what is LTCC?
design rules
      
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Design Rules
Terminology Table Of Main Values Cavities/Windows


Because of the shrinking of the LTCC tapes during the firing it is very necessary to observe various design rules. This part is based on a few design guides published from the following manufacturers / processors:

  • DuPont: LTCC-Technology Design And Layout Guideline Green Tape System (EKP,12.8.1998);
  • CTS Microelectronics: Low-Temperature Cofired Ceramic Design And Layout Guidelines For The Fabrication Of Networks, Packages and Multichip Modules;
  • National Semiconductor: Design Rules For Physical Layout Of Low Temperature Co-Fired Ceramic Modules (Version_8.1);
  • Scrantom Engineering Inc.: Low Temperature Cofired Ceramic Design Guidelines (Rev. C);
  • Siegert electronic GmbH: Design Rules For LTCC (Rev. C);
  • Sorep-Erulec: General Design Guide For LTCC Substrates (8-jan-99).

All called numbers are average values and ranges and may vary from one to the other system; these rules depend on both material and process properties. This paper doesn't intend to describe all known design rules; it should only give an idea about the possibilities of LTCCs.


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Terminology

1 : Top Side External Conductor
2 : Cofired or Postfired Surface Resistor
3 : Buried Resistor
4 : Buried Via
5 : Buried Capacitor
6 : Stacked Vias
7 : Blind Via
A : Via Cover Pad
B : Via Diameter
C : Via Stagger
D : Via Spacing
E : Via Pitch
F : Via Center To Part Edge
A : Line Pitch
B : Line Spacing
C : Line Width
D : Conductor To Part Edge / Edge To Feature
E : Via To Conductor Line Spacing
F : Via Center To Part Edge
G : Line To Cavity Wall Spacing
H : Cavity Size
I : Cavity Wall To Part Edge Spacing


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Table Of Main Values

Standard Possible
Edge To Feature in um 500 250
Line Width in um 200 100
Line Width in um (Fine Line Process) 50 50
Line Spacing in um 200 100
Line Spacing in um (Fine Line Process) 50 50
Line Pitch in um 400 200
Line To Cavity Wall Spacing in um 400 /
Via Diameter in um 250 100
Via Coverpad / Catchpad 2x via diameter via diam. 25um
Via Spacing in um 200 175
Via Pitch in um 400 300
Via Stagger 1.5x via diameter /
Via To Cavity Wall Spacing in um 550 300
Via Geometry Round + Rectangular Round + Rectangular
Via Types blind, buried, stacked blind, buried, stacked
Thermal Via Coverage in % 15 30
Min. Resistor Dimensions in mm 1 x 1 0.5 x 0.5
Min. Resistor Overlap in um 300 200
Min. Width After Trimming in um 300 200
Tolerance After Trimming (Surface / Buried) +/- 2% / +/- 25% +/- 1% / x
Ground / Power Plane Coverage 50% 75%
Opening For Feed Through (length in um) 750 350
Max. Number Of Layers Depends on Thickness (10 - 50) Depends on Thickness (10 - 50)
Min. Number Of Layers Depends on Thickness (2 - 4) Depends on Thickness (2 - 4)
Circuit Shapes Rectangular, special shapes possible Rectangular, special shapes possible
Size Tolerance +/- 0.5% +/- 0.25%
Cavity's Shape Rectangular, circular, special shapes possible Rectangular, circular, special shapes possible
Min. Floor Thickness in um 450 200
Max. Cavity Depth in um 1500 2500
Min Cavity Size in um 1000 500
Max. Cavity Size in um Depends on layout Depends on layout
Cavity Wall To Part Edge Spacing in um >1000 /
Bond Pad / Conductor Discoverage in um 750 /
Cavity Wall To Conductor Spacing in um 400 /
Cavity Wall To Via Spacing in um 2.5x via size /
Cavity Wall To Pad Spacing in um 250 /
Spacing Between Two Cavities in um 1270 /
Window's Shape Rectangular, circular, special shapes possible Rectangular, circular, special shapes possible
Window Depth in um < 2000 > 2000
Min. Window Size (length in um) 1000 500
Max. Window Size (length in um) Depends on layout Depends on layout
Pitch Of BGA / LGA I/Os in mm 2.54 0.635
Wire Bonding Pitch in um 500 150
Solder Pad Pitch in um 400 250
Flip Chip Bonding Pitch in um 400 250

A : Bond Pad / Conductor Discoverage
B : Cavity Wall To Bond Pad Spacing
C : Cavity Wall To Conductor spacing
D : Cavity Wall To Via Spacing
E : Cavity Wall To Die Pad / Bottom Conductor Spacing


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Cavities / Windows

Cavities are openings in the ceramic through a various number of layers with a bottom; windows are openings through the hole ceramic without a bottom.


Standard Possible
Cavity's Shape Rectangular, circular, special shapes possible Rectangular, circular, special shapes possible
Min. Floor Thickness in um 450 200
Max. Cavity Depth in um 1500 2500
Min Cavity Size in um 1000 500
Max. Cavity Size in um Depends on layout Depends on layout
Cavity Wall To Part Edge Spacing in um >1000 /
Cavity Wall To Bond Pad Spac. in um (B) 250 /
Bond Pad / Conductor Discover. in um (A) 750 /
Cavity Wall To Conductor Spac. in um (C) 400 /
Cavity Wall To Via Spacing in um (D) 2.5x via size /
Cavity Wall To Pad Spacing in um (E) 250 /
Spacing Between Two Cavities in um 1270 /


Note:
  • If cavities need to be processed it is advisable to use an isostatic press for lamination;
  • Deep cavities need to have inlays during lamination.


Standard Possible
Window's Shape Rectangular, circular, special shapes possible Rectangular, circular, special shapes possible
Window Depth in um < 2000 > 2000
Min. Window Size in um 1000 500
Max. Window Size in um Depends on layout Depends on layout
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