Flux Coated Preforms

Features

• Eliminates the need for manual fluxing
• Eliminates excessive flux residue
• Increases productivity
• Applies flux precisely where it is needed
• Applies a uniform amount every time

Introduction

Flux Coated Preforms eliminate the costly production step of separate fluxing and increase throughput yields. Flux Coatings for Preforms are available in no-clean and rosin-based chemistries with a variety of activity levels to suit your substrate metallizations.

Flux Coatings

Indium Corporation’s unique coating process can control the amount of flux to tight tolerances. Flux Coatings are measured and applied by weight percentage. The coatings range from 1-3% and standard tolerances are controlled at +/- .5%. Coatings can be applied to most sizes and shapes of preforms.

Using Flux-Coated Preforms in Soldering

For certain soldering applications, flux coated preforms may offer the greatest number of benefits over other more conventional forms of solder. For applications other than active device manufacture, flux can be incorporated as an integral part of the preform design to meet customer needs for the precise amounts of flux, easy automation, and elimination of costly separate flux applications.

In general, fluxes should be avoided in active device assembly due to the difficulty in removing the flux residue after soldering. If care is taken to ensure the joining surfaces and the preforms are thoroughly clean, and if a reducing atmosphere at 350°C is used, flux coating is usually not necessary.

Flux coated Indalloy soft solder preforms eliminate the necessity of manually applying external liquid fluxes in operations such as vapor phase soldering of back-plane wiring assemblies and capacitor manufacture. Flux coated preforms are manufactured with the exact amount of flux required for the specific application, providing a high degree of consistency from one bond to another. Flux percentages can be specified between 0.5% and 3% by weight with a tolerance of ±0.5%. The most popular percentage being 1.0% by weight.

Indalloy flux types are available in non-activated pure gum rosin (type R), mildly activated rosin (type RMA) and fully activated rosin (type RA). RMA fluxes have a small but highly effective amount of an activator added to increase fluxing action over the R type. RA fluxes contain a small amount of an amine hydrochloride activator that provides superior fluxing action, as compared to R and RMA type fluxes. RA flux finds use in soldering assemblies where a high degree of fluxing action is desired, e.g. soldering to tarnished copper or nickel plate. RSA, an enhanced version, is also available for preform coating. This flux is the strongest of the rosin types. NC-7 and NC-9 fluxes are specially formulated RMA type fluxes that, along with the R type flux, leave nonconductive and non-corrosive residues that can safely be left on an assembly without fear of corrosion. However, for aesthetic or visual inspection purposes, the flux residue can be removed using a bipolar solvent to remove both the rosin portion and the ionizable activator portion of the flux. This is most often accomplished using vapor degreasing equipment.

In summary, the use of Indalloy flux coated preforms can result in the following advantages:

1. All fluxes used to coat preforms, when reflowed using a standard Sn63 profile, pass SIR tests.
2. The precise amount of flux and alloy are delivered to the solder joint.
3. The costly production step of separate fluxing is eliminated.
4. Bonding is faster because the flux is positioned where it is required, next to the surfaces to be joined, unlike the case with flux-filled preforms.
5. Because less flux is used, post solder cleaning is easier.
6. The flux quantity is uniform in thickness and consistent in amount from piece to piece.
7. The dull, flux-coated surface is ideal for IR reflow.
8. Since the flux on flux coated preforms contains no solvent, voiding is typically less than when manually applying liquid flux to uncoated preforms.