iMaps Announcements 09/2025

THT solder joints: Why DfM rules alone are not enough - Hidden risks and costs of Through Hole Technology

by Dr.-Ing. Reinhardt Seidel, DEEPTRONICS GmbH

Hidden THT risks

PCB designers know the problem: even if all DfM rules are strictly adhered to, unexpected THT soldering problems arise in series production. Especially with high-power electronics with several copper layers and thick PCBs (>1.6 mm), the limits of conventional design-for-manufacturing approaches become apparent.

The reality is that the majority of THT risks are not covered by standard DfM checks. This gap is particularly wide in the case of sophisticated high-power assemblies, because the effects of PCB design are particularly pronounced here.

This leads to costly prototype loops, rework and delays.

The physics behind the problem

THT solder joints are complex multi-physical systems. Their quality depends on numerous factors that influence each other:

• Thermal mass: copper layers, PCB thickness and component size
• Process parameters: Soldering time, temperature profiles, flux and alloy
• Geometric influences: Pin-to-hole ratio, bumper connection and distribution
• Machine specifics: process type, nozzle configuration, wave height, preheating

Conventional DfM rules do not consider these factors adequately, but define simple rules that usually only define minimum distances or a hole diameter. However, it is the interaction between the assembly design and the soldering process that determines the actual solderability.

Identify risks through process-based calculation instead of estimation

What if you knew at the design stage which solder joints would be problematic? What if you could quantify how design changes affect manufacturability?

A digital twin of the THT soldering process makes exactly that possible. It simulates the process physics and evaluates each solder joint individually:

• Green solder joints: < 5 s robust process window
• Yellow solder joints: 5-7 s iterative process development required
• Red solder joints: > 7 s high risk of insufficient soldering

Risk minimization at the design stage for high quality requirements

The physics-based approach of the Solder Copilot supplements the subjective assessment by manual checking with quantified risk assessment. Critical THT solder joints are identified before layout freeze and prototype ordering and defects are corrected before they become costly.

The result

Fewer prototype loops, faster time to market and higher production quality.

Indications of hidden risks can be identified using simple rules of thumb:

1. Thick PCBs (>1.6 mm) with many copper layers (>4 layers)
2. Thick copper layers > 35 µm
3. High-power components (electrolytic capacitors, shunts, transformers)
4. Use of solder masks for wave and selective wave soldering with dense placement

Program Autumn Conference at Munich University of Applied Sciences

We are once again inviting you to the fall conference in Munich on October 16 and 17, 2025. As usual, the venue will be the "Roter Würfel" lecture hall at Munich University of Applied Sciences. We look forward to your participation. You can find the detailed program at https://www.conftool.net/imaps-herbstkonferenz-2025/sessions.php (see QR code)

Calendar of events

IMAPS Germany - Your association for packaging and packaging technology

IMAPS Germany, part of the "International Microelectronics and Packaging Society" (IMAPS), has been the forum in Germany for all those involved in microelectronics and packaging technology since 1973. With almost 250 members, we essentially pursue three important goals:

• we connect science and practice
• we ensure the exchange of information among our members and
• we represent the point of view of our members in international committees.

Imprint

IMAPS Germany e. V.
Kleingrötzing 1, D-84494 Neumarkt-St. Veit

1st Chairman: Prof. Dr.-Ing. Martin Schneider-Ramelow, Director of the Fraunhofer Institute for Reliability and Microintegration (IZM), This email address is being protected from spambots. You need JavaScript enabled to view it.

Treasurer
(for questions about membership and contributions):
Ernst G. M. Eggelaar, This email address is being protected from spambots. You need JavaScript enabled to view it.

You can find detailed contact information for the members of the Executive Board at www.imaps.de
(Executive Board)