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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.

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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.

 

Reflow
soldering is an operation which is dependent on contained heat to melt the
solder to lead to joints connecting, prior to this a solder paste is used to
attach multiple electrical components for a short time to their bond pads. Heating
may be achieved by putting the assembly through a reflow oven or by soldering individual
joints with a hot air pencil. Reflow soldering is the most well-known method of
connecting surface mount components with a circuit board. The aim of the reflow
process is to melt the solder and heat the touching surfaces without
overheating and damaging the electrical components. There are 4 sections of
reflow soldering these are; preheat zone, thermal scale zone, reflow zone and
cooling zone. Preheat zone is the first stage of the reflow process, during
this reflow phase, the entire board assembly climbs towards a target soak or
dwell temperature. The overall goal of the preheat section of the process is to
get the entire assembly safely and consistently to a soak or pre-reflow
temperature. The second stage is thermal soak zone which usually takes around
1-2 minutes to remove the solder paste and the flux components start the oxide
reduction process on the component leads and pads. The third stage is the
reflow stage where the temperature reaches its highest point. The final zone is
a cooling zone which slowly cools the board and finally solidifies the joints
on the solder.

 

According to website ‘copperplumbing.org.uk’
they say you should clean both outside and inside of the surface of the
fitting. They recommend using fine sand paper or a brush but go against the use
of steel wool. They also recommend Abrasive impregnated nylon scouring pads for
potable services in order to prevent particles of steel entering the system.
According to website ‘http://www.youtube.com/watch?v=s4uK21E1xXk’ using a
new proprietary technology, magic cleaner 3D manages to remove particulates
attached to printed circuit boards, this made it the most powerful cleaner in
the world when the video was released in 2011. As the years go on the size of
the components used are becoming much smaller whilst the density of components
on the PCB is increasing. There are 2 types of cleaners they are the brush type
cleaner and adhesive roller type cleaners. Flux is necessary to reduce oxide
when there are hot metals in contact in the air, many pieces of solder normally
have flux in the center of them. Which is more helpful as it manages to reduce
oxide of the hot metals as when the solder melts it can reduce the oxide almost
instantly.

 

Lead
forming machines and lead forming tools performs both the same tasks lead
forming and lead cutting tasks. Manual and motorized component lead farmers accommodate
a wider range of axial and radical through hole components. There are many
different things that affect lead forming these include; the length of the lead
foot, the length of lead tip to lead tip, the thickness of the leads and the
length of the component body to the first bend in the lead, lead thickness is
the most important of the conditions. 

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