IPC-9708 Explained: Complete Guide to PCB Pad Cratering Test Methods for BGA Reliability

Meta:Master IPC-9708 pad cratering test methods for lead-free BGA assembly. Learn pin pull, ball pull, ball shear testing & how to establish pass/fail criteria.

The first time I saw pad cratering on a production board, I thought we had a solder joint failure. The BGA came off cleanly during rework, and I assumed the joint had cracked. But when I looked at the PCB, I saw something that made my stomach drop—the copper pads had torn right out of the laminate, leaving craters where they used to be.

That board passed electrical test. It passed X-ray inspection. It would have shipped to the customer and failed in the field, and we never would have known why until the warranty returns started piling up.

Pad cratering became one of the most frustrating failure modes in lead-free assembly precisely because it’s so hard to detect. IPC-9708 gives us standardized methods to characterize and compare PCB materials for their resistance to this insidious defect.

What Is IPC-9708?

IPC-9708, officially titled “Test Methods for Characterization of Printed Board Assembly Pad Cratering,” was released in December 2010. The standard provides three distinct test methods to evaluate how susceptible PCB assemblies are to pad cratering failures.

Unlike many IPC standards, IPC-9708 explicitly states that it provides test methods only—no acceptance criteria or pass/fail limits are defined. This is intentional because pad cratering susceptibility varies dramatically based on application requirements, and the standard’s authors recognized that one-size-fits-all limits wouldn’t work.

Understanding Pad Cratering: The Hidden Killer

Pad cratering is fundamentally different from solder joint cracking, though both can cause electrical opens. In pad cratering, the failure occurs within the PCB laminate itself—specifically in the prepreg layer underneath the copper pad.

How Pad Cratering Differs from Solder Failure

When pad cratering occurs, the copper pad separates from the PCB along with a chunk of the underlying dielectric material. The pad typically stays attached to the BGA component, leaving a visible crater on the board surface. The critical issue is that partial cratering—where cracks have initiated but not propagated completely—often passes electrical testing and only fails later under field stress.

Why Lead-Free Assembly Made Pad Cratering Worse

Pad cratering existed before lead-free, but it was relatively rare. The transition to RoHS-compliant assembly changed several factors simultaneously, all of which increased pad cratering risk:

The combination of stiffer solder alloys transmitting more stress through joints that were already under higher residual stress from elevated reflow temperatures, attached to more brittle laminate materials, created a perfect storm for pad cratering.

The Three IPC-9708 Test Methods

IPC-9708 defines three distinct approaches to characterizing pad cratering susceptibility. Each has advantages and limitations, and the choice depends on your specific evaluation needs.

Pin Pull Test Method

The pin pull test is considered the most sensitive method for evaluating board material and design variables. In this test, a metal pin is soldered to the pad and then pulled perpendicular to the board surface until fracture occurs.

The pin pull test can be performed “hot” (at elevated temperature, typically up to 180°C) or “cold” (room temperature). Hot testing may better simulate certain stress conditions but requires specialized fixturing to maintain temperature during the pull.

Key Advantage: The pin pull test achieves the highest percentage of laminate cracking failures (>90%), meaning it most consistently reveals the true pad cratering resistance of the material rather than failing in the solder.

Key Limitation: Requires soldering pins to pads, which adds sample preparation time and introduces variables from the soldering process itself.

Ball Pull Test Method

The ball pull test is specifically designed for BGA components. After BGA attachment (or ball attach to test coupons), a specialized gripper grasps the solder ball and pulls it perpendicular to the board.

The ball pull test is more convenient than pin pull because it can be performed directly on assembled boards or ball-attached test vehicles without additional soldering operations.

Key Advantage: Quick testing after BGA ball attach with no additional preparation needed.

Key Limitation: Results are highly dependent on solder ball formation quality and process control. Variability in the solder joint can mask differences in laminate properties.

Ball Shear Test Method

The ball shear test is the most commonly used method due to its convenience. A shear tool applies lateral force to the solder ball, pushing it parallel to the board surface until failure.

The ball shear test is popular because it uses widely available equipment and requires minimal sample preparation. However, it has a significant limitation.

Key Advantage: Most convenient to execute, fastest throughput, uses standard bond tester equipment.

Key Limitation: Failure mode is inconsistent—approximately 50% of failures occur in the solder rather than the laminate, which means you may not be measuring pad cratering resistance at all. This can lead to misleading comparisons between materials.

Comparing the Three Methods

For comprehensive material evaluation, many engineers run all three tests to get a complete picture. For routine screening, ball shear provides the fastest results but with lower confidence in pad cratering specificity.

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

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

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IPC-9708 Test Equipment and Setup Requirements

Implementing IPC-9708 testing requires appropriate equipment and careful attention to test parameters.

Required Equipment

Critical Test Parameters

Several parameters significantly affect test results and must be controlled:

Shear/Pull Height: For ball shear testing, the height of the shear tool above the pad surface affects whether the failure occurs in the solder or laminate. Lower heights increase the likelihood of pad cratering failure modes.

Test Speed: Higher speeds tend to produce more brittle failure modes. IPC-9708 allows variable speeds, but consistency within a test program is essential for valid comparisons.

Temperature: Testing at elevated temperature generally reduces apparent strength but may better represent actual use conditions. Document and control temperature for all tests.

Establishing Pass/Fail Criteria for IPC-9708

Here’s where IPC-9708 frustrates many engineers: the standard explicitly states that acceptance criteria must be established by agreement between user and supplier (AABUS). There are no universal pass/fail limits.

Why No Standard Limits?

The absence of defined limits is intentional:

How to Establish Your Own Criteria

To develop meaningful pass/fail criteria for your application:

Step 1: Baseline Testing – Test your current production materials and designs that have acceptable field reliability. This establishes your performance baseline.

Step 2: Define Failure Modes – Determine what percentage of pad cratering failures (vs. solder failures) is acceptable for valid testing.

Step 3: Statistical Analysis – Run sufficient samples to establish mean values and standard deviations. Typical sample sizes are 30-50 pulls/shears per test condition.

Step 4: Set Limits – Based on baseline data and required safety margin, establish minimum acceptable force values and maximum acceptable pad cratering percentage.

Step 5: Correlation – If possible, correlate your test results with board-level reliability testing (thermal cycling, drop test) to validate that your limits predict actual field performance.

Pad Cratering Detection Challenges

One of the most frustrating aspects of pad cratering is how difficult it is to detect before catastrophic failure.

Why Standard Inspections Miss Pad Cratering

Partial pad cratering—where cracks have initiated but not propagated to cause electrical failure—is essentially invisible to standard production testing. This creates latent defects that escape to the field.

Advanced Detection Methods

For critical applications, additional detection methods may be justified:

Acoustic Emission Monitoring: Sensors detect the acoustic signature of crack formation during mechanical testing. Research has shown this can identify pad cratering initiation before electrical failure occurs.

Dye Penetration Testing: After assembly or stress testing, dye is applied and allowed to penetrate any cracks. Subsequent component removal reveals the extent of cratering through dye staining.

IPC-9708 Mitigation Strategies for Pad Cratering

When testing reveals pad cratering susceptibility, several mitigation options exist:

Solder mask defined (SMD) pads generally show better pad cratering resistance than non-solder mask defined (NSMD) pads because the solder mask provides additional contact area between the copper and laminate, distributing stress over a larger region.

IPC-9708 vs Related Standards

Understanding how IPC-9708 relates to other reliability standards helps build a comprehensive test program.

IPC/JEDEC-9702 (monotonic bend testing) can induce pad cratering during board flexure, but it tests the complete assembly response rather than specifically characterizing pad cratering resistance. IPC-9708 provides focused pad-level testing that complements board-level methods.

Useful Resources for IPC-9708 Implementation

Official Standard Downloads

Related IPC Standards

Equipment Suppliers

Frequently Asked Questions About IPC-9708

Which IPC-9708 test method should I use?

It depends on your goals. For comprehensive material qualification, use all three methods—pin pull provides the highest pad cratering specificity, ball pull evaluates the actual assembly configuration, and ball shear offers the fastest throughput. For routine incoming inspection or screening, ball shear is most practical despite its lower sensitivity. For critical applications where pad cratering has caused field failures, prioritize pin pull testing for its >90% laminate failure rate.

Why doesn’t IPC-9708 include pass/fail criteria?

The standard’s authors recognized that appropriate limits vary dramatically by application. A consumer electronics product might tolerate lower pad strength than an automotive ECU or aerospace system. Additionally, pad cratering resistance depends on specific material combinations, pad designs, and assembly processes that vary between manufacturers. Imposing universal limits would either be too restrictive for some applications or insufficiently protective for others.

Can pad cratering occur with tin-lead solder?

Yes, but it’s much less common. Tin-lead solder is more compliant than SAC alloys, so it absorbs more strain energy rather than transmitting it to the pad interface. The lower reflow temperatures also create less residual stress. However, if you use high-Tg brittle laminates with tin-lead solder (sometimes done for reliability reasons), pad cratering can still occur under mechanical shock or excessive board flexure.

How do SMD pads reduce pad cratering compared to NSMD?

Solder mask defined (SMD) pads have solder mask overlapping the outer edge of the copper pad, creating a larger bonded area between the copper and laminate. This distributes stress over a wider region during mechanical loading. NSMD pads have the copper exposed beyond the solder mask opening, concentrating stress at the smaller copper-laminate interface. Studies show SMD pads can improve pad cratering resistance significantly, though they may affect solder joint reliability in other ways.

How does IPC-9708 testing correlate with field reliability?

Direct correlation is challenging because field failures depend on many variables beyond pad strength—shock exposure, thermal cycling, vibration, and handling damage all contribute. However, materials and designs that show higher pad pull/shear forces in IPC-9708 testing generally demonstrate better resistance to pad cratering in board-level drop and shock testing. Establishing correlation for your specific product requires testing both pad-level (IPC-9708) and board-level (drop, thermal cycle) specimens and comparing failure modes.

Final Thoughts

Pad cratering remains one of the most challenging failure modes in modern PCB assembly. It escapes standard inspection methods, creates latent defects that fail in the field, and became dramatically more common with the industry transition to lead-free soldering.

IPC-9708 gives us the tools to characterize and compare materials and designs for pad cratering susceptibility. While the lack of defined pass/fail criteria frustrates some engineers, it reflects the reality that appropriate limits depend on your specific application, materials, and reliability requirements.

The key is to baseline your current production—materials and processes you know work—and use IPC-9708 testing to evaluate any changes before they reach production. When pad cratering does occur, these same test methods help diagnose the root cause and validate corrective actions.

Your BGA solder joints are only as reliable as the pads they’re attached to. IPC-9708 helps ensure those pads stay put.