Preforms

Solder Preforms are used in a variety of applications that require precise amounts of solder.

Preforms come in standard shapes such as squares, rectangles, washers and discs. Typical sizes range from .010" (.254mm) up to 2" (50.8mm). Smaller and larger sizes, as well as custom shapes, are also available. Dimensions can be held to tight tolerances to assure volume accuracy.

Selecting Alloys

A wide assortment of alloys is available in liquidus temperatures that range from 47°C to 1063°C. Alloys can be indium-contained, gold-contained, lead-free, fusible or standard tin-lead, as well as many others.

1. Alloy selection should be based on strength and other required physical properties, as well as the preferred soldering temperature and the operating temperature of the device being soldered. A general rule is to select an alloy that melts at least 50°C higher than the operational temperature of the part being soldered.
2. Next, consider the materials being soldered and what solder is most compatible with them. For example, tin-based solders will scavenge the gold from gold-plated parts, forming brittle intermetallics, so indium-based solders are generally recommended in these cases.
3. Metals and alloys have different characteristics that can affect the ease with which they can be made into different shapes and thicknesses. It is important to consider the shape of the final preform in the alloy selection process.
4. The operating environment of the completed assembly is also an important consideration for alloy selection. Will it operate in very high or very low temperatures, or be subjected to vibration? If so, you need to select an alloy that will stand up to these conditions.

Our Application Engineers will work with you to determine the best alloy for your application.

Selecting Dimensions

The location of the solder joint and the volume of solder needed will determine the size and shape of the preform. Once the flat dimensions (diameter, length, width) have been determined, the thickness can be adjusted to achieve the desired volume of solder. Generally, for through-hole connections, add 10-20% to the calculated volume for a good fillet. For pad to pad joints, figure about 5% less surface area than the pad.

Each Solder Preform should have a burr tolerance specified. You should stay as close to standard tolerances as possible to avoid adding cost and lead time to your preforms.

Indium Corporation has an extensive library of sizes and shapes from which you can choose, or we can create a set-up specifically for your application. Using an existing preform size can eliminate the additional time associated with creating a new set-up.

Packaging and Storage

Solder Preforms come in a variety of packaging options, including tape and reel. To minimize excessive handling, and exposure to air and subsequent oxidation, Solder Preforms should be packaged according to the quantity used during a typical work shift.

Store in the original container, closed securely, in 55% RH or less and at temperatures less than 22°C. Solder Preforms can also be stored in an inert atmosphere, such as a nitrogen dry box.

Shelf Life

The shelf life of solder preforms is dependent on the alloy composition. Pb-free alloys, and alloys with lead content of less than 70%, have a shelf life of 1-year from the date of manufacture (DOM). Alloys with lead content >70% have a shelf life of 6-months from the DOM.

Dimensional Specification Recommendations

Width/length or diameter:	Typical Tolerances
Up to .100" (2.54mm)	±.002"(± .051mm)
Over .100" (2.54mm)	± .005" (± .127mm)
Thickness:
Up to .001" (.025mm)	± .0002" (.005mm)
.001" (.025mm) to .002" (.050mm)	± .0003" (.0076mm)
> .002" (.050mm) to .010" (.254mm)	± .0005" (.0127mm)
> .010" (.254mm) to .020" (.508mm)	± .0010" (.0254mm)
> .020" (.508mm) to .050" (1.27mm)	± .0025" (.0635mm)
> .050" (1.27mm)	± 5%
Burr Tolerances (Discs, Squares & Rectangles):
≤.050" (1.27mm)	.002" (.050mm)
>.050" (1.27mmm) to .500" (12.7mm)	.003" (.076mm)
>.500" (12.7mm)	.005" (.127mm)
Burr Tolerances (Washers & Frames):
≤.100" (2.54mm)	.003" (.076mm)
When thickness ≥ 2/3 of I.D.	.005" (.127mm)

Flux Coatings for Solder Preforms

Features

1. Eliminates the need for manual fluxing
2. Eliminates excessive flux residue
3. Increases productivity
4. Applies flux precisely where it is needed
5. 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.

Flux	IPC Classification	Substrate Finishes	Reliability J-STD-004
NC-7	ROL0	Au,Ag,Pd,Pt,Cu	Pass
NC-9	ROL1	Sn,NiAu,SnPb,Cu	Pass
R	ROL0	Au,Ag,Pd,Pt	Pass
RMA	ROL0	Sn,NiAu,SnPb,Cu	Pass
RA	ROL1	Cu,Ni, Cu Alloys (Brass, Bronze)	Cleaning Recommended
RSA	ROL1	Cu,Ni, Cu Alloys (Brass, Bronze)	Cleaning Recommended