remap materials project m2: high temperature high … · 2018-05-23 · remap materials project m2:...

REMAP MATERIALS PROJECT M2: HIGH TEMPERATURE HIGH HUMIDITY CORROSION AND TIN WHISKER EVALUATION OF BI

CONTAINING LEAD-FREE ALLOYS

Polina Snugovsky#, Stephan Meschter*, Jeff Kennedy#, and Zohreh Bagheri#, #Celestica Inc., Toronto, ON, Canada

*BAE Systems, Endicott, N.Y. [email protected]

ABSTRACT The introduction of environmental legislation such as the European Union’s Restriction of Hazardous Substances (RoHS) directive has led to the use of new tin-based solder alloys in electronics manufacturing. These alloys have shown a susceptibility to the spontaneous growth of filaments known as tin whiskers. Over time, this can cause field failures in high-reliability applications such as aerospace, medical and automotive electronics. This project will focus on the greening of aerospace electronics materials to reduce the risk of tin whiskers and increase electronics reliability for applications that are exposed extreme conditions. The whisker growth and corrosion of assemblies soldered with Bi additions to Sn-Ag-Cu and Sn-Cu alloys were evaluated in high temperature/high humidity 85C and 85 percent relative humidity environments using boards with ENIG and immersion Sn board finishes. BACKGROUND The elimination of lead (Pb) from consumer electronics has resulted in an increased emphasis on tin whisker risk mitigations in aerospace and defense systems using dual-use commercial/aerospace components [1]. Environmental prohibitions of lead in commercial electronics have made these electronic parts and assemblies become more susceptible to tin whiskering. Tin whisker shorting issues were known to be an issue decades ago and at that time whisker issues were solved by the addition of lead into tin. Unlike consumer electronics, aerospace systems can have high consequences of failure and are exposed to many kinds of environmental conditions that promote whisker growth. Some conditions of concern are thermal cycling, vibration, shock, humidity, salt fog, sulfur rich environments, rework, and long term storage. Figure 1 shows several sources of compressive stress in a typical tin plated lead and solder joint.

Figure 1: Sources of compressive stress contributing to whisker growth. The dynamic recrystallization model provides a useful means to describe whisker growth [2]. An interesting aspect of the dynamic recrystallization model is that for a given temperature and grain size if the compressive stress in the tin is either too low or too high, whisker growth does not occur. Although lead has demonstrated effectiveness at reducing whisker propensity, tin alloying elements can either increase or decrease whisker growth in Sn plating [3] [4]. A short duration Sn plating study indicated that Bi addition tended to retard whisker growth [5]. However, prior soldered assembly tin whisker testing revealed that the entire material system of the lead-free solder joint must be considered when evaluating tin whisker growth (e.g. lead material, lead finish, solder alloy, board pad finish, board pad material, and the type/location of intermetallics within the joint) [6]. Solder can have significant whisker growth due to corrosion between different intermetallics in the alloy when contamination is present [7]. The whisker propensity of bismuth containing lead-free alloys is the main thrust of the present evaluation. Here an 85C/85 percent relative humidity environment is used, similar to the soldered assembly tin whisker growth test previously performed on SAC305 (Sn-3.0Ag-0.5Cu) [6].

TEST VEHICLE AND ENVIRONMENT Three custom designed test vehicles were used for the lead-free soldered assembly whisker growth testing. The boards were soldered twelve at time on the panel shown in Figure 2. The individual printed circuit boards are 6 cm x 6 cm x 2.36 mm thick double sided glass epoxy with one ounce copper external base layers (Table 1). The boards use high temperature FR4 and are manufactured in accordance with IPC-6012 Class 3, Type 2. All boards have solder mask in accordance with IPC-SM-840 Class H, liquid photo-imageable over bare copper. The exposed traces, pads and plated through holes are either immersion tin (Imm Sn) finished in accordance with IPC-6012, Type IT or immersion gold over electroless nickel (ENIG) in accordance with IPC-6012, type ENIG with solderability meeting the requirements of ANSI/J-STD-003, Class 3, Category 2. The test vehicles are designated by the main types of parts they contain: SOT (small outline transistor), QFP (quad flat pack) and BGA/CAP (ball grid array/capacitor). The boards are shown in Figure 3 to Figure 5 and the part types are given in Table 2 to Table 4. The boards on the panels were soldered in accordance with J-STD-001 Class 3, using the alloys in Table 5. Convection reflow was done using a solder paste with the cleanable no-clean fluxes in (Table 5). Note that a 180° glass transition temperature (Tg) board laminate was used to accommodate the SAC305 soldering temperature although Bi containing alloys could use lower Tg board materials, which are more resistant to pad cratering, because of their lower melting points. For the whisker testing, three low melting point Bi containing alloys were compared to a SAC305 baseline used in prior testing [6][7]. No special piece-part cleaning was performed prior to soldering. After soldering, the boards were cleaned with a conventional in-line cleaner. Each of the three boards was laid out with whisker testing in mind. The test vehicles fit easily into the scanning electron microscope (SEM) sample chamber. The part placement area was limited to 5 cm x 5 cm to ensure all leads of interest were contained in a region that could be viewed by the SEM. The boards were laid out with all components on a single side of the assembly. This simplified the manufacturing process, and prevented any components from seeing additional reflow profiles as a consequence of being on the bottom side of the printed circuit board. Efforts to simplify the inspection process were also made. Components were laid out in blocks of the same component type, which made the groupings easy to identify, and allowed the components to be laid out in straight rows. By placing the components in rows, the leads were aligned in a single plane, allowing the SEM operator to pan along the entire row without having to make excessive adjustments. In addition, silkscreen marks spaced every 0.254 cm on the perimeter of the

board to improve area tracking on the board. Each board is designed with enough parts to have 50 to 100 leads for each part type.

After cleaning, the assemblies were exposed to 85 C/85 percent relative humidity in the chamber shown in Figure 6. The temperature control was performed using thermocouples and humidity was controlled using both dry bulb temperature and wet bulb temperatures. A sheet metal shield was placed above the samples to ensure no condensation would collect on the samples.

Figure 2: Test vehicle assembly panel. Table 1: Printed wiring board parameters.

Parameter 236C1829P1 236C1829P2

Dimensions (in) 9.7280 0.010 x

7.8800 0.010

Thickness (in) 0.093 0.007

Laminate PCL-FR-370HR Isola

Laminate Tg 180°C

Number of Layers 2

Surface Finish Imm Tin ENIG

Surface Finish Layer Thickness( micro-inch)

Sn: 53.5 1.7

Au: 2.9 0.1 Ni: 174.5 4.6

Copper Plating

Thickness (micro-inch) 0.0018 0.00153

Measured CTE,

x, y-direction (ppm/C) 13/14

Measured CTE,

z- direction (ppm/C) 45

Figure 3: SOT test vehicle.

Figure 4: QFP test vehicle.

Figure 5: BGA/CAP test vehicle.

Table 2: SOT board parts. Designation

Part No. Package

Lead Frame

(4)

Lead finish

No. of leads per part/

No. of parts SOT3

2N7002 (1) SOT23-3

Alloy 42 Matte

Sn 3/64

SOT5 NC7S08M5X (2)

SOT23-5 Cu194

Matte Sn

5/40

SOT6 2N7002DW-7-F

(1) SOT363 Alloy 42

Matte Sn

6/17

R0402 0402- Pb-free Chip resistor

Alumina Matte

Sn 2/128

Notes: (1) Fairchild; (2) Diodes Inc.; (3) Practical Components (Amkor); (4) From the manufacturer’s data sheet Alloy 42 is Fe39-41Ni-0.6Mn-0.05Cr-0.02Si-0.05C and Cu194 alloy is Cu 2.1-2.6Fe 0.015-0.15P 0.05-0.2Zn

Table 3: QFP board parts.

DesignationPart No.(1) Package

Lead Frame

(2) Lead Finish

No. of Leads/No.

of parts QFP44

A-QFP44-10mm-.8-3.2-DC-Sn (1) (0.8 mm pitch)

C7025 Tin 44/6

PLCC20A-PLCC20T-DC-Sn

(1) (1.25 mm pitch)

C151 Tin 20/4

TQFP64A-LQFP64-.7mm-

.4mm-2.0-DC-Sn (1)(0.4 mm pitch)

C7025 Tin 64/4

R0603 0603 - Pb-free (1)

Alumina Tin 2/20

Notes: (1) Practical Components (Amkor); (2) From the manufacturer’s data sheet C7025 is Cu 2.2-4.2Ni 0.25-1.2Si 0.05-0.3Mg and C151 is Cu0.1Zr

Table 4: BGA/CAP board parts. Designation

Part No. Package (1)

Substrate material

Ball or Termination

Material

No. of Parts

BGA100 A-CABGA100-

0.8mm-10mm-DC BGA

NA SAC305 4

BGA97 A-CVBGA97-

0.4mm-5mm-DC BGA

NA SAC305 5

C1206 C1206C103KDRAC Ceramic capacitor

C06 ceramic

Tin 32

C0603 C0603C471F5GAC Ceramic capacitor

C06 ceramic

Tin 48

C0402 C0402C101K3GAC Ceramic capacitor

C06 ceramic

Tin 42

Note: (1) BGAs are from Practical Components (Amkor) and capacitors are from Kemet.

Table 5: Solder assembly alloys and fluxes.

Solder Composition

(weight percent) Flux

SAC305 96.5-Sn, 3-Ag, 0.5-Cu INDIUM8.9HF

Senju M42 94.25-Sn, 2-Ag, 0.75-Cu,

3-Bi INDIUM8.9HF

Sunflower 92.3-Sn, 0.7-Cu, 7-Bi INDIUM8.9HF

Violet 91.25-Sn, 2.25-Ag, 0.5-

Cu, 6-Bi INDIUM8.9HF

SnPb 63-Sn 37-Pb NC-SMQ92J

Figure 6: Temperature/humidity chamber

WHISKER INSPECTIONS A scanning electron microscope (SEM) was used for the inspection and an electron dispersive X-Ray (EDX) was used for elemental analysis. The first inspection was

performed after 1,000 hours. Following the inspection, the samples returned into the chamber and re-inspected after an additional 3,000 hours for a total of 4,000 hours (1,000h + 3,000h). The present work describes the preliminary screening inspection on selected parts from the SOT, QFP and BGA assemblies. WHISKER GROWTH RESULTS 1,000 hour inspection Detailed inspection images of oxidation/corrosion and whiskers after 1,000h of 85C/85%RH are shown in Appendix A. The corrosion and whisker growth observations are summarized next. Alloy influence on oxidation/corrosion: Comparing alloys on an ENIG finish for the R0402 the SAC305 may have slightly more oxidation/corrosion than Senju. For the ENIG board finish soldered SOT5 there was no difference among SAC305, Senju, Sunflower and Violet. For the Imm Sn board finish soldered C1206 there was some oxidation/corrosion on all alloys, pads and part terminations. There was no difference between SAC, Senju and Sunflower. Violet was less corroded. Board finish influence on oxidation/corrosion: Comparing board finish, Imm Sn generally had more oxidation/corrosion than ENIG (e.g. Figure 7 and Figure 8). For the Sunflower soldered SOT5 there was some corrosion on the ENIG but more on the Imm Sn. Tin whiskers: Short tin whiskers, less than five micron long, observed on the Senju and the Sunflower alloys. The SOT5 soldered with Sunflower on ENIG board pads (Figure 9 and Figure 10) was higher than the Senju.

Figure 7: SOT5, SAC305, ENIG, 1,000h, 100x.

Figure 8: SOT5, SAC305, Imm Sn, 1,000h, 100x. Arrows indicate corrosion.

Figure 9: Corrosion on top of the lead and short whiskers on the side of the lead for the SOT5, Sunflower, ENIG, 1,000h, 200x.

Figure 10: Higher magnification images of the whiskers on SOT5, Sunflower, ENIG, 1,000h, 2,000x and 2,500x. 4,000 hour inspection The corrosion and whisker growth increased significantly between the 1,000 and the 4,000 (1,000 + 3,000) hour inspections. Detailed inspection images are shown in Appendix B. The corrosion and whisker growth observations are summarized in Table 6 and Table 7 and discussed next. Corrosion: Generally, the corrosion was less on ENIG than Imm Sn as shown for the SOT5 soldered with SAC305 (Figure 11 and Figure 12). Note that the SOT5 soldered with SAC305 to Imm Sn exhibited a range of corrosion from light to significant (Figure 12).

Greater corrosion with the Imm Sn finish was generally observed on the Bi containing alloys than SAC305. The SOT5 on ENIG soldered with the Violet alloy had no corrosion (Figure 13), but on Imm Sn had heavy corrosion (Figure 14). In comparison, the SAC305 had slightly less corrosion (Figure 12A). The SOT5 soldered with Sunflower alloy on ENIG had light corrosion (Figure 15) and on Imm Sn had significant corrosion (Figure 16). The SOT5 soldered with Senju exhibited the greatest difference between ENIG (Figure 17) and Imm Sn finishes (Figure 18). Tin whiskers: Longer whiskers were observed on Imm Sn than on ENIG. SAC305 on Imm Sn exhibited the longest whisker growth (up to 200 microns). In some cases, the whiskers tended to grow in clusters along the board pad edge (Figure 19 and Figure 20). While Bi containing lead-free solder alloys on Imm Sn had somewhat greater corrosion than SAC305, Bi reduced whisker growth. For instance, on the SOT5 part, SAC305 without Bi on Imm Sn had whisker growth up to 200 microns. On the other hand Violet with six percent Bi had whisker lengths only up to 20 microns, Sunflower with seven percent Bi and no Ag had whiskers up to 35 microns and Senju with three percent Bi had whiskers up to 40 microns long. The whisker length was similar between the ENIG and Imm Sn pads for the Sunflower soldered SOT5 (Figure 21 and Figure 22). On the heavily corroded samples, the whisker still grew from the corroded areas (Figure 23). While many whiskers were curved, some were straighter (Figure 24 and Figure 25). It is unclear why the SOT3 (Fe-42Ni) exhibited longer whisker growth than the copper lead materials. In prior testing, the low coefficient of expansion alloy 42 lead material exhibited significant whisker growth in SAC305 assembly thermal cycling but delayed whisker nucleation in 85C/85%RH [6]. Detailed observations by alloy, part and board finish follow next: SAC305 SOT5

o ENIG – no whiskers o Imm Sn – up to 200 microns

SOT3 o ENIG – no whiskers o Imm Sn – up to 60 microns

QFP44 o ENIG – whiskers below 15 microns o Imm Sn – up to 50 microns

Violet SOT5

o ENIG –whiskers below 20 microns around Cu pads

o Imm Sn – corrosion and hollow whiskers and normal whiskers below 20 microns

SOT3 o ENIG –whiskers below 15 microns around Cu

pads o Imm Sn – corrosion and hollow whiskers and

normal whiskers below 15 microns QFP44

o ENIG –whiskers below 10 microns around Cu pads

o Imm Sn – corrosion and hollow whiskers and normal whiskers below 20 microns, possibly oxidized whiskers up to 40 microns

Sunflower SOT5

o ENIG –whiskers below 20 microns around Cu pads and on leads; More whiskers than on Violet

o Imm Sn – corrosion and hollow whiskers and normal whiskers up to 35 microns

SOT3 o ENIG – whiskers up to 20 microns around Cu

pads and on leads o Imm Sn - whiskers up to 75 microns

Senju SOT5

o ENIG – many whiskers below 40 microns and hollow whiskers around Cu pads; More whiskers than on Violet and Sunflower

o Imm Sn – excessive corrosion and hollow whiskers and normal whiskers about 40 microns

SOT3 o ENIG – many whiskers below 20 microns

around Cu pads; More whiskers than on Violet and Sunflower

o Imm Sn –whiskers up to 20 microns EDX analysis: An EDX examination of corrosion product found that the corrosion product was mainly tin oxide (or hydroxide) (Figure 26). The whisker region had tin, copper, bismuth, sulfur and oxygen (Figure 27). Since the parts were not pre-cleaned prior to assembly, the sulfur contaminate could have been from the parts as was observed in prior experiments [7]. DISCUSSION The extent of corrosion did not necessarily correlate to whisker growth. For instance, on the Imm Sn pads, shorter whiskers were observed on the Bi containing alloys than SAC305. It is possible that the more extensive corrosion of the thin tin rich regions consumed the tin that would have been available for whisker growth. Alternatively, a higher level of corrosion stresses was not as conducive to whisker growth as the stress from a lower corrosion level [2].

Table 6: Corrosion summary

Part Board Finish

SAC305 Violet Sun‐flower

Senju

SOT5 ENIG LC NC LC LC

SOT3 ENIG LC LC LC LC

QFP44 ENIG LC LC Not evaluated

QFP44 Imm Sn

SC SC

SOT5 Imm Sn

SC HC SC HC

SOT3 Imm Sn

SC HC HC HC

Corrosion level key:

NC No corrosion SC Significant

LC Light HC High

Table 7: Whisker summary

Part Board Finish

SAC305 Violet Sun‐flower

Senju

SOT5 ENIG No

whiskers Up to 20µm

Up to 20µm

Up to 40µm

SOT3 ENIG No

whiskers Up to 15µm

Up to 20µm

Up to 20µm

QFP44 ENIG Up to 15µm

Up to 10µm

Not evaluated QFP44

Imm Sn

Up to 50µm

Up to 20µm (40µ)

SOT5 Imm Sn

Up to 200µm

Up to 20µm

Up to 35µm

About 40µm

SOT3 Imm Sn

Up to 65µm

Up to 15µm

Up to 75µm

Up to 20µm

Whisker length key:

No whiskers Fails JESD201

Does not fail JESD201

Fails JESD201 Very long whiskers

Figure 11: SAC305, SOT5, ENIG, 4,000h, 100x. Light corrosion.

(A)

(B) Figure 12: SAC305, SOT5, Imm Sn, 4,000h, 100x; (A) whiskers and significant corrosion and (B) light corrosion.

Figure 13: Violet, SOT5, ENIG, 4,000h, 100x. Whisker growth on the board pad edge and no corrosion.

Figure 14: Violet, SOT5, Imm Sn, 4,000h, 100x. Heavy corrosion.

Figure 15: Sunflower, SOT5, ENIG, 4,000h, 100x.Light corrosion.

Figure 16: Sunflower, SOT5, Imm Sn, 4,000h, 100x.Significant corrosion.

Figure 17: Senju, SOT5, ENIG, 4000h, 100x.Light corrosion.

Figure 18: Senju, SOT5, Imm Sn, 4,000h, 100x. Heavy corrosion.

Figure 19: Whiskers on SAC305, SOT5, Imm Sn, 4,000h, 250x and 1,800x.

Figure 20: Senju, SOT5, ENIG, 4000h, 300x and 1,000x.

Figure 21: Sunflower, SOT5, ENIG, 4,000h, 1,200x.

Figure 22: Sunflower, SOT5, Imm Sn, 4,000h, 1,000x.

Figure 23: Senju, SOT5, Imm Sn, 4,000h, 1,500x.

Figure 24: Whisker on SAC305, SOT3 Imm Sn, 4,000h, 300x. Arrow highlights a 60 micron long whisker.

Figure 25: Whisker on SAC305, QFP44, Imm Sn, 4,000h, 1,000x and 3,000x.Small whisker diameter at the tip and a longer larger whisker diameter at the base.

Weight percent

O Cu Sn

Pt1 21.70 2.79 75.51

Pt2 24.76 6.94 68.30 Figure 26: EDX analysis of corrosion product on Senju, Imm Sn, SOT5, 4,000h (3,000+1,000).

Weight percent

O S Cu Sn Bi

Pt1 24.22 0.44 4.05 68.66 2.63

Pt2 14.67 0.16 1.25 83.81 0.11

Figure 27: EDX analysis of whisker on Senju, Imm Sn, SOT5, 4,000h (3,000+1,000).

SUMMARY The entire solder termination material content is important for corrosion and whisker growth. More solder corrosion was seen on Imm Sn than on ENIG. Longer whiskers were observed on Imm Sn than on ENIG. However, the relationship between whisker growth and corrosion is clear. While Bi containing lead-free solder alloys on Imm Sn had somewhat greater corrosion than SAC305, Bi reduced whisker growth. For instance, the SOT5 (Cu194) on Imm Sn soldered with SAC305 had whisker growth up to 200 microns, while the SOT5 Imm Sn maximum whisker length on Bi containing alloys ranged from 20 microns (Violet with six percent Bi), to 35 microns (Sunflower with seven percent Bi and no Ag), to 40 microns (Senju with three percent Bi) and 40 microns.

REFERENCES [1] GEIA-STD-0005-2, Standard for Mitigating the

Effects of Tin Whiskers in Aerospace and High Performance Electronic Systems, SAE International, Warrendale, PA.

[2] P. Vianco, and J. Rejent, Dynamic Recrystallization (DRX) as the Mechanism for Sn Whisker Development Part I: A Model, Journal of Electronic Materials, Volume 38, Number 9, pp. 1815-1825, 2009.

[3] G.T. Galyon, Annotated Tin Whisker Bibliography and Anthology, IEEE Trans. Packag. Manuf. Vol. 28, No. 1, January 2005, pp. 94-122.

[4] J. Nielsen and T. Woodrow, The Role of Trace Elements in Tin Whisker Growth, Project WP1751 Final Report for the Strategic Environmental Research and Development Projects (SERDP), September 22, 2013.

[5] I. Yanada, “Electroplating of Lead-Free Solder Alloys Composed of Sn-Bi and Sn-Ag, Proc. Of the IPC Printed Circuits Expo, Long Beach USA: pp. S11-2 to S11-2-7, April 1998.

[6] S. Meschter, P. Snugovsky, Z. Bagheri, E. Kosiba, M. Romansky, J. Kennedy, L. Snugovsky, and D. Perovic, Whisker Formation on SAC305 Soldered Assemblies, JOM, vol. 66 no. 11, pp. 2320-2333, Nov. 2014 (DOI) 10.1007/s11837-014-1183-9, available on line at

http://www.springer.com/home?SGWID=0-0-1003-0-0&aqId=2737780&download=1&checkval=c6d6cb73aec6cca572a5b064f23677b9

[7] P. Snugovsky, S. Meschter, Z. Bagheri, E. Kosiba, M. Romansky, and J. Kennedy, Whisker Formation Induced by Component and Assembly Ionic Contamination, Journal of Electronic Materials, February 2012, Volume 41, Issue 2, pp 204-223 available for download at http://link.springer.com/content/pdf/10.1007%2Fs11664-011-1808-5.pdf

Appendix A: 85°C/85%RH, 1,000 hour inspection detailed photographs, non-contaminated samples

Figure 28: C1206 SAC, ENIG, 1,000h, 40x and 100x.

Figure 29: C1206 Senju, ENIG, 1,000h, 40x and 100x.

Figure 30: C1206, Sunflower, ENIG, 1,000h, 40x and 100x.

Figure 31: R0402, SAC, ENIG, 1,000h, 40x and 100x.

Figure 32: R0402, Senju, ENIG, 1,000h, 40x and 100x.

Figure 33: R0402, Violet, ENIG, 1,000h, 40x and 100x.

Figure 34: R0603, SAC305, ENIG, 1,000h, 100x.

Figure 35: R0603 SAC305, Imm Sn, 1,000h, 100x and 400x. Arrow indicates corrosion.

Figure 36: C1206, SAC305, ENIG, 1,000h, 40x and 100x.

Figure 37: C1206 SAC305, Imm Sn, 1,000h, 40x and 100x.

Figure 38: C1206 Senju, Imm Sn, 1,000h, 40x and 100x.

Figure 39: C1206 Sunflower, Imm Sn, 1,000h, 40x and 100x.

Figure 40: C1206 Violet, Imm Sn, 1,000h, 100x.

Figure 41: SOT5, Senju, ENIG, 1,000h, 100x.

Figure 42: SOT5, Senju, Imm Sn, 1,000h, 100x. Arrow indicates corrosion.

Figure 43: SOT5, SAC305, ENIG, 1,000h, 100x.

Figure 44: SOT5, SAC305, Imm Sn, 1,000h, 100x. Arrows indicate corrosion.

Figure 45: SOT5, Violet, ENIG, 1,000h, 100x.

Figure 46: SOT5, Violet, Imm Sn, 1,000h, 100x.

Figure 47: Whiskers on C1206, Senju, ENIG, 1,000h, 1,800x.

Figure 48: Whiskers on C1206 Sunflower, ENIG, 1,000h, 1,000x.

Figure 49: Whiskers on C1206 Sunflower, Imm Sn, 1,000h, 1,000x.

Figure 50: Whiskers on C1206 Sunflower, Imm Sn, 1,000h, 1,500x.

Figure 51: Whiskers on SOT5, Sunflower, ENIG, 1,000h, 200x.

Figure 52: Whiskers on SOT5, Sunflower, ENIG, 1,000h, 2,000x.



Figure 55: Whiskers on SOT5, Sunflower, Imm Sn, 1,000h, 200x.

Figure 56: Whiskers on SOT5, Sunflower, Imm Sn, 1,000h, 1,500x.



Appendix B: 85°C/85%RH, 4,000h (1000 + 3000) non-contaminated samples.

Figure 59: SAC305, SOT5, ENIG, 4,000h, 100x.

Figure 60: SAC305, SOT5, Imm Sn, 4,000h, 100x. Corrosion varied considerably.

Figure 61: Whiskers on SAC305, SOT5, Imm Sn, 4,000h, 250x and 1,800x.

Figure 62: Violet, SOT5, ENIG, 4,000h, 100x.

Figure 63: Violet, SOT5, Imm Sn, 4,000h, 100x.

Figure 64: Violet, SOT5, ENIG, 4,000h, 1,500x.


Figure 66: Violet, SOT5, Imm Sn, 4,000h, 1,200x.

Figure 67: Sunflower, SOT5, ENIG, 4,000h, 100x.


Figure 69: Sunflower, SOT5, Imm Sn, 4,000h, 100x.


Figure 71: Sunflower, SOT5, ENIG, 4,000h, 1,200x and 1,000x.

Figure 72: Sunflower, SOT5, Imm Sn, 4,000h, 1,000x.

Figure 73: Senju, SOT5, ENIG, 4000h, 100x.

Figure 74: Senju, SOT5, Imm Sn, 4,000h, 100x.

Figure 75: Senju, SOT5, ENIG, 4000h, 300x and 1,000x.

Figure 76: Senju, SOT5, Imm Sn, 4,000h, 1,500x.

Figure 77: SAC305, SOT3, ENIG, 4,000h, 100x.

Figure 78: SAC305, SOT3, Imm Sn, 4,000h, 100x.

Figure 79: SAC305, SOT3 Imm Sn, 4,000h, 50x. There is a possible water drop on the solder mask on the left side of the pad.

Figure 80: Whiskers on SAC305, SOT3 Imm Sn, 4,000h, 300x and 1,500x. Arrow highlights a 60 micron long whisker.

Figure 81: Violet, SOT3, ENIG, 4,000h, 100x.


Figure 83: Violet, SOT3, ENIG, 4,000h, 1,500x.

Figure 84: Violet, SOT3, Imm Sn, 4,000h, 1,500x.



Figure 87: Sunflower, SOT3, ENIG, 4,000h, 1,000x and 1,500x.


Figure 89: Senju, SOT3, ENIG, 4,000, 100x.

Figure 90: Senju, SOT3, Imm Sn, 4,000h, 40x.

Figure 91: Senju, SOT3, ENIG, 4,000h, 500x and 1,500x.

Figure 92: Senju, SOT3, Imm Sn, 4,000h, 1,500x and 3,000x.

Figure 93: SAC305, QFP44, ENIG, 4,000h, 100x.

Figure 94: SAC305, QFP44, Imm Sn, 4,000h, 100x.

Figure 95: SAC305, QFP44, ENIG, 4,000h, 1,500x and 2,500x.

Figure 96: SAC305, QFP44, Imm Sn, 4,000h, 1,000x and 3,000x.

Figure 97: Violet, QFP44, ENIG, 4,000h, 100x.

Figure 98: Violet, QFP44, Imm Sn, 4,000x, 100x.

Figure 99: Violet, QFP44, ENIG, 4,000h, 1,500x and 1,800x.

Figure 100: Violet, QFP44, Imm Sn, 4,000h, 800x and 1,000x.

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