1
Failure Analysis of Solder Joints
and Circuit Boards
By: Roger Devaney
Hi-Rel Laboratories
2
Typical types of solder joints
3
PWB ILCs still cause many failures
4
Laminate stack up
• A layer of uncured prepreg is placed on each
side.
• Outer cores with the internal layers patterned
...
5
Laminate stack
• Laminate is now a single unified structure
6
Via holes are drilled
• Precision tungsten carbide drill bits are used to
drill holes where needed.
• Drilling results i...
7
Detail view of hole drill damage
8
Drill Damage
9
Nail heading due to a dull drill bit
10
Drill damage removed by etching
• A “witches brew” of HF and H2SO4 is used to
removed damaged glass fibers and smeared
...
11
Positive Etchback
12
Positive Etchback
13
Electroless copper plating
• Electroless copper plating covers entire board, especially
drilled hole walls.
• Provides ...
14
Electrolytic copper plating
• This is the conductor layer of copper applied
over the electroless copper.
15
PWB Microvia Failure
16
BGA Solder Joints
17
Traditional Sn-Pb eutectic joints Pb free solder joints
18
Head-on pillow (HoP) BGA joint
HoP is caused by:
•Solder paste printing and rheology issues
•Reflow temperature uneven ...
19
20
As BGAs get smaller they can be
more prone to failure
21
Failure of microBGA joint
22
Do Pb-free and Pb/Sn mix well?
23
BGA Dye & Pry Test
24
Dye & Pry Testing
• This is a quick/inexpensive way to look for
cracked or non-wetted BGA joints.
• Allows for simultan...
25
Dye & Pry Test Procedure
• Cut out device to be tested from the PCB
• Clean flux from under device and bake dry
• Immer...
26
Dye & Pry
27
Post-Pry inspection
28
Post-Pry inspection
29
Fatigue failure of Column Grid Array (CGA) solder joints
30
Flip Chip solder joints
31
Flip chip cracking due to flexure
32
Chip on chip with Au stud bumps
33
Au-Sn lid seal voids seen at x-ray; are they for real?
34
Au-Sn lid seal voids seen at x-ray; are they for real?
35
These voids are real!
36
Thermal Fatigue
• When the assembly is temperature or power
cycled the different materials in the attach want
to expand...
37
Solder fatigue in thru-hole joint
38
Thermal fatigue in gull-wing joints
39
Classic Solder Fatigue!
40
Temp cycle failure of a BGA joint
41
Black Pad failure
This only occurs on Electroless Nickel, Immersion Gold
(ENIG) finished devices & boards:
• ENIG has c...
42
Black Pad failure
43
Black Pad failure
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Oregon_Failure_Analysis_of_Solder_Joints__PCAs_October_2012

  1. 1. 1 Failure Analysis of Solder Joints and Circuit Boards By: Roger Devaney Hi-Rel Laboratories
  2. 2. 2 Typical types of solder joints
  3. 3. 3 PWB ILCs still cause many failures
  4. 4. 4 Laminate stack up • A layer of uncured prepreg is placed on each side. • Outer cores with the internal layers patterned are laid up in alignment jig. • Layers are laminated under heat and pressure.
  5. 5. 5 Laminate stack • Laminate is now a single unified structure
  6. 6. 6 Via holes are drilled • Precision tungsten carbide drill bits are used to drill holes where needed. • Drilling results in a damaged layer that must be removed by etching.
  7. 7. 7 Detail view of hole drill damage
  8. 8. 8 Drill Damage
  9. 9. 9 Nail heading due to a dull drill bit
  10. 10. 10 Drill damage removed by etching • A “witches brew” of HF and H2SO4 is used to removed damaged glass fibers and smeared epoxy resin. • Very critical step to ensure via reliability.
  11. 11. 11 Positive Etchback
  12. 12. 12 Positive Etchback
  13. 13. 13 Electroless copper plating • Electroless copper plating covers entire board, especially drilled hole walls. • Provides base for subsequent electrolytic copper.
  14. 14. 14 Electrolytic copper plating • This is the conductor layer of copper applied over the electroless copper.
  15. 15. 15 PWB Microvia Failure
  16. 16. 16 BGA Solder Joints
  17. 17. 17 Traditional Sn-Pb eutectic joints Pb free solder joints
  18. 18. 18 Head-on pillow (HoP) BGA joint HoP is caused by: •Solder paste printing and rheology issues •Reflow temperature uneven or too low •Board warping during reflow •Process out of control
  19. 19. 19
  20. 20. 20 As BGAs get smaller they can be more prone to failure
  21. 21. 21 Failure of microBGA joint
  22. 22. 22 Do Pb-free and Pb/Sn mix well?
  23. 23. 23 BGA Dye & Pry Test
  24. 24. 24 Dye & Pry Testing • This is a quick/inexpensive way to look for cracked or non-wetted BGA joints. • Allows for simultaneous inspection of all of the joints at once. • Materials and equipment needed are readily available
  25. 25. 25 Dye & Pry Test Procedure • Cut out device to be tested from the PCB • Clean flux from under device and bake dry • Immerse part in Dykem Red fluid under partial vacuum • Shake off excess dye and bake dry • Pry off BGA using pliers and/or vise and screwdriver • Inspect for any dye on separated joints
  26. 26. 26 Dye & Pry
  27. 27. 27 Post-Pry inspection
  28. 28. 28 Post-Pry inspection
  29. 29. 29 Fatigue failure of Column Grid Array (CGA) solder joints
  30. 30. 30 Flip Chip solder joints
  31. 31. 31 Flip chip cracking due to flexure
  32. 32. 32 Chip on chip with Au stud bumps
  33. 33. 33 Au-Sn lid seal voids seen at x-ray; are they for real?
  34. 34. 34 Au-Sn lid seal voids seen at x-ray; are they for real?
  35. 35. 35 These voids are real!
  36. 36. 36 Thermal Fatigue • When the assembly is temperature or power cycled the different materials in the attach want to expand/contract according to their CTE’s. • The attach material is (usually) the weakest point in the assembly so it is expected to absorb the stresses of thermal mismatch by yielding in creep. • The amount of creep an attach can endure is limited, then it will begin to crack.
  37. 37. 37 Solder fatigue in thru-hole joint
  38. 38. 38 Thermal fatigue in gull-wing joints
  39. 39. 39 Classic Solder Fatigue!
  40. 40. 40 Temp cycle failure of a BGA joint
  41. 41. 41 Black Pad failure This only occurs on Electroless Nickel, Immersion Gold (ENIG) finished devices & boards: • ENIG has come into wide use with the advent of RoHS and the lead- free solders • The ENIG process actually “corrodes” the top layer of the electroless nickel-phosphorous as the gold is deposited in a displacement reaction • This displacement reaction concentrates the phosphorous in the upper nickel layer right under the gold, and sometimes gets out of control • Normal electroless nickel will have 8-12% P, but black pad regions can have up to 30% P! • During soldering the very thin gold layer dissolves instantly leaving the solder on top of the corroded, high P, nickel layer. • This can result in dewetting and/or poor solder joint strength • When the solder joints fail, the corroded nickel layer is exposed and it is usually black in appearance; hence the name…
  42. 42. 42 Black Pad failure
  43. 43. 43 Black Pad failure
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