Presentation is loading. Please wait.

Presentation is loading. Please wait.

Annual ESA School Meeting, Portsmouth University, 17- 02-10 Grazyna Mozdzen AMAT – Advanced Materials and Aerospace Technology Electronic Materials and.

Similar presentations


Presentation on theme: "Annual ESA School Meeting, Portsmouth University, 17- 02-10 Grazyna Mozdzen AMAT – Advanced Materials and Aerospace Technology Electronic Materials and."— Presentation transcript:

1 Annual ESA School Meeting, Portsmouth University, Grazyna Mozdzen AMAT – Advanced Materials and Aerospace Technology Electronic Materials and Assembly Processes for Space Workshop – University of Portsmouth G. Mozdzen, F. Rüdenauer, W. Costin, L. Schorn ENIG Finishing and „Black Pad“ Phenomenon

2 Annual ESA School Meeting, Portsmouth University, Grazyna Mozdzen AMAT – Advanced Materials and Aerospace Technology Content PCB – short time in use – detachment of BGA – failure analysis -Investigation of BGA and corresponding area on PCB -Investigation of conductive paths Metallographic investigations of PCBs with ENIG finishing with respect to “Black Pad” phenomenon PCB after 100 thermal cycles in the temperature range between -10 and +60°C PC boards have been delivered by ESA-ESTEC

3 Annual ESA School Meeting, Portsmouth University, Grazyna Mozdzen AMAT – Advanced Materials and Aerospace Technology Methods High Resolution Scanning Electron Microscopy (HRSEM) Light Microscopy (inverse metallographic microscope) Energy Dispersive Spectroscopy (EDS) Focused Ion Beam (FIB – CrossBeam Workstation)

4 Annual ESA School Meeting, Portsmouth University, Grazyna Mozdzen AMAT – Advanced Materials and Aerospace Technology PCB BGA Failure Analysis Assumption “Black Pad” What is “Black Pad”? BGA - Bonding traces on solder balls PCB - Bonding traces on conductive pads

5 Annual ESA School Meeting, Portsmouth University, Grazyna Mozdzen AMAT – Advanced Materials and Aerospace Technology “Black Pad” – Definition It causes poor solderability and consequently it is responsible for weakness of solder joints. Origin of “Black Pad” - corrosion of Ni during the Nickel deposition ( e.g. M. Walsh ) or/and during the Gold Immersion process ( e.g. R. A Bulwith, N. Biunno,..,) and formation of P-rich layer on the top of EN film. The corrosion process starts on the Nickel nodule boundaries causing spikes and propagates inside the nodules. On the corroded surface no or very poor IMCs developed during soldering. The corrosion due to IG process can be control by sufficient IG-bath parameters (e.g. pH, temperature, process duration). “Black Pad” phenomenon – black or grey appearance of the conductive pads. I: ENIG finishing – P enrichment on EN surface due to corrosion (Ni-bath, Au-bath) II: Soldering - P- enrichment on the interface; EN-to-solder due to formation of IMCs III: Solder joint - IMCs embedded in P-rich “underground” as a result of II or I+II No “Black Pad” phenomenon “Black Pad” phenomenon Solder Joint and P - enrichment

6 Annual ESA School Meeting, Portsmouth University, Grazyna Mozdzen AMAT – Advanced Materials and Aerospace Technology BGA detached from PCB / EDS Surface Analysis 20 kV – high activation volume information from large volume 10 kV – low activation volume information from area close to the surface Q; How can we prove a P enrichment on the detached surfaces? A; By using low and high accelerating voltages PCBBGA Conclusion Failure (detachment) due to “Black Pad” effect To early for conclusions an indication of “Black Pad” but no an evidence

7 Annual ESA School Meeting, Portsmouth University, Grazyna Mozdzen AMAT – Advanced Materials and Aerospace Technology EDS Surface Analysis – Interface Composition It has been reported that during reflow Ni 3 P has formed, consequently the black interlayer between IMCs and EN-film consists predominately of this phase (P. Snugovsky – Celestica Inc., Materials Science Lab.), Q; Could we confirm such a finding taking into account our results of chemical analysis? A; we can not confirm observation of P. Snugovsky The top of EN film consists of P, only small amount of Ni 3 P possible Q; Did Sn enrich on the pads surface ? A; According to EDS surface analysis - yes

8 Annual ESA School Meeting, Portsmouth University, Grazyna Mozdzen AMAT – Advanced Materials and Aerospace Technology BGA detached from PCB / Surface Analysis PCBBGA High density of elongated convex structures (width < 1µm) High density of elongated concave structures (width < 1µm) Elongated convex structures on the BGA side correlate with elongated concave structures on the PCB side

9 Annual ESA School Meeting, Portsmouth University, Grazyna Mozdzen AMAT – Advanced Materials and Aerospace Technology BGA detached from PCB / Surface Analysis Q; What is the chemical composition of the elongated structures? A; BGA side – the elongated convex structures consist predominately of Pb. BGAPCB A; PCB side – the elongated concave structures are partly filled with Sn.

10 Annual ESA School Meeting, Portsmouth University, Grazyna Mozdzen AMAT – Advanced Materials and Aerospace Technology BGA – Solder Ball - Cross Section Q; Do we observe IMCs ? BGA Solder Ball A; IMCs are present on the BGA surface, the width of IMC zone ~ 4 µm

11 Annual ESA School Meeting, Portsmouth University, Grazyna Mozdzen AMAT – Advanced Materials and Aerospace Technology ~ NiSn (Ni 3 Sn 4 ) Q; Which phases have formed during soldering? ~ Ni 3 Sn 7 A; NiSn and Ni 3 Sn 7 could be detected by EDS analysis Brittle phase of the type Me 3 Sn ((Ni+Au) 3 Sn) which is believed to be detrimental for the strength of the bonding has not been identified BGA – Solder Ball - Cross Section

12 Annual ESA School Meeting, Portsmouth University, Grazyna Mozdzen AMAT – Advanced Materials and Aerospace Technology PCB - Cross Sections The surface analysis revealed Sn inside the cavities as well as P and Sn enrichment on the surface (close to the surface) Sn Ni Cu P Au Pb FIB cut The elongated concave structures are partly filled with Sn. P-enrichment close to the surface, Presence of Sn on the surface Q; Does analysis of the cross section confirm the results of the surface analysis ? A; Results of the surface analysis have been confirmed by the results of the cross section analysis

13 Annual ESA School Meeting, Portsmouth University, Grazyna Mozdzen AMAT – Advanced Materials and Aerospace Technology BGA detached from PCB / Summary BGA side Presence of IMC – ~NiSn, ~Ni 3 Sn 7 No presence of the brittle phase - Ni 3 Sn High density of the elongated convex structures (width < 500nm) Elongated convex structures are predominately composed of Pb P-enrichment close to the EN surface (~300nm layer) P rich layer may contain small amount of Ni 3 P Presence of Sn on the surface (~ 100nm film) Presence of elongated concave structures Elongated concave structures are partly filled with Sn PCB side Elongated convex structures on the BGA side correlate with elongated concave structures on the PCB side

14 Annual ESA School Meeting, Portsmouth University, Grazyna Mozdzen AMAT – Advanced Materials and Aerospace Technology Additional Information needed for Interpretation and Conclusions Investigation of conductive paths present on PCB Area with middle stage of corrosion, distinct nodule boundaries

15 Annual ESA School Meeting, Portsmouth University, Grazyna Mozdzen AMAT – Advanced Materials and Aerospace Technology Additional Information needed for Interpretation and Conclusions Investigation of conductive paths present on PCB Corroded nodule boundaries correlate with spikes - corrosion continuous from surface towards interior FIB cut Black bands (Black Pad phenomenon) below Au film visible

16 Annual ESA School Meeting, Portsmouth University, Grazyna Mozdzen AMAT – Advanced Materials and Aerospace Technology Investigation of conductive paths present on PCB P-enrichment - “Black Pad” phenomenon occurs locally Black bands (“Black Pad” phenomenon) below Au film <~ 100nm Au film ~ 300nm Conductive paths on the investigated PCB exhibit mostly an early stage of “Black Pad” phenomenon

17 Annual ESA School Meeting, Portsmouth University, Grazyna Mozdzen AMAT – Advanced Materials and Aerospace Technology BGA detached from PCB / Interpretation Elongated concave structures on the surface of conductive pads correspond with spikes which have been formed due to corrosion during GI process. Corrosion caused besides formation of the spikes also P - enrichment on the top of EN film - “Black Pad” phenomenon Elongated structures are an indirect proof for “Black Pad” phenomenon because P-enrichment on the interface EN-to-solder could be an effect of IMC formation as well. The separation of BGA from PCB refers to “Black Pad” phenomenon This conclusion is supported by the “Black Pad (Band)” phenomenon which could be identified at the conductive paths from the corresponding board. spikeelongated structure

18 Annual ESA School Meeting, Portsmouth University, Grazyna Mozdzen AMAT – Advanced Materials and Aerospace Technology BGA detached from PCB / Mechanism  Corrosion due to EN deposition or/and GI process - formation of spikes and P rich layer of the top of conductive pads – “Black Pad” phenomenon  Soldering – extension of P-rich zone due to formation of IMCs, formation of a certain amount of Ni 3 P possible  IMCs embedded in a very weak “underground” – no or poor bonding  Reaction of Sn with Ni is impaired (stopped) because of P enrichment and of a deficit of Ni (small amount of Ni in P-rich layer is bonded to Ni 3 P)  Further diffusion of Pb and Sn towards the interface, (Sn diffusion rate higher than the Pb), Sn partly deposits on the interface; IMCs-to-EN and partly into the spikes.  Formation of elongated structures (convex – side of solder balls, concave- on the conductive pads) which provide a weak mechanical bonding between BGA and PCB BGA detached from PCB during service due to e.g. even very slight vibration

19 Annual ESA School Meeting, Portsmouth University, Grazyna Mozdzen AMAT – Advanced Materials and Aerospace Technology ENIG Finishing and „Black Pad“ Phenomenon/ Discussion Strength of Bonding ProsCons Composition uniformity, Corrosion resistance, Good solderablility, Cheap, well established – opitimised, …….., Ni-bath, Au-bath – in order to avoid “Black Pad” phenomenon a huge number of parameters has to be balanced therefore the possibility of “Black Pad” is very high. Early stage of “Black Pad” almost always present Even an early stage of “Black Pad” can be very detrimental for a bonding strength if it sums up with P-enrichment caused by IMCs formation during soldering. Formation of IMCs and bonding strengthening P-enrichment on the interface; IMCs-to-EN as a natural effect of the bonding Two coupled processes which are running in opposite directions

20 Annual ESA School Meeting, Portsmouth University, Grazyna Mozdzen AMAT – Advanced Materials and Aerospace Technology ENIG Finishing – example of „Black Pad“ Phenomenon Example of locally occurred “Black Pad” phenomenon, smooth surface, spikes, no adhesion PCB after thermal cycling (100 cycles -10 and + 60°C) Conductive pad after pulling off of an IC strand

21 Annual ESA School Meeting, Portsmouth University, Grazyna Mozdzen AMAT – Advanced Materials and Aerospace Technology „Black Pad“ Phenomenon - Conclusions Even an early stage of “Black Pad” can be detrimental for the strength of a bonding if it sums up with P-enrichment caused by IMCs formation during soldering. Early stage of corrosion (early stage of “Black Pad” phenomenon) can only be recognised at high magnification (SEM analysis necessary). This impedes significantly a quality control of PCB. Formation of IMCs does assure a good bonding since even more or less well developed IMCs will separate from conductive pads if the interface between the IMCs and an EN film is weak (interface which predominately consists of P or of P + Ni 3 P). Formation of interleaved elongated structures due to presence of spikes in an EN film (solder ball - convex, EN surface - concave) may simulate a good bonding. An assembly with such a bonding is difficult to sort out. The risk of a failure of PCBs with ENIG finishing increases dramatically if the boards are exposed to vibration, mechanical shock or thermal cycling. Detachment of BGA solder ball from Ni surface Bruce Hough “ Solving the ENIG Black Pad Problem: An INTRI Report on Round 2”

22 Annual ESA School Meeting, Portsmouth University, Grazyna Mozdzen AMAT – Advanced Materials and Aerospace Technology Thank you for Attention


Download ppt "Annual ESA School Meeting, Portsmouth University, 17- 02-10 Grazyna Mozdzen AMAT – Advanced Materials and Aerospace Technology Electronic Materials and."

Similar presentations


Ads by Google