Mastering Assembly Consistency with InFORMS® Solder Preforms

Manufacturing modern electronics often feels like a balancing act—literally. Assembly tilt and uneven coplanarity are persistent headaches that compromise solder joints, leading to weak connections and potential product failures. When you are dealing with mass production, even a microscopic deviation in planarity can derail reliability.

Enter Indium Corporation’s InFORMS® solder preform technology: this innovative solution uses a reinforced matrix to deliver precision control, ensuring a uniform bondline every time. In this guide, we will break down why sizing is the critical factor for success and how to calculate the perfect dimensions for your application.

Understanding InFORMS® Technology

What Are InFORMS® Preforms?

At its core, InFORMS® technology is a reinforced matrix fabrication designed to solve the toughest soldering challenges. Unlike standard solder preforms, which are simply shaped alloy, InFORMS® incorporate a rigid structure within the solder itself. This design allows for a uniform bondline post-reflow, which is essential for high-reliability applications.

The benefits of adopting this technology are significant:

• Stronger Solder Joints: The reinforced structure improves the mechanical integrity of the connection.
• Longer-lasting Connections: Enhanced reliability means products last longer in the field.
• Repeatable Assembly: It removes the guesswork from mass production, offering consistent results across thousands of units.

For a deeper dive into the mechanics of the matrix and the science behind the technology, check out our detailed blog on Overview of InFORMS | indiumcorporation.

Design Guidelines: Sizing for Success

Implementing InFORMS® isn’t just about swapping out your old preforms; it requires precise sizing to work effectively. Because the matrix dictates the final bondline thickness, standard sizing rules do not apply directly.

The Dynamics of Reflow

When you design an assembly using InFORMS®, you must account for the physical changes that occur during reflow.

• Thickness Reduction: The initial thickness (Zi) of the preform is always thicker than the internal matrix. When the solder melts, the bondline collapses down to the height of the matrix (Zf).
• Lateral Expansion: Since the total volume of solder is not lost—it just changes shape—the preform will expand outwards. As the thickness reduces, the length and width of the footprint increases.

Pre- and Post-Reflow Considerations

The key to sizing is to work backward from your desired result. Do not size the preform based on what you want to place on the board; size it based on the post-reflow dimensions you need.

You need to determine:

1. Final Length (Lf) and Final Width (Wf): The area the solder will cover after reflow.
2. Final Thickness (Zf): The standoff height required, which is determined by the matrix type you select.

Selecting the Right Part First

Before you can calculate your initial dimensions for your InFORMS®, you must identify which part meets your standoff requirements. Different applications require different standoff heights. Whether you are dealing with power modules or large surface areas, there is a matrix configuration that fits.

Start by looking at your target Final Thickness (Zf)—this is your required bondline thickness. Match that requirement to the chart below to find the corresponding Part Description. This description will tell you the minimum initial thickness required for the part.

Here is a quick reference for common requirements:

Once you have selected the right category (like LM04 vs. LM08), you will know the initial thickness parameters needed to begin your backward calculation.

The Sizing Methodology

Now that you have your target part and know your final dimensions, you can calculate the correct preform size for your InFORMS®. This ensures you get the exact bondline control you need without solder overflow or insufficient coverage.

Note: The following calculation methodology is provided as a conceptual guide to help you understand the relationship between initial and final dimensions. While it offers a close approximation, Indium Corporation utilizes proprietary formulas for final product design to ensure optimal performance. Use this guide to understand the concept, but rely on our engineering team for the final specification.

Step-by-Step Calculation Logic

The calculation relies on the principle of Volume Consistency (V1 = V2). The volume of the solid preform before reflow must equal the volume of the solder joint after reflow.

To find your Initial Dimensions (Di) based on your Final Dimensions (Df), you can use the ratio of the thicknesses:

Where:

• Di = Initial Dimension (Length or Width)
• Df = Final Dimension (Length or Width)
• Zf = Final Thickness (Matrix Height)
• Zi = Initial Thickness

A Practical Example

Let’s walk through a real-world scenario.

Suppose you need a final solder joint with these dimensions:

• Final Length (Lf): 26.67mm
• Final Width (Wf): 22.10mm
• Final Thickness (Zf): 0.110mm

Step 1: Select the Part

Looking at the chart above, a final thickness of 0.110mm corresponds to an LM04 matrix type. For this specific InFORMS® matrix, the starting thickness (Zi) is 0.165mm.

Step 2: Calculate Initial Dimensions

Now, we plug these numbers into our formula to find the InFORMS® preform size we need to order:

Calculate Initial Length (Li):

Calculate Initial Width (Wi):

Step 3: Verify Volume Consistency

• Initial Volume: 21.78 * 18.05 * 0.165 = 0.064 mm³
• Final Volume: 26.67 * 22.10 * 0.110 = 0.064 mm³

So, to achieve your 26.67mm x 22.10mm footprint, you would order a preform roughly sized 21.78mm x 18.05mm.

Conclusion

InFORMS® solder preforms offer a sophisticated yet practical solution to age-old assembly problems. By strictly managing volume and dimensions through a reinforced matrix, manufacturers can eliminate tilt and achieve superior joint strength. While the sizing process requires a bit of backward calculation, the result is a predictable, high-yield soldering process that stands up to the demands of modern electronics.

Need Help Calculating Your Dimensions?

If you are facing specific design challenges or need assistance adjusting preform size and thickness, don’t guess. Contact Indium Corporation’s Technical Support Engineers at [email protected] for detailed assistance with InFORMS®, or visit www.indium.com to learn more about optimizing your assembly process.