3.1.1 Preheat Zone. IPC IPC-7530A

IPC-7530A provides guidelines for developing thermal profiles to produce acceptable tin-lead and lead-free electronics assemblies. It is a comprehensive document which covers various aspects of temperature profiling for mass soldering processes, including reflow and wave soldering. This document is intended for managers, design and process engineers and technicians who deal with mass soldering processes.

PDF

Document

IPC-7530A reliability.

Draft Document for Industry Consensus Only August 2016

Figure 3-5 Example of Ramp to Soak and Then to Peak Top) and Ramp to Peak Profiles

There are four major zones in a reflow profile discussed in the following.

3.1.1 Preheat Zone

The temperature in the preheat zone can range from 30 °C to 175 °C. Many component suppliers generally recommend a 2 °C to 4°C /second ramp rate to avoid thermal shock to sensitive components. Such guidelines are considered conservative since some capacitors are wave soldered where they go from preheat temperature of about 120 °C to wave pot temperature of 260 °C. The fast ramp rate increases the potential for solder balls, so it should be kept as low as feasible with consideration given to the acceptable ramp rate of the most sensitive component on the assembly.

3.1.2 Thermocouple Attachment

Figure 3-6 shows recommended locations of thermocouples on a board. It is important that thermocouples be attached onto small and large components at the solder joints. For BGAs, it is also important to attach a thermocouple at the top of the package.

IPC-7530A Draft Document for Industry Consensus Only August 2016

Figure 3-6 Locations of Thermocouples on a Board With Large and Small Components

In developing any profile, it is very important to use the right thermocouple. Type k thermocouples with wire gauge of 36 American wire gauge (AWG) should be used. Thicker thermocouple wires can act as a heatsink and affect temperature readings. Thermocouple wire length should not exceed three feet for good accuracy. To ensure accuracy, thermocouple junctions must be welded. No twisting, crimping or soldering should be used.

Care should be exercised when using high-temperature tapes such as polyimide or aluminum. Tapes tend to come loose during reflow, and the system then measures the temperature of the air in the oven and not the temperature of the solder joints. It is important to make sure there is good contact of the tape; alternately, a hightemperature solder or thermally conductive adhesive can be used to attach thermocouples to the solder joints.

One benefit with using tape is that the thermocouples can be reused repeatedly without damaging them.

Peak temperature readings should be extracted from thermocouples placed at/near the center of the package for assembly that is in a live-bug orientation. In some cases, drilling a hole into a package may be necessary for advanced constructions (2D/3D assemblies or ones with integrated heat spreader or heatsink). For a dead-bug orientation, verification of peak temperature within +/- 2 °C of the live-bug reference is recommended. Refer to

JEP140 for thermocouple use. Four to six thermocouples should be attached at various component locations to represent the lowest to highest thermal mass areas, including at least two thermocouples for BGAs. Figure 3-7 shows locations of thermocouples on a BGA.

Figure 3-7 Recommended Locations of Thermocouples on a BGA

Use of high-temperature solder or thermally conductive adhesive to attach thermocouples to solder joints is a very good approach. If high temperature soldering is not an option because of material availability or soldering difficulties, use of aluminum or copper tapes works well.

In cases of BGAs, as shown in Figure 3-8 and Figure 3-9, drill holes in the inner and outer rows of the BGA pads from the bottom of the board and push the thermocouples almost to the top surface to correctly measure the temperature of BGA balls. BGA ball temperatures of inner and outer rows should be within 2 °C.

IPC-7530A Draft Document for Industry Consensus Only August 2016

Proper attachment is critical to ensure an accurate temperature measurement is achieved. There are various methods for attaching thermocouples to assemblies for profiling.

Figure 3-8 Example of TC on Inner and Outer Rows – Drilling From Bottom of BGA and Other Components

Key features

Thermal Profile Development for Mass Soldering
Reflow and Wave Soldering Processes
Temperature Profiling Requirements
Guidelines for Solder Alloy Selection
Optimizing Profiles for Different Applications
Solder Joint Quality and Reliability
Troubleshooting Common Soldering Defects

Frequently asked questions

The primary purpose of this document is to provide practical information to those responsible for developing thermal profiles for mass soldering processes, including reflow and wave soldering. It aims to ensure the production of high-quality solder joints by optimizing the temperature profile during the soldering process.

Temperature profiling is crucial for ensuring consistent and reliable solder joints. It helps to control the heating and cooling rates during the soldering process, preventing damage to components and the printed wiring board (PWB). A well-defined thermal profile ensures that all solder joints reach the required temperature for proper metallurgical bonding.

This document primarily focuses on two common mass soldering processes: reflow soldering and wave soldering. It provides specific guidelines for developing thermal profiles for both processes, considering the unique characteristics and challenges of each.

IPC-7530A provides guidelines for developing profiles that accommodate both tin/lead and lead-free components. It highlights the importance of considering the different melting points and temperature requirements of each type of component during profile development.

User questions

Patricia K.

What factors are important when creating a wave soldering thermal profile?

The solder alloy and flux limitations, component and substrate specifications including their limitations, web width for conveyor speed calculation, preheat zone temperature settings, solder pot temperature setting, and cooldown settings are crucial factors for developing a wave soldering thermal profile with preheat, soldering, and cool down phases.

Linda L.

How can heat sink effects be minimized during mass wave soldering?

Use thermal relief for large metallic planes like ground planes to minimize thermal sinking and ensure even heat distribution.

Linda L.

How can good soldering quality be ensured with surface mount components in mass wave soldering?

Align surface mount components parallel to the wave to ensure smooth solder flow and consistent contact with component leads.

Linda L.

What are considerations for using selective wave soldering pallets?

Ensure adequate clearance for components and proper alignment to prevent soldering failures. Proper clearance for older components and proper alignment for surface mount components are crucial.

Linda L.

How can component movement be prevented during mass wave soldering?

Secure large components like connectors and sockets to prevent movement and avoid misalignment or damage during soldering.

Mary J.

What is the lifespan of a type K thermocouple?

The viewed document does not specify the lifespan of a type K thermocouple. However, the lifespan of a standard thermocouple and sample board is estimated at 15-30 profiles, depending on factors such as PWB thickness and laminate type. Reattaching the thermocouple to multiple assemblies reduces lifespan to 3-5 profiles.

Linda L.

How does the distance of soldering connections to the PWB edge affect mass wave soldering?

The distance from soldering connections to the PWB edge affects heat conduction and the thermal profile. Connections should be sufficiently far from the edge to prevent soldering problems.

Linda L.

How does PWB rigidity at maximum soldering temperature impact mass wave soldering?

PWB rigidity affects its ability to withstand heat and deformation during soldering. A rigid PWB helps maintain a consistent thermal profile, ensuring good soldering quality.

Michael I.

What are the guidelines and requirements in IPC-7530A for creating thermal profiles in mass soldering processes?

IPC-7530A provides guidelines and requirements for developing thermal profiles to ensure high-quality solder joints in reflow and wave soldering. It covers key terms, profiling methods for various soldering types, temperature profiling tools, and troubleshooting soldering defects.