soldering by chandrapro


									       his article deals with electronics manufacturing and prototyping techniques, see Wire
       wrap jewellery for the jewellery related topic

Close-up of a wire-wrap connection.

Manual wire wrapping/stripping tool and wire in various colours.

Wire stripper for AWG 30

Electrical wire wrap tool.

Manual tool to open a wire wrap connection.

Wrapped Z80 computer backplane 1977
Wrapped backplane (close-up)

Wire wrap is a technology used to securely attach to points for electrical or data contact. Wire
wrap is used in several industries.

In the circuit board manufacturing or prototyping it is method of constructing circuit boards
without having to have a printed circuit board manufactured. It can be made by hand or by
machine, and can be hand-modified afterwards. It was popular for large-scale manufacturing in
the 60s and early 70s, and continued to be used for short runs and prototypes until quite recently.

Wire wrap construction can produce assemblies which are more reliable than printed circuits —
connections are less prone to fail due to vibration or physical stresses on the base board, and the
lack of solder precludes corrosion, dry joints, etc. The connections themselves are firmer and
possibly have lower electrical resistance due to cold welding of the wire to the terminal post at
the corners.

Wire wrap construction became popular around 1960 in circuit board manufacturing, and use has
now sharply declined. Surface-mount technology and the increase in electronic switching speed
have made the technique much less useful than in previous decades. Solderless breadboards and
the decreasing cost of professionally made PCBs have nearly eliminated this technology.

In telecommunications wire wrap is in common high volume use in modern communications
networks for cross connects between copper wiring plant. For example, most phone lines from
the outside plant go to wire wrap panels in a central office, whether used for POTS phone
service, DSL or T1 lines. Typically at a main distribution frame Internal Cross Facilities
Assingments and External Cross Facilities Assigments, are connected together via jumpers that
are wire wrapped. Wire wrap is popular in telecommunications since it is one of the most secure
ways to attach wires, and provides excellent and consistent data layer contact. Wirewrap panels
are rated for high quality data services, including Category 5 grade wiring. The principal
competitor in this application is punch blocks, which are quicker but less secure.


        1 Overview
        2 Manual Wire Wrap
      3 Semiautomated Wire Wrap
      4 Automated Wire Wrapping
      5 Use of Electronic Design Automation
      6 See also
      7 External links

[edit] Overview
The electronic parts sometimes plug into sockets. The sockets are attached with cyanoacrylate
(or silicone adhesive) to thin plates of glass-fiber-reinforced epoxy.

The sockets have square posts. The usual posts are 0.025 inches (635 micrometres) square, 1
inch (25.4 mm) high, and spaced at 0.1 inch (2.54 mm) intervals. Premium posts are hard-drawn
beryllium-copper alloy plated with a 0.000025 inches (25 microinches) (635 nanometres) of gold
to prevent corrosion. Less-expensive posts are bronze with tin plating.

The two holes at the end of a manual wire wrap tool. The wire goes in the one near the edge, and
the post is inserted into the hole in the center.

30 gauge silver-plated soft copper wire is insulated with a fluorocarbon that does not emit
dangerous gases when heated. The most common insulation is "kynar".

The 30 AWG Kynar is cut into standard lengths, then one inch of insulation is removed on each

A "wire wrap tool" has two holes. The wire and one quarter inch (6.35 mm) of insulated wire are
placed in a hole near the edge of the tool. The hole in the center of the tool is placed over the

The tool is rapidly twisted. The result is that 1.5 to 2 turns of insulated wire are wrapped around
the post, and atop that, 7 to 9 turns of bare wire are wrapped around the post. The post has room
for three such connections, although usually only one or two are needed. This permits manual
wire-wrapping to be used for repairs.

The turn and a half of insulated wire helps prevent wire fatigue where it meets the post.
Above the turn of insulated wire, the bare wire wraps around the post. The corners of the post
bite in with pressures of tons per square inch (MPa). This forces all the gases out of the area
between the wire's silver plate and the post's gold or tin corners. Further, with 28 such
connections (seven turns on a four-cornered post), a very reliable connection exists between the
wire and the post. Furthermore, the corners of the posts are quite "sharp".

There are three ways of placing wires on a board.

[edit] Manual Wire Wrap

Typical wire wrap construction of Bell System telephone crossbar switch. Note some types of
connection were soldered.

A manual wire wrap tool resembles a small pen. It is convenient for minor repairs. Wire wrap is
one of the most repairable systems for assembling electronics. Posts can be rewrapped up to ten
times without appreciable wear, provided that new wire is used each time. Slightly larger jobs
are done with a manual "wire wrap gun" having a geared and spring loaded squeeze grip to spin
the bit rapidly. Such tools were used in large numbers in American telephone exchanges in the
last third of the 20th century, usually with a bigger bit to handle 22 or 24 AWG wire rather than
the smaller 28 or 30 AWG used in circuit boards and backplanes. The larger posts can be
rewrapped hundreds of times. They persisted into the 21st century in distribution frames where
insulation-displacement connectors had not taken over entirely. Larger, hand held, high speed
electric guns were used for permanent wiring, when installing exchange equipment between the
late 1960s when they replaced soldering, and the middle 1980s when they were gradually
replaced by connectorized cables.

                             BASIC SOLDERING PROCEDURE
Step 1      Check that your soldering iron tip is suitable for the Project. (no larger than the
            diameter of the pad).
            Check the tip is clean and shiny. If not, tin it by adding a small amount of
            solder to the tip.

Step 2      Adjust the temperature of the soldering station to 3500 C (degrees Celsius )

Step 3      Ensure the solder sponge is damp. A dry sponge will not clean the tip
            effectively, and one that is too wet will lower the temperature of the tip making
            for an ineffective solder joint.
Step 4    Carefully wipe the tip on the damp sponge until clean. Continually wipe the tip
          while soldering a circuit board.

Step 5    Bend the lead of the component
          using fine pliers so that it easily
          slides into the holes of the printed
          circuit pad.

Step 5    Insert the component to be soldered into the circuit board and bend the leads
          protruding from the bottom of the circuit board at an angle of approx 450.

Step 6    Cut the leads of the component close to the outer edge of the solder pad.

Step 7    When ready, hold the soldering iron at a 45 angle, and heat both the lead and
          the pad simultaneously. Touch the solder wire in the space between the iron
          tip and the lead.

Step 7    Keep the soldering iron tip still while moving the solder around the joint as it

Step 8    Remove the solder tip first and the solder wire next, (prevents spiking).
Step 9    Allow to the joint to cool naturally and undisturbed, do not blow on the solder
          joint to cool it.

Step 10   When you have completed all solder joints thoroughly clean your board, using
          Isopropyl Alcohol, and a bristle brush, to remove the flux residue and other

Step 11   Wipe or pat dry with a lint free tissue to remove traces of residue.

Step 12   Inspect for a good solder connection. The solder joint should be clean, smooth
          and shiny.

          The solder fillet should be concave in shape, feathering out smoothly to the
          edge of the pad. In the diagram below figure b) is the ideal solder joint.

          Figure a) the amount of solder applied is minimal and may result in a poor
          electrical connection over time.
          Figure c) indicates an excessive amount of solder has been applied to the
          connection. This may damage the solder pad due to excessive heat applied.

Step 13   Leave a large blob of solder on the tip when switching the iron off as this will
          protect the tip from oxidation and contamination.

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