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Products > Packages > Semiconductor Device Mount Manual > SOLDERING GENERAL > Materials for Mounting >

CHAPTER 1 SOLDERING GENERAL


1.5 Materials for Mounting
1.5.2 Flux

Flux is used in the soldering process for the following purposes.

· To remove oxidants from the surface of the component or the surface of the pattern
· To prevent re-oxidation during soldering
· To reduce the surface tension of molten solder

In other words, flux is used to improve the solderability.


There are two broad categories of flux: rosin based and aqueous based.

Rosin based flux can be divided into the following three types, based on differences in activation.

Table 1-5-1. Rosin Based Flux Types
R type (Rosin base) Inert rosin flux. Non-corrosive.
RMA type
(Mildly Activated Rosin base)		 Mildly activated rosin flux. Non-corrosive. Better solderability than R type.
RA type
(Activated Rosin base)		 Mildly activated rosin flux. Better solderability than R and RMA types, but more corrosive.


R type is generally used most, but many types of solder paste contain the RMA type flux.

Aqueous flux generally contains a large amount of chlorine, and is therefore less suitable for semiconductors due to the possible effects on device reliability.

Even if rosin flux is used, substances left in the residue after soldering may, when exposed to high temperatures or humidity, cause corrosion of the conductive parts of the leads or wiring board, or a reduction in conductor insulation.

To 1.5.1 Printed Wiring Board (PWB)To 1.5.3 Solder paste