3.1.5 Cooling 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.

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

60 to 90 seconds but closer to 60 seconds. Extended duration above the solder melting point or TAL will damage temperature-sensitive components. It also results in excessive intermetallic growth, which makes the solder joint brittle and reduces solder joint fatigue resistance.

3.1.5 Cooling Zone

The typical cooling rate for most assemblies has been 4 °C to 6 °C per second, driven primarily by throughput and

SnPb intermetallic thickness concerns. With the transition to Pb-free solders the pad cratering defect has become more common due to the increased stiffness of SAC solders and the reduction in the flexure resistance and fracture toughness of laminates. Pad cratering has been identified directly after the reflow process, leading to several experiments designed to understand the impact of cooling rate. Among others such as package warpage, pad cratering is one of the reasons for many companies using lower temperature lead free solders containing bismuth (Table 3-1)

During the cooling phase, the various materials will cool at different rates. The BGA package typically will cool faster than the solder joint and much faster than the PCB. This differential cooling can create mechanical strain on the weakest spot in the interconnect, the laminate below the BGA pad. By slowing the cooling rate significantly, to as low as 1.5 °C per second, all of the materials will cool more slowly and will reduce the strain placed on the laminate. Experimental work performed by consortia has shown that this slowed cooling does not appear to negatively impact solder joint intermetallics nor the grain structure of the joint. If pad cratering is found immediately after reflow or if the assembly is determined to be at risk for cratering, then the cooling rate of the

PCBA should be slowed to reduce strain.

3.1.6 Thermal Profile for Backward Compatibility

Developing a reflow profile is made difficult when dealing with backward compatibility issues in which some leadfree components are used on a primarily tin/lead board. Backward compatibility is a scenario in which some components are available only with lead-free surface finishes. Such a scenario arises since it may not be economical for many component suppliers to supply both tin/lead and lead-free versions of the same component.

It is not an issue when using leaded components such as small outline integrated circuit (SOIC), plastic leaded chip carrier (PLCC) or fine pitch with lead-free surface finishes. Most tin/lead components primarily have 85 % tin surface finish with about 15 % lead.

The real problem arises when using lead-free BGAs on a primarily tin/lead board. If the tin/lead profile with maximum peak temperature of 220 °C is used, the lead-free BGA balls will not reflow at all or will partially reflow, creating a serious solder joint reliability problem.

If tin/lead components are soldered along with some lead-free BGAs in the same oven (since tin/lead versions are not available), a peak temperature must be used that is not damaging to all the tin/lead components, but is also sufficient to reflow the lead-free BGAs. Using tin/lead solder paste is appropriate, since most of the components on the board are tin/lead. As shown in Table 3-1, peak temperature of 210 °C to 220 °C will be fine for tin/lead but inadequate for lead-free BGA balls with a melting point of 217 °C to 221 °C. But a peak temperature of 228 °C to

232 °C with 60 to 90 seconds TAL will be sufficient to reflow lead-free BGAs without seriously damaging all the tin/lead components on the same board.

If the tight reflow temperature band of 228 °C to 232 °C is difficult to achieve to solder both tin/lead and lead-free

BGAs in backward compatibility scenarios, then consider selective laser soldering to solder lead-free BGAs after other tin lead components have been soldered in a convection reflow oven or find an alternative source for BGAs with tin/lead balls.

3.1.7 Unique Profile for Each PWBA

A reflow program is not the same as a reflow profile. A reflow program is the combination of machine settings and conveyor speed, while a reflow profile is the visual representation of the time and temperature that a thermocouple sees during a PWBA’s travel through the reflow oven. Every unique PWBA needs to be profiled to show that all locations on the board meet the various requirements for creating acceptable solder joints. A single program will produce very different profiles for different, unique PWBAs. There is some misunderstanding that one

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.