Crane Division, Naval Surface Warfare Center Lead Free

Pb Crane Division, Naval Surface Warfare CenterLead Free LEAP-WG10 April 2008 Distribution Statement A: Approved for Public Release; distribution is unlimited

Presenter Gary S Latta 2M Program 812-854-1973 E-mail: gary.latta@navy.mil Crane Division, Naval Surface Warfare Center

Lead-Free Control Plan

What it is N S W C C r a n e L e a d F r e e C o n t r o l P l a n • A Risk Management tool • A Pb-free policy document • Identifies what can/cannot be done • An education tool • An implementing document

What it is not N S W C C r a n e L e a d F r e e C o n t r o l P l a n • A 100% solution • “The” answer to Pb-free

Structure N S W C C r a n e L e a d F r e e C o n t r o l P l a n 1. SCOPE 2. REFERENCES 3. TERMS AND DEFINITIONS 4. SYMBOLS AND ABBREVIATED TERMS 5. OBJECTIVES 6. TECHNICAL REQUIREMENTS 7. ADMINISTRATIVE REQUIREMENTS

Structure N S W C C r a n e L e a d F r e e C o n t r o l P l a n 0. BACKGROUND 1. SCOPE 2. REFERENCES 3. TERMS AND DEFINITIONS 4. SYMBOLS AND ABBREVIATED TERMS 5. OBJECTIVES 6. TECHNICAL REQUIREMENTS 7. ADMINISTRATIVE REQUIREMENTS

0. Background N S W C C r a n e L e a d F r e e C o n t r o l P l a n • RoHS and other mandates • Commercial market impact on military electronics • Increased reliability risks • No drop in replacement for SnPb solder

0. Background N S W C C r a n e L e a d F r e e C o n t r o l P l a n • For over fifty years, the electronics industry has relied on tin-lead (SnPb) solder as the primary means of interconnection between electronic devices. The reliability of SnPb interconnections is well known, well studied, and well documented. The European Union’s (EU) Restriction of Hazardous Substances[1] (RoHS) directive and other international and domestic mandates to eliminate materials deemed hazardous has forced the electronics industry to adopt solders free of lead (Pb). While military electronics have received exclusions from these Pb-free imperatives, the reality is that the consumer marketplace drives the electronic industry, not the military. To remain competitive electronics companies and their suppliers worldwide must change to solders and materials compatible with Pb-free assembly. Electronics for high reliability applications, such as the military, rely heavily on commercial components, and, in some cases, circuit boards, assemblies, and equipment, the majority of which have been or will be transitioned to Pb-free. Based on the scientific information available today, there are increased reliability risks due to the implementation of Pb-free into military electronics. These risks are the spontaneous formation of tin whiskers from pure tin (Sn) finishes, reduced Pb-free solder joint reliability, limited rework opportunities from copper dissolution, cross-contamination between the different alloys, and the potential damage from higher Pb-free processing temperatures. Because there is no drop-in replacement for SnPb solder, the conversion of the commercial supply chain to Pb-free components, circuit boards, and assemblies requires due diligence to ensure that the reliability of military electronics is maintained and not adversely impacted from the unwitting introduction of Pb-free. This Lead Free Control Plan (LFCP) for the Crane Division, Naval Surface Warfare Center (NSWC Crane) provides such due diligence. [1] Sometimes referred to as Reduction of Hazardous Substances (RoHS)

1. Scope N S W C C r a n e L e a d F r e e C o n t r o l P l a n • Policies, processes, documentation • Inherent risks to Pb-free • Risk management processes • Implementation of Pb-free is limited • Other Pb-free uses are prohibited

1. Scope N S W C C r a n e L e a d F r e e C o n t r o l P l a n • This LFCP describes the policies, authorized soldering processes, and reference documents NSWC Crane uses to ensure that its deliverable electronic products will satisfy the applicable requirements for performance, reliability, safety, and certifiability throughout the lifecycle as the global electronics industry transitions to Pb-free. This LFCP addresses the inherent risks with Pb-free, defines the limited acceptable uses of Pb-free, and provides risk management processes relating to new product build, rework, repair, component acquisition, and commercial-off-the-shelf (COTS) procurement, as well as the flow-down of these processes and requirements to all lower-tier suppliers. • All electronic assemblies, equipment, and systems supplied by NSWC Crane shall meet the reliability and product lifecycle requirements of the applicable program specification. Introduction of Pb-free is limited to the authorized soldering processes (SnPb, 1, 2, 3, or 4) described below in paragraph 6.2.3. This LFCP prohibits uses of Pb-free solders for assembly, rework, and repair unless there is sufficient documented data to indicate continued reliable performance as defined by the program specification. For COTS procurements where Pb-free is likely to be unavoidable, processes 5 and 5a in paragraph 6.2.3. apply. • This LFCP is a baseline document in that it describes policies, authorized processes, and reference documents that are common to most NSWC Crane products and programs. Some applications may have unique requirements that exceed the scope of this baseline LFCP. In those cases, modifications will be negotiated with the customer and formally documented as an addendum to this LFCP.

1.1 Exclusions N S W C C r a n e L e a d F r e e C o n t r o l P l a n • Specialized solder alloys • Non-tactical equipment • COTS NOT excluded when in critical applications

1.1 Exclusions N S W C C r a n e L e a d F r e e C o n t r o l P l a n • This LFCP does not preclude the use of specialized solder alloys other than Sn37Pb eutectic solder required for high operating temperature, low temperature step soldering, RF applications, etc. as required by program specification. • This LFCP excludes commercial non-tactical equipment, such as oscilloscopes, cameras, and personal computers etc., that support ongoing work activities in non-critical environments. This exclusion does not apply to any commercial equipment used in mission critical systems and/or safety of flight circumstances.

Inclusions/Exclusions N S W C C r a n e L e a d F r e e C o n t r o l P l a n Non-Tactical Equipment MissionCriticalSafety ofFlight

2. References N S W C C r a n e L e a d F r e e C o n t r o l P l a n • NAVSURFWARCENDIVCRANEINST 4855.10 • NAVSURFWARCENDIVCRANEINST 4855.18B • IPC-A-610 • J-STD-001 • IPC-7711/7721 • NAVAIR 01-1A-23NAVSEA SE004-AK-TRS-010/2M

2. References N S W C C r a n e L e a d F r e e C o n t r o l P l a n • J-STD-609 • GEIA-STD-0005-2 • GEIA-STD-0005-3 • GEIA-STD-0006-1

3. Terms and Definitions N S W C C r a n e L e a d F r e e C o n t r o l P l a n • IPC T-50

4. Symbols and Abbreviated Terms N S W C C r a n e L e a d F r e e C o n t r o l P l a n • HSD – hot solder dip • Pb – lead • Sn – tin • Sn37Pb – 63% tin 37% lead eutectic solder

5. Objectives N S W C C r a n e L e a d F r e e C o n t r o l P l a n • To meet the reliability and product lifecycle requirements of the specific program specification and produce high reliability military (Class III) electronic products • To maintain control of the configurations of all systems, equipment, assemblies, and sub-assemblies, as required by the specific program • To avoid, transfer, or mitigate the increased risks factors for military high-reliability electronics that the global transition to Pb-free has introduced

5. Objectives N S W C C r a n e L e a d F r e e C o n t r o l P l a n • To introduce no additional limitations of use for the electronic assemblies bought, built, reworked, or repaired in accordance with this LFCP • To require the repair, maintenance, and support activities under NSWC Crane comply with this LFCP • To apply the requirements of this LFCP to any outsourced products procured by NSWC Crane, except as excluded in paragraph 1.1

5. Objectives N S W C C r a n e L e a d F r e e C o n t r o l P l a n • To meet the reliability and product lifecycle requirements of the specific program specification and produce high reliability military (Class III[1]) electronic products • To maintain control of the configurations of all systems, equipment, assemblies, and sub-assemblies, as required by the specific program • To avoid, transfer, or mitigate the increased risks factors for military high-reliability electronics that the global transition to Pb-free has introduced • To introduce no additional limitations of use for the electronic assemblies bought, built, reworked, or repaired in accordance with this LFCP • To require the repair, maintenance, and support activities under NSWC Crane comply with this LFCP • To apply the requirements of this LFCP to any outsourced products procured by NSWC Crane, except as excluded in paragraph 1.1 • [1] Per J-STD-001 and IPC-A-610.

6. Technical Requirements N S W C C r a n e L e a d F r e e C o n t r o l P l a n • 6.1 Risks and Limitations of Use • 6.2 Risk Management • 6.3 Reliability • 6.4 Processes and Materials • 6.5 Configuration Control and Product Identification • 6.6 Aircraft Wiring

6.1 Risks and Limitations of Use N S W C C r a n e L e a d F r e e C o n t r o l P l a n • 6.1.1 Tin whiskers • 6.1.2 Solder joint reliability • 6.1.3 Copper dissolution • 6.1.4 Cross-contamination • 6.1.5 Processing temperatures

6.1 Risks and Limitations of Use N S W C C r a n e L e a d F r e e C o n t r o l P l a n • The transition to Pb-free in military high-reliability electronics has introduced a number of increased risk factors; including: • Tin Whiskers—Pure Sn finishes have a propensity to whisker • Solder Joint Reliability—Largely unknown for Pb-free used in military environments • Copper Dissolution—Limits rework and repair opportunities • Cross-Contamination—The reliability impact of mixing Pb-free alloys with other Pb-free alloys and/or SnPb is largely unknown • Higher Processing Temperatures—Greater potential for damage to the circuit boards and/or components can exist • The authorized soldering processes (SnPb, 1, 2, 3, or 4) identified in paragraph 6.2.3. avoid these risk factors except for in some cases tin whiskers, which require mitigation per GEIA-STD-0005-2. For COTS bought per processes (5 or 5a), these risk factors must be accepted except for tin whiskers, which can be mitigated per GEIA-STD-0005-2. • The authorized soldering processes (SnPb, 1, 2, 3, or 4) defined in paragraph 6.2.3. introduce no additional limitations of use for the electronic assemblies bought, built, reworked, or repaired in accordance with this LFCP. For COTS bought per processes (5 or 5a), no such assertion is made.

6.1.1 Tin Whiskers N S W C C r a n e L e a d F r e e C o n t r o l P l a n • Electrically conductive, crystalline structures • Can grow to lengths of several millimeters

6.1.1 Tin Whiskers N S W C C r a n e L e a d F r e e C o n t r o l P l a n • Tin whiskers are pure tin crystal conductive filaments which can result in pin to pin or pin to trace shorting. The formation of tin whiskers is a means of stress relief of compressive forces within the tin. Contributing conditions are known, but not well understood. The exact event or sequence of events that result in the start of a tin whisker is being researched. Driven by the transition to Pb-free products, tin whiskers pose major safety, reliability, and potential liability threats to all makers and users of high reliability electronics and associated hardware. Hardware manufacturers do not have many options. The primary means of mitigation are component termination retinning and conformal coating. Retinning is required when addressing safety of flight where loss of aircraft or injury to flight crew may exist. Retinning brings with it the possible introduction of latent component defects as well as the associated increased material costs. Determination of the risk is established through a platform risk analysis. All conformal coating will likely require a change to existing processes. The appropriate selection of conformal coating may also change. Issues of rework or method of application are driving factors that must likewise be addressed. None of the existing approaches are totally sufficient to control tin whiskering in high-reliability systems.

6.1.2 Solder Joint Reliability N S W C C r a n e L e a d F r e e C o n t r o l P l a n • Little long-term field reliability data on LF in military environments • Reliability of solder joint indications • LF more than SnPb in low stress conditions • LF less than SnPb in high stress conditions

6.1.2 Solder Joint Reliability N S W C C r a n e L e a d F r e e C o n t r o l P l a n • Insufficient data exist to validate whether Pb-free solder is reliable enough to sustain military hardware through the lifecycle of the system. The existing data from controlled studies indicates that Pb-free solder typically outperforms Sn37Pb solder under low stress conditions (For example for SAC305 was able to out perform SnPb with stress level below 5% of the ultimate strength) and SnPb solder outperforms Pb-free solder under higher stress conditions. With no drop-in replacement for Sn37Pb solder, a multitude of alternative Pb-free alloys are available. The general trend of the commercial industry has been SAC305. Due to the demand for higher mechanical shock/vibration performance SAC105 is now being considered. A low level of indium (In) is also being assessed to lower the melting point for rework/repair applications and devices where significant thermal mass influences the required dwell-time during assembly process.

6.1.3 Copper Dissolution N S W C C r a n e L e a d F r e e C o n t r o l P l a n • Dissolution of copper as a result of exposure to molten solder 30.64μm 0.00μm

6.1.3 Copper Dissolution N S W C C r a n e L e a d F r e e C o n t r o l P l a n • The higher Sn content and increased temperatures used in Pb-free soldering processes greatly increase the dissolution rate of copper from traces, plated-through holes, and pads exposed to the liquid solder during assembly and rework/repair. Under common conditions, the dissolution rates may be so high that plated-through-holes and pads are almost completely dissolved within 20 to 30 seconds using solder fountain methods. Multiple studies have identified that the copper dissolution rate of SnCu and SnAgCu alloys soldered through-hole circuit boards is so great that an assembly can be reworked a maximum of one time using the solder fountain method, an unacceptable consequence for military hardware with a lifecycle of 20-30 or more years.

6.1.4 Cross-Contamination N S W C C r a n e L e a d F r e e C o n t r o l P l a n • Alloy Proliferation • One study shows 0.5% Pb in Pb-free solder reduces reliability by 50% • Placing a SnPb component in a Pb-free CCA could cause serious reliability issues • Compatibility between alloys is unknown

6.1.4 Cross-Contamination N S W C C r a n e L e a d F r e e C o n t r o l P l a n • As Pb-free COTS hardware is introduced into legacy SnPb systems, the potential for cross-contamination of metallurgies during rework is greatly increased. This will be complicated further by the replacement of SnPb finished piece-parts with Pb-free finishes. During the rework process, mixing metallurgy is a major concern for the long-term reliability of the product. A Pb-free BGA placed in a SnPb assembly using SnPb rework procedures will result in significantly reduced reliability and premature failure. A SnPb finished piece-part placed in a COTS Pb-free assembly containing a Bismuth alloy will also have reduced reliability. The intentional or unintentional mixing of SnPb and Pb-free solder and piece-part finishes will increase the risk of cross-contamination throughout a products service life and during each rework cycle. • 6.1.4.1 Pb-free Terminations in SnPb Joints • The variety and compositions of the Pb-free surface finishes being delivered into the electronics industry is extensive. From a solder joint reliability viewpoint, most Pb-free piece-part finishes are compatible with SnPb solder and processes. The exceptions are area array BGA and CSP components whose attachment spheres do not fully melt when processed using SnPb procedures. While the impact is not universal, the causes for these solder joint integrity issues must be prevented through piece-part and assembly alloy validation prior to rework. This LFCP prohibits the introduction of Pb-free area array components into assemblies containing SnPb solder alloys.

6.1.4 Cross-Contamination N S W C C r a n e L e a d F r e e C o n t r o l P l a n • 6.1.4.2 SnPb Terminations in Pb-free Joints • The introduction of SnPb terminated components in a Pb-free solder system is likely during the early stages of Pb-free assembly processing while the piece-part supply stream still contains SnPb terminated components. In addition, fine pitch leaded components <0.65mm (0.025”) have been granted an EU exemption and may continue to be available with SnPb finish. Concerns exist when SnPb finished components are introduced into Pb-free solder alloys containing Bismuth. • 6.1.4.3 Bismuth • The addition of bismuth (Bi) to SAC yields a solder joint with improved reliability. However, when Bi and Pb are intermixed in the solder joint, a low melting point SnBiPb ternary alloy can form under certain situations. The melting point of the ternary alloy is 96°C causing the solder joint to be susceptible to partial reflow during hot mission environments.

6.1.4 Cross-Contamination N S W C C r a n e L e a d F r e e C o n t r o l P l a n • 6.1.4.4 SnPb Finish in SnBi Solder Alloy • Trace amounts of Pb have a detrimental effect on solder life of SnAg and SAC solders containing 3-5% Bi in the solder alloy and resulted in catastrophic failure of Sn58Bi solder joints. Since the repair infrastructure may have both SnPb and Pb-free alloy configurations for a significant amount of time, it is imperative that parts screening be conducted to identify component termination finish. SnPb finished components shall not be used to assemble or rework Pb-free assemblies containing Bi in the solder alloy. • 6.1.4.5 SnBi Finish in SnPb Solder Alloy • In the transition to Pb-free electronics, some piece-parts are now only available with a SnBi termination finish. Testing shows that a SnBi termination finish containing 2-4% Bi is not detrimental to SnPb solder life. The use of SnBi termination finishes where the Bi content is ≤4% is permissible in SnPb soldered assemblies.

6.1.5 Processing Temperatures N S W C C r a n e L e a d F r e e C o n t r o l P l a n • Pb-free alloys melt ~30° C over SnPb • Potential damage to piece parts and circuit boards

6.1.5 Processing Temperatures N S W C C r a n e L e a d F r e e C o n t r o l P l a n • Pb-free solders typically have melting points 30-40°C higher than SnPb solder, require a longer dwell time to acquire fully liquidous state, and require changes to the flux properties. This requires a significant process change from the traditional SnPb methods. For systems designed and produced using SnPb, a major concern in the switch to Pb-free solders is the impact higher reflow temperatures have on materials designed and qualified for SnPb processing. Pb-free soldering processes impart significant stress on laminate and component materials. Common problems include board delamination and warping, popcorn cracking, and molding compound delamination from the lead frame. For new system acquisition, the issue of material selection must be actively addressed to avoid like situations.

6.2 Risk Management N S W C C r a n e L e a d F r e e C o n t r o l P l a n 6.2.1 Risk Assessment 6.2.2 Risk Response Strategies 6.2.3 Risk Management for Pb-free 6.2.4 Commercial-Off-The-Shelf (COTS) Equipment

6.2.1 Risk Assessment N S W C C r a n e L e a d F r e e C o n t r o l P l a n

6.2 Risk Management N S W C C r a n e L e a d F r e e C o n t r o l P l a n • Employment of risk management and risk management principals is required to deal with the identified Pb-free risk factors to eliminate or at least minimize any potential negative impact on the performance and reliability of military electronics performing in military environments. • 6.2.1 Risk Assessment • The most effective form of risk assessment is quantitative. Unfortunately, at this time there is little in the way of meaningful data with respect of Pb-free performing in military environments from which to conduct such a quantitative analysis. No one can say with any certainty that because of tin whiskers (or any other risk factor) the reliability of a system will be reduced by a specific percentage. Therefore, a qualitative risk assessment is in order. Figure 1 is a qualitative analysis of the probability and impact of each risk factor identified previously. • The probability that tin whiskers will form approaches certainty when 100%Sn component termination finishes are used. However, for the various tin whisker variables, the probability is much less sure: the number of whiskers that will form; the lengths to which will grow; will any reach and short adjacent terminations; will any fracture, fall off, and cause shorts; etc. This makes the potential impact range for tin whiskers from moderate to quite high. The assessment of copper dissolution is similar to tin whiskers with the probability of occurrence being high and the potential impact ranging from moderate to high. The risk factor, cross-contamination, differs with respect that its potential impact ranges from very low to moderate. Processing temperatures has similar impact range as cross-contamination, but its probability of occurrence is moderate. Finally, the risk factor, solder joint reliability, has a moderate probability of occurrence, but its potential impact covers the whole spectrum from low to high.

6.2.2 Risk Response Strategies N S W C C r a n e L e a d F r e e C o n t r o l P l a n • Acceptance • Avoidance • Transfer • Mitigation

6.2 Risk Management N S W C C r a n e L e a d F r e e C o n t r o l P l a n • 6.2.2 Risk Response Strategies • There are four types of response strategies to manage or counter risks having negative impacts: • Accept—do nothing and deal with the impact should it occur • Avoid—eliminate the threat or the possibility of having any impact • Transfer—shift responsibility to another party, (i.e. warranties) • Mitigate—reduce the probability of occurrence and/or reduce the impact if it does occur • 6.2.3 Risk Management for Pb-free • As described previously, the increased risk factors resulting from the transition to Pb-free in military high-reliability electronics are tin whiskers, solder joint reliability, copper dissolution, cross-contamination, and increased processing temperatures. Table 1 shows the limited introduction of Pb-free at NSWC Crane and how risk management will be accomplished through the risk response strategies employed. The columns first categorize the solder, component, and board finish variables; followed by the risk response strategy for each of the risk factors identified; and finally, name the column with a solder process identifier. For the risk response strategy blocks, the green (avoid) blocks denote no increased risk; the yellow-green (mitigate/accept) show little increased risk; the yellow (mitigate) show low to moderate increased risk; and the red (accept) blocks show moderate to high increased risk.

Risk Factors N S W C C r a n e L e a d F r e e C o n t r o l P l a n • Tin Whiskers • Solder Joint Reliability • Copper Dissolution • Cross Contamination • Processing Temperatures • Component Reliability

6.2.3 Risk Management for Pb-free N S W C C r a n e L e a d F r e e C o n t r o l P l a n

6.2 Risk Management N S W C C r a n e L e a d F r e e C o n t r o l P l a n • 6.2.3 Risk Management for Pb-free • One of the potential risk management techniques hot solder dipping (HSD) does itself create an additional risk factor–component reliability. HSD reprocesses pure Sn component terminations by adding at least 3% Pb. Because HSD does reheat the component, there is potential for introducing latent defects. • Of the seven processes identified above in Table 1, the standard and preferred soldering process in use at NSWC Crane for all applications is: • SnPb process—Sn37Pb solder/SnPb board finish/SnPb component termination finishes. The SnPb Process consists of the Sn37Pb[1] solder alloy[2]; the board finish contains a minimum of 3% Pb; and the component termination finishes also contain a minimum of 3% Pb.

6.2.3 Risk Management for Pb-free N S W C C r a n e L e a d F r e e C o n t r o l P l a n

6.2.3 Risk Management for Pb-free N S W C C r a n e L e a d F r e e C o n t r o l P l a n Au NiPd NiPdAu ENIGImAg OSP

6.2.3 Risk Management for Pb-free N S W C C r a n e L e a d F r e e C o n t r o l P l a n HotSolder Dip

6.2.3 Risk Management for Pb-free N S W C C r a n e L e a d F r e e C o n t r o l P l a n Pure Tin

Crane Division, Naval Surface Warfare Center Lead Free