1.4.16 Preheat. 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

1.4.16 Preheat

The section of the soldering equipment which establishes the ramp rate for an assembly before the soak.

A profile zone where the assembly is heated from room temperature to the beginning of the soak zone temperature and is characterized by the ramp slope measurement.

1.4.17 Class 1 Radiant IR-Dominant Systems

Heating of the assembly is accomplished predominantly by infrared (IR) radiation with little or no convection.

1.4.18 Class 2 Convection/IR Systems

Heating of the assembly is accomplished by a combination of IR radiation and convection in varying ratios.

1.4.19 Class 3 Convection-Dominant Systems

Heating of the assembly is accomplished predominantly by convection with little or no IR.

1.4.20 Profile Zones

The profile is divided into distinct time periods which represent portions of the thermal process. Each zone is characterized by one or more measurements extracted from each zone (e.g., temperature, slope or time value).

2 APPLICABLE DOCUMENTS

2.1 IPC 1

IPC-T-50 Terms and Definitions for Interconnecting and Packaging Electronic Circuits

IPC-CA-821 General Requirements for Thermally Conductive Adhesives

IPC-2222 Sectional Design Standard for Rigid Organic Printed Boards

IPC-9501 PWB Assembly Process Simulation for Evaluation of Electronic Components

IPC-9502 PWB Assembly Soldering Process Guideline for Electronic Components

IPC-9504 Assembly Process Simulation for Evaluation of Non-IC Components (Preconditioning Non-IC Components)

2.2 Joint Industry Standard

J-STD-001 Requirements for Soldered Electrical and Electronic Assemblies

J-STD-002 Solderability Tests for Component Leads, Terminations, Lugs, Terminals and Wires

2.3 Other Industry Standard

JEP 140 Beaded Thermocouple Temperature Measurement of Semiconductor Packages

3 CONVECTION REFLOW PROFILING

3.1 Time/Temperature Profiles

The solder profile, also known as thermal profile, is one of the key variables in the manufacturing process that

IPC-7530A Draft Document for Industry Consensus Only August 2016 significantly impacts product yield, quality and reliability. Conveyor speed and panel temperatures are two variables in solder profile development. The solder profile is not only product specific; it is also flux and solder alloy dependent. Different pastes require different profiles for optimum performance, so it is important to consult the paste manufacturer before developing the solder profile.

For developing the profile, the loaded board is needed for which the profile is being developed. Start with a given belt speed and monitor the top-side board temperature using thermocouples. Most new reflow ovens have built-in thermocouples and software packages to record the thermal profile. Also, commercial hardware and software packages, such as MOLE, data pack and many others are available to make thermal profile development an easy task. Use of such profilers has been important in tin/lead assemblies. Not it is only important, but it is critical that such profilers be used on each product to achieve good yield without exceeding the temperature constraints imposed by different types of components. Table 3-1 provides key reflow profiles for both tin/lead and lead-free assemblies and also for mixed assemblies (backward and forward compatibility profiles). Note that profiles for lead-free and forward-compatibility are the same. Table 3-2 provides profiles for SAC and low temperature lead free alloys containing bismuth.

Table 3-1 Profile Comparison Between SnPb, SAC 305 and Mixed Alloys

Profile Topic SnPb Alloy Profile Mixed/Backward

Compatibility Profile

Alloy Solidus temperature

Target Alloy peak temp range

Absolute Minimum peak reflow temperature **

183 °C

210 °C to 220 °C

205 °C

183 °C/220 °C

228 °C to 232 °C

228 °C

Pb-Free Alloy (SAC

305)/Forward

Compatibility

Profile

217 °C to 220 °C

235 °C to 245 °C

230 °C

Component ramp up rate

Component ramp down rate

2 °C to 4 °C / second * 2 °C to 4 °C / second *

2 °C to 6 °C / second * 2 °C to 6 °C / second *

100 °C to 180 °C * 100 °C to 180 °C * Soak or preheat activation temperature

Soak or preheat activation time 60 to 120 seconds * 60 to 120 seconds *

2 °C to 4 °C / second *

2 °C to 6 °C / second *

140 °C to 220 °C *

60 to 150 seconds *

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

Dwell time above liquidus

Dwell time at peak temp.

60 to 90 seconds

20 seconds max

60 to 90 seconds

20 seconds min

60 to 90 seconds

20 seconds max

Solder Paste used

SMT Component Types

Tin-lead Paste Tin Lead Paste Lead Free (SAC 305) Paste

All SMT Type Tin-Lead and

Lead Free BUT NOT Lead

Free BGA Balls

All SMT Type Tin-Lead and

Lead Free INCLUDING SAC

Lead Free BGA Balls

ALL COMPONETS

INCLUDING BGAs are Lead

Free including BGAs with

SAC 305 Lead Free BGA balls

Reason for Peak Temperatures Lead Free surface finishes on BGA Parts have no problem melting at

2050C. Also all tin-lead surface finishes have 90% tin any way. Lead Free finishes have close to

100% tin with some other lead free elements like Bismuth

A compromise temperature is needed so that tin lead parts do not get overheated and lead free

SAC BGAs with melting point of 22 °C can melt, collapse and fully mix with tin-lead paste. Lower peak temperatures will cause

SAC BGA balls to either not melt or partially melt and increase the incidence of

HoP, Opens and poor reliability

All components are lead free and can take higher heat. However, too high a peak temperature may cause BGA ball drops, opens, dewetting and board warpage and Large

BGAs are tested for maximum of

245c for MSL level rating

* Verify with the supplier

** Coolest Temperature on the board

Table 3-2 Profile Comparison Between SAC Alloy, SnBi (Low-Temp) Alloys and Resin-Containing SnBi Solder

Pastes

Profile Topic

SAC 305 Solder Paste

SnBi Low Temperature

Solder Paste Profile

Profile

Resin Containing SnBi Low

Temperature

Alloy Solidus temperature 217 °C to 220 °C 139 °C to 140 °C 139 °C to 140 °C

Target Alloy peak temp range

Absolute Minimum peak reflow temperature **

Component ramp up rate

Component ramp down rate

Soak or preheat activation temperature

235 °C to 245 °C

230 °C

2 °C to 4 °C / second * 1 °C to 3°C / second *

2 °C to 6 °C / second * 2 °C to 6 °C / second *

140 °C to 220 °C *

160 °C to 200 °C

160 °C

100 °C to 120 °C *

160 °C to 180 °C

160 °C

2 °C to 4 °C / second *

2 °C to 6 °C / second *

None

Soak or preheat activation time 60 to 150 seconds * 30 to 90 seconds *

(to avoid premature curing

None

Dwell time above liquidus

Dwell time at peak temp.

Post Reflow Resin Cure Temp

Post Reflow Resin Cure Time

60 to 90 seconds

20 seconds max

N/A

30 to 90 seconds *

20 seconds max *

N/A

(to avoid premature curing

60 to 210 seconds *

Varies #

125 °C to 130 °C #

130 to 240 secs #

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

Solder Paste used

SMT Component Types

ALL COMPONETS

INCLUDING BGAs are Lead

Free including BGAs with

SAC 305 Lead Free BGA balls eutectic) Low temperature without resin

ALL COMPONETS

INCLUDING BGAs are Lead

Free including BGAs with

SAC 305 Lead Free BGA balls (Do NOT use BGAs with SnPb solder balls)

SnBi (eutectic or noneutectic) Low temperature

WITH resin

ALL COMPONETS

INCLUDING BGAs are Lead

Free including BGAs with

SAC 305 Lead Free BGA balls (Do NOT use BGAs with SnPb solder balls)

* Verify with the supplier

** Coolest Component on Board

# Some resin containing solder pastes require extended time after the reflow phase in the reflow profile to cure the

With tin/lead, there has been general consensus in the industry about the composition of solder to be used: eutectic solder with 63 % tin and 37 % lead composition with melting point of 183 °C. With this composition, there was a big difference between the melting point (183 °C) and peak temperature (220 °C). It provides a very wide window (35C) his is a very wide window and reflow profile development is much easier.

In lead-free assembly, the commonly used SAC (Sn, Ag and Cu) solders contain 3 % to 4% silver, 0.5 % to 0.7% copper and the rest tin. These alloys have a melting point around 220 °C. A few components, such as some aluminum electrolytic capacitors, put restrictions on maximum temperature and duration above 230 °C to which they can be subjected. Additional constraints will be dictated by low-cost laminates, plastic connectors and moisture-sensitive components if used.

To accommodate such constraints, the peak temperature in lead-free assemblies should be maintained between

230 °C and 245 °C, a variation of only 15 °C, which is a tight process window. This is about a 60 % drop from the 35

°C variation with tin/lead assemblies as mentioned earlier. The difficulty of achieving a reflow profile to meet the defined process window is further increased if large components with high thermal mass are used on the same board with smaller, temperature-sensitive components. The reasons are simple. The large components with high thermal mass require a larger heat input to meet the process window requirements for peak temperature and time above liquidus. However, this large heat input may result in smaller, temperature-sensitive components falling outside the process window requirements. To resolve this issue, very tight process control and narrow temperature bandwidth across the board are necessary. Many assembly houses may have a hard time meeting such requirements, especially on complex boards, without concerted time and effort in developing reflow profiles.

The problem can be further compounded by backward compatibility issues in which some lead-free components are used on a primarily tin/lead board. In such cases, the profile must accommodate both tin/lead and lead-free package requirements.

Figure 3-1 shows a schematic of a profile. Figure 3-2 shows a real-world example for a SnPb profile. Figure 3-3 shows an example of a SAC 305 profile for a single-sided board moving at 24 in/sec. Figure 3-4 is the same board but double-sided. Note almost the same oven temperature but a slower belt speed of 21 in/sec.

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

Figure 3-1 Schematic of Reflow Profile

Figure 3-2 SnPb Profile With Multiple Thermocouples

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

Figure 3-3 Example of a SAC 305 Profile for a Single-Sided Board (Speed is 24 in/sec)

Figure 3-4 Example of a SAC 305 Profile for a Double-Sided Board (Speed is 21 in/sec)

There are two major types of profiles – ramp to soak and then to peak or RSP (Figure 3-5 top) and ramp to peak or

RP (Figure 3-5 bottom). The key difference between them is absence of soak zone in RP profile. Use of soak zone in RSP profile allows more uniform temperature across the board is very useful in achieving uniform temperature in a board with large variation in thermal masses of different components on the board. RSP profiles also make it easier to achieve lower voids in solder joints especially in BGAs. Ramp to peak or RP profiles may increase incidence of voids in solder joint but they minimize incidence of head on pillow in BGAs. Head on pillow is a serious defect. Presence of voids, especially under IPC 610 specification limits, is not a serious concern for product

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.