Low Cost Automation Tutorial

#156 Production Technology Improvement Course for Mechanical Designers - 26: Soldering Tact Time Reduction Method

Category : Automation elements technology

April19, 2013

The important point in assembly/mounting production technology is to supply appropriate heat energy to stabilize the melting metal at targeted temperature. However, sudden heat rise can result in mounting failure due to uneven heat conduction and large residual stress, causing degradation of durability quality. On the other hand, production techniques to reduce production tact time are also needed.
Here, representative tact time reduction methods of mounting technology are explained.

(1) Fundamentals of mounting technology: About self-alignment effects

Self positioning movement of the part that naturally occurs while the melting solder solidifies is called "Self-alignment effect".

On PCBs, preliminary solder spots are deposited where the parts are to be soldered. The self-alignment effect utilizes a phenomenon where the preliminary solder spots position the light weight parts into proper positions by melting solder's surface tension.

Adhesive flux is applied on the preliminary solder spots, and the parts are temporarily affixed on the preliminary solder spots by the adhesiveness of the flux.

The following production techniques are needed to gain the self-alignment effect.

a) Stability of preliminary solder position and amounts
b) Stability of flux application position, amounts, and adhesiveness
c) Uniformity of soldering heat conduction

[Photo 1] Self-aligned chip part (Right) and defective soldering (Left)

(2) Tact time reduction method of mounting technology

In order to reduce the tact time while maintaining uniform heat conduction, mounting fixtures are preliminarily heated.

Aim of preliminarily heating

a)	By preliminarily heating the mounting fixtures, heat application time to solder melting is reduced.
b)	By moderating the temperature change, the residual stress is suppressed.
c)	Highly accurate stabilization of solder melting temperature by uniform heat conduction.

Pre-heating table (MISUMI, hot plate: HTPL, [Fig.1]), Sheathed heater (MISUMI: MCHG, [Fig.2]), Temperature controller (MISUMI, Temperature controller: MTCS, [Photo 2]) can be utilized.

In order to make fixture side heat conduction uniform and accelerate, heat insulation material (EX.: Epoxy Glass Plates: EPXA) and heat transfer material (EX.: aluminum plate: A5052P) are used in designs.

[Fig.1] Example of a hot plate, [Fig.2] Construction of a sheathed heater, [Photo 2] Temperature controller

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