IPC-TP-1115 Explained: Selecting and Implementing No-Clean Flux Processes

The shift to no-clean soldering changed electronics manufacturing fundamentally. Eliminating the post-solder cleaning step promised faster throughput, lower costs, and reduced environmental impact from cleaning solvents. But making no-clean work reliably isn’t as simple as switching flux types and skipping the wash cycle. There’s real engineering involved in selecting the right materials and optimizing processes to ensure residues truly remain benign.

IPC-TP-1115, titled “Selection and Implementation Strategy for a Low-Residue No-Clean Process,” addresses exactly this challenge. Published in 1998 as the electronics industry was rapidly adopting no-clean processes, this technical paper provides a systematic framework for evaluating, selecting, and implementing no-clean flux systems. While it’s a relatively short document at 14 pages, IPC-TP-1115 packs substantial guidance for anyone transitioning to or optimizing no-clean assembly processes.

In this guide, I’ll walk through what IPC-TP-1115 covers, why proper no-clean implementation matters more than ever with today’s dense assemblies, and how to apply its principles to modern manufacturing challenges.

What Is IPC-TP-1115?

IPC-TP-1115 is a technical paper that provides guidance for selecting and implementing low-residue no-clean soldering processes in electronics assembly. Unlike specification documents that define requirements, IPC-TP-1115 offers strategic and practical guidance for the transition from traditional cleaned processes to no-clean manufacturing.

The document addresses a fundamental question that every process engineer faces when considering no-clean: how do you ensure that eliminating the cleaning step doesn’t compromise product reliability? IPC-TP-1115 provides a framework for answering that question systematically rather than through trial and error.

The “TP” designation indicates this is a Technical Paper rather than a formal standard or specification. Technical papers in the IPC system provide educational content, best practices, and implementation guidance that supports the application of formal standards.

Understanding No-Clean Soldering Fundamentals

Before diving into IPC-TP-1115’s guidance, it helps to understand what “no-clean” actually means and why proper implementation requires careful attention.

What Makes Flux “No-Clean”?

No-clean flux is formulated to leave minimal residue after soldering, with that residue designed to be electrically inert, non-corrosive, and non-hygroscopic under normal operating conditions. The key word is “designed”—achieving truly benign residues depends on proper process execution, not just material selection.

Traditional rosin-based and water-soluble fluxes require cleaning because their residues remain active and can cause corrosion, dendritic growth, or electrical leakage if left on assemblies. No-clean fluxes use different chemistry—typically low-solids formulations with mild organic acids that decompose or encapsulate during the soldering thermal cycle.

*Under proper process conditions and for appropriate applications

The Critical Role of Thermal Processing

Here’s what IPC-TP-1115 emphasizes and what many engineers underestimate: no-clean flux performance depends heavily on thermal processing. The flux must experience adequate heat for sufficient time to drive off volatiles and convert active components to their benign state.

When flux doesn’t fully process—due to insufficient peak temperature, inadequate time above liquidus, or shadowing effects—residues can remain active. These under-processed residues may cause the same reliability problems that cleaning was meant to prevent.

Key Topics Covered in IPC-TP-1115

IPC-TP-1115 addresses no-clean implementation through several interconnected topics. Understanding this structure helps you apply the guidance effectively.

Material Selection Criteria

The document provides criteria for evaluating and selecting no-clean flux materials. This includes flux classification considerations per J-STD-004, residue characteristics and their measurement, compatibility with PCB surface finishes, and performance across different soldering processes (wave, reflow, selective).

Material selection isn’t just about finding a flux that works in the lab—it’s about finding one that works reliably across the range of conditions your production will encounter.

Process Window Definition

IPC-TP-1115 addresses the importance of defining and maintaining process windows that ensure complete flux processing. This covers reflow profile requirements for residue deactivation, wave soldering parameters affecting residue formation, and the relationship between process parameters and residue characteristics.

A flux that performs well with one thermal profile may leave problematic residues with another. The document emphasizes characterizing this relationship before committing to production.

Qualification Testing

The technical paper provides guidance on testing approaches to validate no-clean implementation. This includes surface insulation resistance (SIR) testing, ionic contamination measurement, visual inspection criteria, and accelerated aging and environmental testing.

Implementation Strategy

Beyond material and process selection, IPC-TP-1115 addresses the organizational and procedural aspects of transitioning to no-clean, including pilot production approaches, process monitoring requirements, and criteria for ongoing verification.

No-Clean Flux Selection Per IPC-TP-1115 Principles

Selecting the right no-clean flux requires balancing multiple factors. IPC-TP-1115’s framework helps organize this evaluation.

Flux Classification and Activity Level

J-STD-004 classifies fluxes by composition and activity level. For no-clean applications, the relevant categories are typically ROL (rosin, low activity) and ORL (organic, low activity) with designations 0 or 1.

Lower activity fluxes leave less residue and pose lower reliability risk, but they also provide less cleaning action during soldering. The selection must balance residue concerns against solderability requirements.

Solderability Considerations

No-clean flux selection is directly tied to the solderability of your components and PCBs. With water-soluble flux, you can use high activity to overcome oxidation, then clean away the residue. With no-clean, the residue stays—so you need either better incoming solderability or careful activity level selection.

IPC-TP-1115 emphasizes that no-clean processes have less tolerance for solderability variation than cleaned processes. Incoming material quality becomes more critical.

Residue Characteristics

Different no-clean fluxes leave different residue characteristics. Some leave nearly invisible residues; others leave visible but benign films. The selection should consider cosmetic requirements, inspection implications, and conformal coating compatibility.

Implementing No-Clean Processes Successfully

IPC-TP-1115 provides strategic guidance for implementation that goes beyond just selecting materials.

Process Characterization

Before production implementation, characterize how your selected flux performs across your process window. This means profiling with thermocouples to ensure adequate flux processing, testing residue characteristics at process extremes, and evaluating performance across your product mix.

The goal is understanding where your process margins are, not just confirming that nominal conditions work.

Reflow Profile Optimization for No-Clean

Reflow profiles for no-clean flux often differ from those optimized purely for solder joint formation. No-clean profiles typically need adequate preheat for flux activation and volatile release, sufficient time above liquidus for complete flux processing, and controlled cooling to avoid residue cracking or whitening.

Wave Soldering Considerations

No-clean wave soldering presents additional challenges. Flux application must be controlled to avoid excess residue, preheat must be adequate for flux processing before wave contact, and the solder wave temperature and contact time affect residue characteristics.

IPC-TP-1115 addresses the specific considerations for wave soldering with no-clean flux, where residue management is often more challenging than in reflow processes.

Handling Low-Standoff Components

Modern assemblies with QFNs, LGAs, and other bottom-termination components present a challenge for no-clean processes. Flux trapped under low-standoff components may not fully process due to limited heat exposure and restricted outgassing paths.

For assemblies with significant low-standoff populations, IPC-TP-1115 principles suggest more conservative flux selection or consideration of cleaning even with no-clean flux.

When “No-Clean” Still Requires Cleaning

One of the most valuable aspects of IPC-TP-1115’s guidance is acknowledging that “no-clean” doesn’t mean “never clean.” Several situations warrant cleaning even when using no-clean flux.

High-Reliability Applications

For aerospace, military, medical implants, and other high-reliability applications, the risk tolerance for flux residue is much lower. Even properly processed no-clean residue represents a potential failure mode that cleaning eliminates.

Conformal Coating Application

Conformal coatings may not adhere properly to flux residue, or residue may cause coating defects. Even no-clean residue can interfere with coating adhesion, cause fish-eyes or dewetting, and trap moisture between residue and coating.

Many conformal coating specifications require cleaning before coating regardless of flux type.

Testing and Probe Contact

Flux residue can interfere with electrical testing by preventing reliable probe contact. In-circuit test and flying probe systems may require cleaning to ensure test reliability, particularly for fine-pitch devices.

Process Deviations

When process conditions fall outside the characterized window—such as underheated assemblies, excessive flux application, or extended time between print and reflow—cleaning may be necessary to ensure residue is rendered harmless.

Read more IPC Standards:

MIL-PRF-38534: Hybrid Microcircuits Military Specification Guide for Engineers

MIL-PRF-31032: The Definitive Guide to Military-Grade PCB Requirements

MIL-PRF-19500: Military Semiconductor Device Specification Explained

MIL-PRF-123: High-Reliability Ceramic Capacitor Military Standard

MIL-I-46058CMIL-I-46058C: Military Conformal Coating Specification Complete Guide

MIL-HDBK-263: ESD Control Handbook & Implementation Guide

J-STD-075 Guide: PSL Classification for Passive Components & Assembly Process Limits

J-STD-035 Guide: Acoustic Microscopy for IC Package Inspection & Defect Detection

J-STD-033 Guide: MSD Handling, Floor Life, Baking & Dry Storage Requirements

J-STD-032 Explained: Ball Grid Array Ball Construction & Performance Specs

J-STD-027 Guide: Mechanical Outline Standard for Flip Chip & CSP Packages

J-STD-020 Guide: MSL Classification, Reflow Profiles & Moisture Sensitivity Testing

IPC/WHMA-A-620 Explained: Complete Guide to Cable & Wire Harness Standards

IPC-SG-141: Complete Guide to S-Glass Fabric Specifications for PCB Laminates

IPC-QF-143: Complete Guide to Quartz Fabric Specifications for RF/Microwave PCB Laminates

Reliability Testing for No-Clean Processes

IPC-TP-1115 emphasizes the importance of reliability testing to validate no-clean implementation. Testing verifies that your specific combination of materials, processes, and products will perform reliably.

Surface Insulation Resistance Testing

SIR testing measures the electrical resistance between conductors under temperature and humidity stress. This is the primary method for evaluating whether flux residue poses reliability risk.

Ionic Contamination Testing

Ionic contamination measurement (ROSE testing or ion chromatography) quantifies the amount of ionic material on assembly surfaces. While not a direct reliability predictor, ionic contamination levels indicate whether flux residue might pose risk.

Electrochemical Migration Testing

For fine-pitch assemblies, electrochemical migration (ECM) testing evaluates the tendency for conductive paths to form between conductors under bias and humidity. This directly addresses a failure mode that flux residue can enable.

IPC-TP-1115 and Related Standards

IPC-TP-1115 works within a broader framework of IPC and joint industry standards. Understanding these relationships helps apply the guidance effectively.

IPC-TP-1115 provides implementation strategy; these related standards provide specifications and test methods that support implementation.

Practical Tips for No-Clean Implementation

Based on IPC-TP-1115 principles and industry experience, here are practical recommendations for successful no-clean implementation.

Start with Good Incoming Quality

No-clean processes have less margin for poor solderability. Establish and enforce incoming quality requirements for component solderability, PCB surface finish condition, and solder paste shelf life management.

Characterize Before Committing

Before full production implementation, run comprehensive characterization including process window studies, multiple lots of materials, and reliability testing under worst-case process conditions.

Monitor Continuously

No-clean processes require ongoing attention. Establish monitoring for flux application consistency, thermal profile verification, visual residue inspection, and periodic SIR or ionic testing.

Don’t Assume—Verify

The “no-clean” label doesn’t guarantee reliable residue. Verify through testing that your specific process produces benign residue for your specific application requirements.

Who Needs IPC-TP-1115?

IPC-TP-1115 provides value for several roles in electronics manufacturing.

For organizations transitioning from cleaned to no-clean processes, or optimizing existing no-clean operations, IPC-TP-1115 provides foundational guidance that remains relevant despite the document’s age.

Where to Get IPC-TP-1115

IPC-TP-1115 is available through IPC and authorized distributors.

Related Documents to Consider

For comprehensive no-clean process implementation, consider obtaining these complementary documents.

The Ongoing Relevance of No-Clean Process Guidance

While IPC-TP-1115 was published in 1998, its principles remain highly relevant. If anything, proper no-clean implementation has become more critical as assemblies have become denser and component standoffs have decreased.

An estimated 80% of SMT assembly worldwide now uses no-clean processes. Yet flux residue continues to cause field failures, particularly in high-reliability applications and harsh environments. The systematic approach IPC-TP-1115 advocates—careful selection, thorough characterization, and ongoing verification—addresses these continuing challenges.

Modern considerations like lead-free soldering (requiring higher reflow temperatures that generally improve flux processing) and fine-pitch components (creating residue management challenges) build on rather than replace IPC-TP-1115’s fundamental guidance.

Frequently Asked Questions About IPC-TP-1115

What is the main purpose of IPC-TP-1115?

IPC-TP-1115 provides strategic and practical guidance for selecting and implementing no-clean soldering processes in electronics assembly. It helps process engineers understand how to evaluate no-clean flux options, establish appropriate process parameters, and verify that their implementation produces reliable assemblies without post-solder cleaning.

Is IPC-TP-1115 still relevant given its 1998 publication date?

Yes, IPC-TP-1115 remains relevant because the fundamental principles of no-clean process implementation haven’t changed. The physics of flux processing, the reliability concerns with residue, and the systematic approach to implementation apply regardless of specific flux chemistries or component technologies. Modern challenges like lead-free soldering and fine-pitch components build on rather than invalidate this foundational guidance.

Does IPC-TP-1115 say you never need to clean with no-clean flux?

No, IPC-TP-1115 acknowledges that “no-clean” doesn’t mean “never clean.” The document recognizes situations where cleaning remains appropriate even with no-clean flux, including high-reliability applications, conformal coating preparation, and cases where process conditions may not fully process flux residue. The guidance helps determine when cleaning adds value despite using no-clean materials.

How does IPC-TP-1115 relate to J-STD-004 flux classification?

IPC-TP-1115 references the J-STD-004 flux classification system as the basis for flux selection. J-STD-004 defines flux categories (rosin, organic, inorganic) and activity levels (L0, L1, M, H) that IPC-TP-1115 uses when discussing selection criteria. Understanding J-STD-004 classifications helps apply IPC-TP-1115’s selection guidance effectively.

What testing does IPC-TP-1115 recommend for validating no-clean processes?

IPC-TP-1115 emphasizes reliability testing to validate no-clean implementation, particularly surface insulation resistance (SIR) testing under temperature and humidity stress. The document also addresses ionic contamination measurement, visual inspection criteria, and accelerated aging tests. These tests verify that the specific combination of materials and process parameters produces benign residue for the intended application.

Building Reliable No-Clean Processes

IPC-TP-1115 represents accumulated industry knowledge about making no-clean processes work reliably. The document’s systematic approach—understanding materials, characterizing processes, testing thoroughly, and monitoring continuously—provides a framework that applies regardless of specific flux products or assembly technologies.

For process engineers implementing or optimizing no-clean assembly, IPC-TP-1115 offers guidance that can prevent reliability problems before they reach the field. The modest investment in this technical paper can save significant troubleshooting effort and, more importantly, prevent field failures that damage customer relationships and product reputation.

No-clean soldering works extremely well when implemented properly. IPC-TP-1115 helps define what “properly” means for your specific application.