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.