Thorn Advice on the emergence of CHIP components (SMD)

Introduction

Some folk may find this article of use, read it in the context of being 1985.

With comparative difficulty the temptation to make play with the word ‘chips’ will be resisted. The subject matter to be covered in this article is that which concerns itself with the new miniaturised components which have been thus designated.

Accompanying the demand for ever more compact and lightweight Consumer Electronic equipment has been an increasing necessity for miniaturisation of both mechanical and electrical devices for these products. To meet this challenge, sub-miniature ‘chip’ parts have been developed, which reduce the size and weight of internal circuits.

In addition to flat- packaged ICs, chip parts are now being produced in the form of transistors, diodes, resistors & capacitors. Apart from the reduction in size of the parts themselves to save space and weight, suitable materials are now available which will stand the direct heat of the flow-solder bath. This means that components can be positioned on the ‘print’ side of the PC Board before the flow-solder process, instead of being added by hand subsequently in those few cases where it was deemed necessary.

New techniques are needed in the handling and replacement of chip components, including the use of
soldering instruments specifically designed for use with miniature devices.

Shown below are illustrations of typical chip components:

CHIP Components (SMD)

Handling Procedures

1. Particular care should be taken to avoid the ‘unbonding’
of print from the laminate due to overheating when
removing or replacing a component.

2. Use a thin-tipped, 15 to20W soldering iron with a
high insulation resistance to supply. The tip temperature
should lie between 250°C and 330°C.

3. When fitting a new component, do not apply the soldering
iron for more than three seconds and avoid using
‘rubbing’ strokes with the iron.

Excess heat can cause cracking of the component,
possibly altering the electrical rating or rendering the
device o/c. It should also be noted that the terminal
electrodes of chip resistors or capacitors are easily
dislodged.

4. Immediately before fitting new resistors or capacitors,
pre-heat the component to approximately 150°C. This is
to avoid thermal stress to the part being fitted.

5. Never refit a chip component even if, after removal, tests
show that it is not faulty.

6. Although, in production, adhesive is used to keep
components in place before soldering this is only because
they will be hanging on the underside of the board whilst
it is passing down the production line and over the solder
bath. Adhesive is not necessary under field service
conditions.