4 Vapor Phase Reflow Profiling. 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

4 VAPOR PHASE REFLOW PROFILING

There are many driving forces for the use of vapor-phase soldering (VPS), also known as condensation soldering:

• Fixed peak temperature (215 °C or 230 °C) o

Includes very large and small components with wide variances in thermal mass o

Large and small components both achieve almost the same peak temperature

•

Temperature-sensitive components

•

Pb-free alloys with higher melting points

• Excellent heat-transfer capability

• Inert environment

• Vacuum capability (in some machines)

• Preheat as an integral part of the machine

• Possibility for lower intermetallic (IMC) thickness due to lower peak temperature

• Potential for lower voids if vacuum capability is used

•

Better PWBA cleanliness

•

Higher surface insulation values

•

VPS liquids can access tighter spaces to remove flux residues

Even with these driving forces, VPS has gone through changes in popularity. It was the process of choice in the early 1980s, but its use declined considerably for several reasons, including problems with the VPS process itself and improvements in IR processes. Convection-dominant IR system have been known to provide efficient heating without the inherent problems of VPS.

By the late 1980s, VPS almost disappeared entirely due to excessive incidences of wicking on leads of J- and gullwing devices, which led to solder opens. This wicking was caused by the lead and the land heating at different rates during VPS; it was exacerbated by noncoplanarity (the failure of the lead to touch the land). The surface of the lead reached the solder melting point a few seconds before the surface of the land, which caused the solder paste to melt, wet and wick up the lead before the land became hot enough for the molten solder to wet it. By the time the land reached the melting point of the solder paste, there was not enough solder left on the land to form a good solder joint. In addition to wicking in leaded parts, especially J-lead devices, VPS has also been known to cause tombstoning in chip components.

Figure 4-1 shows a VPS profile showing the leads reaching melting point temperature sooner than the pad. This time delay in reaching melting point for J-leaded components caused wicking and opens in solder joints. Newer

VPS systems with built-in preheat have made this wicking less of a concern (see Figure 4-2). Additionally, the superheat (temperature between melting point and Peak Reflow) is significantly reduced in Pb-free processes to around 40 °C in SnPb alloys and around 20 °C in SAC Pb-free alloys.

VPS uses the latent heat of liquid vaporization to provide heat for soldering. This latent heat is released as the vapor of the inert liquid condenses on component leads and PCB lands. This liquid produces a dense, saturated vapor that displaces air and moisture. The temperature of the saturated vapor zone is the same as the boiling point of the vapor phase liquid. This fluid does not have any environmental concerns.

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

Figure 4-1 VPS Profile Showing Wicking and Opens

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.