leads but thenhas not went on to form a good bond with the pad. There are also many problems withsurface mount technology these include, solder balls which are mainly caused bypoor process conditions which could include someone moving the board while thesolder is settling. Another is solder beads which can occur when the reflowramp up is either too fast or too slow. A further problem is bridging which canoccur both due to hot slumping and cold slumping. As well as this another commonproblem is tombstoning which is most commonly caused by unequal componentsplacement on the board before reflow results in unbalanced solder forces.
Circuit boards are made up of extremely sensitivecomponents, and moving them about in a careless manner will almost certainlycause the circuit board to break and no longer usable, especially puttingtension on the small components, static electricity damages boards completely sothe best way to prevent damage is to keep any sort of static electricity nearthe board to a minimum and discharge any static charge that has been built upin the circuit over time and hold the circuit board with care. Whiletransporting boards you should wear rubber soled shoes in order to groundyourself before handling a board. When you are in control of circuit boards youshould make sure the humidity within your workspace is higher than normal asstatic electricity builds up much more and much faster in low humidity and indry air. Also you are recommended to put on gloves to handle a circuit board. Solderpaste is a material used in the creation of printed circuit boards to join surfacemount components to pads on the board, it is also possible to solder throughhole pin in paste components by printing solder paste over the holes. There arethree kinds of solder paste deposition these are Step stencil which have thepossibility of soldering all chip component types into cavities, also has a lowcycle time and more space for different depths, the other kind is dispensing whichhas the possibility of soldering all chip component types into cavities, thecycle time of this depends on the needle which is used to create dispensed dotsizes and the third and final type is jetting, a jetting machine is capable forprocesses and for different volumes, a jetting machine is designed to feed a and place machine and can sometimesmount 40,000 components an hour. The most appropriate and cost effective methodto use will depend on the final product confirmation since each method eachhave its own limitations in terms of capability to support design features orcycle time. Transferring solder paste in high density cavities is a processthat can be done with high quality and capable of achieving IPC-610 class.
A pick andplace machine helps with the assembly of circuit boards by automating of whereofsmall surfaces mount components on to boards, which then removes the process ofmanually planning and soldering small components while using pick and place preparationis key throughout soldering, solder paste must be applied to the solder pads ofthe board before operating the machine. Companies tend to use a laser cut vinylstrider as a mask with holds cut over the solder pads. Then with the mask onthe board, solder paste can be forced onto the solder pads. The pick and placemachine does exactly what the name states, it picks up the components andplaces them in a specified location.
Solder paste is applied to the boardbefore they are placed into the machine. Once the machine has placed thecomponents the solder paste holds the components in place while the band istransferred to an oven. When the solder paste is melted, reflowed and thencooled, permanent solder joints are created at each component, completing theprocess. Also the pick and place machine does not require an air compressor asit has a vacuum and pump within the machine. Reflowsoldering is an operation which is dependent on contained heat to melt thesolder to lead to joints connecting, prior to this a solder paste is used toattach multiple electrical components for a short time to their bond pads. Heatingmay be achieved by putting the assembly through a reflow oven or by soldering individualjoints with a hot air pencil.
Reflow soldering is the most well-known method ofconnecting surface mount components with a circuit board. The aim of the reflowprocess is to melt the solder and heat the touching surfaces withoutoverheating and damaging the electrical components. There are 4 sections ofreflow soldering these are; preheat zone, thermal scale zone, reflow zone andcooling zone. Preheat zone is the first stage of the reflow process, duringthis reflow phase, the entire board assembly climbs towards a target soak ordwell temperature. The overall goal of the preheat section of the process is toget the entire assembly safely and consistently to a soak or pre-reflowtemperature. The second stage is thermal soak zone which usually takes around1-2 minutes to remove the solder paste and the flux components start the oxidereduction process on the component leads and pads. The third stage is thereflow stage where the temperature reaches its highest point. The final zone isa cooling zone which slowly cools the board and finally solidifies the jointson the solder.
According to website ‘copperplumbing.org.uk’they say you should clean both outside and inside of the surface of thefitting. They recommend using fine sand paper or a brush but go against the useof steel wool. They also recommend Abrasive impregnated nylon scouring pads forpotable services in order to prevent particles of steel entering the system.
According to website ‘http://www.youtube.com/watch?v=s4uK21E1xXk’ using anew proprietary technology, magic cleaner 3D manages to remove particulatesattached to printed circuit boards, this made it the most powerful cleaner inthe world when the video was released in 2011. As the years go on the size ofthe components used are becoming much smaller whilst the density of componentson the PCB is increasing. There are 2 types of cleaners they are the brush typecleaner and adhesive roller type cleaners.
Flux is necessary to reduce oxidewhen there are hot metals in contact in the air, many pieces of solder normallyhave flux in the center of them. Which is more helpful as it manages to reduceoxide of the hot metals as when the solder melts it can reduce the oxide almostinstantly. Leadforming machines and lead forming tools performs both the same tasks leadforming and lead cutting tasks. Manual and motorized component lead farmers accommodatea wider range of axial and radical through hole components. There are manydifferent things that affect lead forming these include; the length of the leadfoot, the length of lead tip to lead tip, the thickness of the leads and thelength of the component body to the first bend in the lead, lead thickness isthe most important of the conditions.