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PCB Design Best Practices for
More Reliable Manufacturing
Duane Benson
The Five Most Common Problems
1. Via in pad
2. QFN center pad
3. Footprints and marking
4. Thermal manufacturing issues
5....
Why These Issues?
Things that don’t matter at .1” do matter at .01”
15mm / 0.6”
1206
01005
Why These Issues?
Things that don’t matter at .1” do matter at .01”
15mm / 0.6”
1206
01005
1mm tip
Why These Issues?
Things that don’t matter at .1” do matter at .01”
15mm / 0.6”
1206
01005
0603 package 1mm tip
Why These Issues?
Things that don’t matter at
.1” do matter at .01” 2.54mm / 0.1”
0.4mm
1mm tip
Why These Issues?
Things that don’t matter at
.1” do matter at .01” 2.54mm / 0.1”
0.4mm
1mm tip
Don’t Fear the New Components
New form-factor components come
with a number of challenges, but
they can all be easily over...
FIVE COMMON TRAPS
1. VIA IN PAD
Open Via In and Near Pad
BGA
Open Via In and Near Pad
Vias in or near BGA pads will cause loss of
solder balls resulting in a failed assembly
First of ...
Open Via In and Near Pad
Vias in or near BGA pads will cause loss of
solder balls resulting in a failed assembly
2nd of al...
Open Via In and Near Pad
Vias in or near BGA pads will cause loss of
solder balls resulting in a failed assembly
3rd of al...
Open Via In and Near Pad
Just No
BGA
We salvaged this one, but don’t count on it
Open Via In and Near Pad
Filled and plated over at the board house
Copper plugs
Conductive epoxy
Thermal epoxy
The ONLY vi...
Open Via In and Near Pad
QFN, DFN, QFP may require vias in the center
pad for thermal transfer or for grounding.
Open vias...
Open Via In and Near Pad
QFN, DFN, QFP may require vias in the center
pad for thermal transfer or for grounding.
Open vias...
Open Via In and Near Pad
More options with QFN/DFN than
with BGAs. Fill, plate or cap
QFN and DFN
Open Via In and Near Pad
This may not be acceptable with immersion silver
surface finish due to corrosion. Check with fab ...
Open Via In and Near Pad
QFN and DFN
Open Via In and Near Pad
QFN and DFN
Open Via In and Near Pad
Passives & others
Insufficient solder on
pad and solder on
back side of PCB
Open Via In and Near Pad
Small components are subject to a number of
problems that don’t affect larger parts
Passives & ot...
Open Via In and Near Pad
Basically, just don’t do it.
It can lead to too many
reliability problems.
Passives & others
Insu...
FIVE COMMON TRAPS
2. QFN CENTER PAD
QFN Stencil Layer
QFN Stencil Layer
QFN/DFN solder paste stencil opening is
sensitive to a number of factors.
QFN Float
QFN Stencil Layer
QFN/DFN solder paste stencil opening is
sensitive to a number of factors.
QFN Float prevented
QFN Stencil Layer
QFN/DFN solder paste stencil opening is
sensitive to a number of factors.
QFN Voids
QFN Stencil Layer
QFN/DFN solder paste stencil opening is
sensitive to a number of factors.
QFN Voids avoided
QFN Stencil Layer
Segment the stencil so solder doesn’t
cover the capped vias.
QFN and DFN
Capped vias will
be in between ...
QFN Stencil Layer
Segment the stencil so solder doesn’t
cover the capped vias.
QFN and DFN
How not to do it
QFN Stencil Layer
QFN Stencil Layer
Stencil layer openings
segmented
Vias between the
openings
QFN and DFN
QFN Stencil Layer
Can apply to other components as well
FIVE COMMON TRAPS
3. FOOTPRINTS AND MARKINGS
Footprint and Marking
While you’re at it, make sure the
footprint matches the copper on the part
Footprint and Marking
While you’re at it, make
sure the footprint matches
the copper on the part
It’s important with thru-...
Footprint and Marking
Diode and capacitor polarity ambiguity can cause
problems in prototype and final assembly
Footprint and Marking
Diode and capacitor polarity ambiguity can cause
problems in prototype and final assembly
FIVE COMMON TRAPS
4. THERMAL MANUFACTURING ISSUES
Thermal Issues
Thermal mass of large
component can cause
uneven paste melt or
component overheating
Thermal inertia
Thermal Issues
Thermal inertia
Thermal Issues
Thermal inertia
Thermal Issues
Thermal inertia
Thermal Issues
Thermal mass of large
component can cause
uneven paste melt
Mask too thick
can cause part to
ride up and no...
Thermal Issues
Thermal mass of
larger copper area
(even internal layer)
on one side can cause
uneven paste melt
Tombstoning
Thermal Issues
No thermal relief can cause tombstoning
and poor solder joints
Thermal Issues
Meets IPC spacing
requirements
But, no mask
between parts. All
open copper (and
no thermal relief)
Thermal Issues
Meets IPC spacing
requirements Result
Thermal Issues
Meets IPC spacing, has thermal relief but
still has open copper between parts.
Thermal Issues
Meets IPC spacing, has thermal relief
and no open copper between parts.
Thermal Issues
Meets IPC spacing, has thermal relief
and no open copper between parts.
FIVE COMMON TRAPS
5. BOM EXPLOSION
BOM Explosion
Feeders may be a
limitation for
projects with large
BOMs.
BOM Explosion
R18 can be as low as 1K
If current draw isn’t an
issue, use 27K
Summary
• No open vias in pads
• Segment your QFN stencils
• Verify footprints
• Clarify polarities
• Watch for BOM line i...
blog.screamingcircuits.com
For additional layout advice
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Pcb design best practices for more reliable manufacturing

  1. 1. PCB Design Best Practices for More Reliable Manufacturing Duane Benson
  2. 2. The Five Most Common Problems 1. Via in pad 2. QFN center pad 3. Footprints and marking 4. Thermal manufacturing issues 5. BOM explosion
  3. 3. Why These Issues? Things that don’t matter at .1” do matter at .01” 15mm / 0.6” 1206 01005
  4. 4. Why These Issues? Things that don’t matter at .1” do matter at .01” 15mm / 0.6” 1206 01005 1mm tip
  5. 5. Why These Issues? Things that don’t matter at .1” do matter at .01” 15mm / 0.6” 1206 01005 0603 package 1mm tip
  6. 6. Why These Issues? Things that don’t matter at .1” do matter at .01” 2.54mm / 0.1” 0.4mm 1mm tip
  7. 7. Why These Issues? Things that don’t matter at .1” do matter at .01” 2.54mm / 0.1” 0.4mm 1mm tip
  8. 8. Don’t Fear the New Components New form-factor components come with a number of challenges, but they can all be easily overcome
  9. 9. FIVE COMMON TRAPS 1. VIA IN PAD
  10. 10. Open Via In and Near Pad BGA
  11. 11. Open Via In and Near Pad Vias in or near BGA pads will cause loss of solder balls resulting in a failed assembly First of all: No. BGA
  12. 12. Open Via In and Near Pad Vias in or near BGA pads will cause loss of solder balls resulting in a failed assembly 2nd of all: No. BGA
  13. 13. Open Via In and Near Pad Vias in or near BGA pads will cause loss of solder balls resulting in a failed assembly 3rd of all: No BGA
  14. 14. Open Via In and Near Pad Just No BGA We salvaged this one, but don’t count on it
  15. 15. Open Via In and Near Pad Filled and plated over at the board house Copper plugs Conductive epoxy Thermal epoxy The ONLY viable solution for BGA via in pad is to have the vias filled and plated over at the PCB fab house
  16. 16. Open Via In and Near Pad QFN, DFN, QFP may require vias in the center pad for thermal transfer or for grounding. Open vias are not acceptable. QFN and DFN
  17. 17. Open Via In and Near Pad QFN, DFN, QFP may require vias in the center pad for thermal transfer or for grounding. Open vias are not acceptable. QFN and DFN
  18. 18. Open Via In and Near Pad More options with QFN/DFN than with BGAs. Fill, plate or cap QFN and DFN
  19. 19. Open Via In and Near Pad This may not be acceptable with immersion silver surface finish due to corrosion. Check with fab house QFN and DFN
  20. 20. Open Via In and Near Pad QFN and DFN
  21. 21. Open Via In and Near Pad QFN and DFN
  22. 22. Open Via In and Near Pad Passives & others Insufficient solder on pad and solder on back side of PCB
  23. 23. Open Via In and Near Pad Small components are subject to a number of problems that don’t affect larger parts Passives & others
  24. 24. Open Via In and Near Pad Basically, just don’t do it. It can lead to too many reliability problems. Passives & others Insufficient solder on pad and solder on back side of PCB IPC-A-610 Class Zero
  25. 25. FIVE COMMON TRAPS 2. QFN CENTER PAD
  26. 26. QFN Stencil Layer
  27. 27. QFN Stencil Layer QFN/DFN solder paste stencil opening is sensitive to a number of factors. QFN Float
  28. 28. QFN Stencil Layer QFN/DFN solder paste stencil opening is sensitive to a number of factors. QFN Float prevented
  29. 29. QFN Stencil Layer QFN/DFN solder paste stencil opening is sensitive to a number of factors. QFN Voids
  30. 30. QFN Stencil Layer QFN/DFN solder paste stencil opening is sensitive to a number of factors. QFN Voids avoided
  31. 31. QFN Stencil Layer Segment the stencil so solder doesn’t cover the capped vias. QFN and DFN Capped vias will be in between the stencil openings Space for six vias
  32. 32. QFN Stencil Layer Segment the stencil so solder doesn’t cover the capped vias. QFN and DFN How not to do it
  33. 33. QFN Stencil Layer
  34. 34. QFN Stencil Layer Stencil layer openings segmented Vias between the openings QFN and DFN
  35. 35. QFN Stencil Layer Can apply to other components as well
  36. 36. FIVE COMMON TRAPS 3. FOOTPRINTS AND MARKINGS
  37. 37. Footprint and Marking While you’re at it, make sure the footprint matches the copper on the part
  38. 38. Footprint and Marking While you’re at it, make sure the footprint matches the copper on the part It’s important with thru- hole parts too
  39. 39. Footprint and Marking Diode and capacitor polarity ambiguity can cause problems in prototype and final assembly
  40. 40. Footprint and Marking Diode and capacitor polarity ambiguity can cause problems in prototype and final assembly
  41. 41. FIVE COMMON TRAPS 4. THERMAL MANUFACTURING ISSUES
  42. 42. Thermal Issues Thermal mass of large component can cause uneven paste melt or component overheating Thermal inertia
  43. 43. Thermal Issues Thermal inertia
  44. 44. Thermal Issues Thermal inertia
  45. 45. Thermal Issues Thermal inertia
  46. 46. Thermal Issues Thermal mass of large component can cause uneven paste melt Mask too thick can cause part to ride up and not solder well Tombstoning
  47. 47. Thermal Issues Thermal mass of larger copper area (even internal layer) on one side can cause uneven paste melt Tombstoning
  48. 48. Thermal Issues No thermal relief can cause tombstoning and poor solder joints
  49. 49. Thermal Issues Meets IPC spacing requirements But, no mask between parts. All open copper (and no thermal relief)
  50. 50. Thermal Issues Meets IPC spacing requirements Result
  51. 51. Thermal Issues Meets IPC spacing, has thermal relief but still has open copper between parts.
  52. 52. Thermal Issues Meets IPC spacing, has thermal relief and no open copper between parts.
  53. 53. Thermal Issues Meets IPC spacing, has thermal relief and no open copper between parts.
  54. 54. FIVE COMMON TRAPS 5. BOM EXPLOSION
  55. 55. BOM Explosion Feeders may be a limitation for projects with large BOMs.
  56. 56. BOM Explosion R18 can be as low as 1K If current draw isn’t an issue, use 27K
  57. 57. Summary • No open vias in pads • Segment your QFN stencils • Verify footprints • Clarify polarities • Watch for BOM line item creep
  58. 58. blog.screamingcircuits.com For additional layout advice
  • seyfeddineJERBI

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    Sep. 10, 2018
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    Mar. 28, 2017

Pcb design best practices for more reliable manufacturing

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