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.

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