High-Volume HDI PCB Manufacturing

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The power of HDI

The rise in demand for compact devices where the form factor is a major concern has led to the increase in manufacturing high-density interconnects. These boards are a part of your lifestyle gadgets like wearables, smartphones, and life-saving medtech equipment.

Fabricating HDI PCBs is a challenging task as it includes fine line width (less than 4 mils), thin dielectrics, controlled impedance, blind, buried, and microvias. These features allow devices to shrink in size. This miniaturization trend has challenged manufacturers to fit more functionalities into tiny board areas.

What are the main hurdles with HDI boards?

HDI boards should be designed to maximize component density, provide efficient breakout/fanout for ICs, and transmit high-frequency signals without reflections. The ultimate goal is to integrate greater capabilities into a small package. Some of the ways of achieving this include reducing the trace width and size of the vias. This eventually increases the routing area, thereby reducing the required number of layers and the overall size of the board.

Microvias and buried vias are incorporated into circuit boards using a technique called sequential lamination. It involves building up the PCB sequentially by laminating the subparts composed of copper and dielectric layers. One of the major challenges in this process is limiting the number of lamination cycles.

The advancement of HDI technologies has now made its way to microelectronics, where fine lines, less than 1.5 mils, can be additively placed on PCBs. In contrast, traces on the conventional high-density interconnects are formed using a subtractive process (etching of copper).

As a designer, it is very important to optimize your design based on your manufacturer’s capabilities. Adhering to the guidelines of your fab house can greatly reduce the product turn time and cost.

The fabrication of HDI boards demands skilled teams and cutting edge technologies, such as sequential lamination, laser drills, and laser direct imaging. In addition to this, your coordination with your CM plays an important role to build an efficient and reliable product.

Capabilites Overview

  • Up to 30 layers
  • Board thickness: .007″
  • Core thickness: .002”
  • Max laser aspect ratio: >.75:1
  • Bow & twist tolerance: <7% 
  • Conductive filled vias
  • Minimum pad size: .004”

Special HDI features

  • Blind, buried and microvias 
  • Up to 3 sequential laminations 
  • High-signal performance 
  • Considerations 
  • Laser direct imaging 
  • Metal-core 
  • Flex / rigid-flex

Certifications

  • ITAR 
  • IPC 6012 class 1, 2 & 3 
  • AS9100D 
  • NADCAP 
  • MIL-PRF-55110 
  • MIL-PRF-31032/1 
  • MIL-PRF-31032/2 
  • ISO 9001:2015
Via capabilities for HDI PCBs
Via Type Via parameter Sierra Electrotek capability
Blind Via Min total pad size 4 mils (.102 mm) over drill size
Min laser drill size 4 mils (.102 mm)
Mechanically drilled annular ring 4 mils (.102 mm) over drill size
Dielectric material thickness 2 mils (.051 mm)
Capture pad size 4 mils (.102 mm) over drill size
Laser aspect ratio .75:1
Buried Via Min total pad size 5 mils (.127 mm) over drill size
Min drill size 6 mils (.152 mm) – depending on aspect ration
Capture pad size 5 mils (.127 mm) over drill size
Laser aspect ratio .75:1
Through Hole Min total pad size 5 mils (.127 mm) over drill size
Min drill size 6 mils (.152 mm)
Capture pad size 5 mils (.127 mm) over drill size
Max layer count 26+
Min finish thickness .01″ (.254 mm)
Min trace width (I/L) 3 mils (.076 mm)
Min trace width (O/L) 3 mils (.076 mm)
Min space width (I/L) 3 mils (.076 mm)
Min space width (O/L) 3 mils (.076 mm)
Max lamination cycles 4
Min hole size 6 mils (.152 mm)
Min pitch .157″ (.4 mm)
Stacked vias Yes
Staggered vias Yes
Conductive filled vias Yes
Non-conductive filled vias Yes
Copper plate shut microvias Yes
Heat sinks Yes
UL 94V-0 (on selected materials) Yes
Quality reports for HDI PCBs
Report type Sierra Electrotek capability
Specifications IPC-6012, class 1, 2, 3, & ES Yes
IPC-6013, class 1, 2 & 3 Yes
31032 MIL-PRF-55110 (on selected materials) Yes
Reports / Certificates Micro section Yes
Solderability Yes
X-ray fluorescence No
Ionic contamination Yes
Time domain reflectometry (TDR) Yes
First article inspection (FAI) Yes
Certificate of compliance (C of C) Yes
Electrical test Yes
Fabrication parameters for HDI PCBs
Fabrication parameter Sierra Electrotek capability
Panel sizes 14×26″ (36×66 cm), 21×25″ (53×64 cm), 21x 29″ (53×74 cm), 12×18″ (30×46 cm), 18×24″ (46×61 cm), 16×18″ (41×46 cm)
Min board thickness .007″ (.178 mm)
Max board thickness .25″ (6.4 mm)
Thickness tolerance <10%
Bow & twist tolerance < 7%
Min core thickness .002″ (0.51 mm)
Min dielectric .002″ (.051 mm)
Min starting copper foil weight 9 micron (.009 mm)
Preferred materials for HDI PCBs
Material Type Raw board manufacturer Sierra Electrotek capability
FR-4 Lead Free Isola 370 HR Yes
Ventec VT47 Yes
Nan Ya NPG-170 Yes
Polyimide Isola P95 Yes
Nelco N7000-2 HT Yes
Arlon 85N Yes
Highspeed FR/MW Applications Isola I-speed Yes
FR 408HRR Yes
Nelco N4000-13 Yes
Nelco N4800-20 Yes
Teflon Nelco N9000-13 RF Yes
Rogers RO3000 Series Yes
Rogers RT/DUROID Series Yes
Rogers ULTRALAM 2000 Yes
Ceramic Rogers RO4003 Yes
Rogers RO4350 Yes
Rogers TTM 3, 4, 6, 10, 10i Yes
Taconics CER-10 Yes
Taconics RF-35, RF-35A2 Yes
Taconics RF-60 Yes
Flex DuPont Pyralux AP Yes
DuPont Pyralux LF Yes
DuPont Pyralux FR Yes
Rigid Laird IMPCB Yes
Drill parameters for HDI PCBs
Drill parameter Sierra Electrotek capability
Smallest laser drill diameter .003″ (.076 mm)
Largest laser drill diameter .010″ (.254 mm)
Max laser aspect ratio >.75:1
Min mechanical diameter .005″ (.127 mm)
Max mechanical aspect ratio > 10:1
Min mechanical drill to copper .005″ (.127 mm)
Min plated through hole tolerance +/- .002” (.051 mm)
Min non plated through hole tolerance +/- .001” (.025 mm)
Pad diameter parameters for HDI PCBs
Board Type Placement Sierra Electrotek capability
Rigid Inner layer Drill + .008″ (.203 mm) + class 2
Outer layer Drill + .006″ (.152 mm) + class 2
Flex Inner layer Drill + .010″ (.254 mm) + class 2
Outer layer Drill + .008″ (.203 mm) + class 2
Conductor parameters for HDI PCBs
Feature Conductor parameter Sierra Electrotek capability
Pad Size Min pad size for electrical test .004″ (.102 mm)
Min wire bond pad size .004″ (.102 mm)
Min Trace Vs Copper Thickness Note: Thickness includes starting foil plus panel plates (for wrap if any) to beetched. 5 microns .002″ (.051 mm)
9 microns .0025″ (.064 mm)
3/8 oz .003″ (.076 mm)
1/2 oz .0035″ (.089 mm)
1 oz .0045″ (.114 mm)
2 oz .006″ (.152 mm)
3 oz .0065″ (.165 mm)
> 3 oz Contact us
Min Space Vs Copper Thickness Note: Thickness includes starting foil plus panel plates (for wrap if any) to beetched. 5 microns .0025″ (.064 mm)
9 microns .003″ (.076 mm)
3/8 oz .0035″ (.089 mm)
1/2 oz .004″ (.102 mm)
1 oz .005″ (.126 mm)
2 oz .0065″ (.165 mm)
3 oz .007″ (.178 mm)
> 3 oz Contact us
Permanent solder mask parameters for HDI PCBs
Type Solder mask parameter Sierra Electrotek capability
Liquid Photoimageable (LPI) Colors Green, red, blue, yellow
Gloss Semi-gloss, matte (only in green)
Min dam/web size SMT .004″ (.102 mm)
Min dam/web size BGA .0035″ (0.89 mm)
Clearance >.0005″ (.013 mm)
Mask-defined SMT Or BGA (not ground plane) Yes
Mask-defined features on ground plane Yes
Laser Direct Imaging (LDI) Colors Green, black, red, blue
Gloss Semi-gloss
Min web for SMT .004″ (.102 mm)
Min web for BGA .0035″ (.089 mm)
Clearance .005″ (.126 mm)
Mask-defined SMT Or BGA (not ground plane) Yes
Nelco N7000-2 Yes Yes Yes
Hi Pot No Yes Yes
No Flow Prepreg Yes Yes Yes
Panasonic Megtron Yes Yes Yes
Panasonic R1755 Yes Yes No
Panasonic R1766 Yes Yes Yes
Polyclad Getek Yes Yes Yes
PSA Bond Film No Yes Yes
Rogers 3000 Series Yes Yes No
Rogers R4000 Series Yes Yes No
Rogers 5000 Series Yes Yes No
Rogers 6000 Series Yes Yes No
Rogers TMM Yes Yes No
Ventec VT47 Yes No No
Legend mask parameters for HDI PCBs
Type Legend mask parameter Sierra Electrotek capability
Sprint Color White
Min line .050″ (1.27 mm)
Min height .025″ (.635 mm)
Screen Printable Colors White, yellow, black, red
Min line .007″ (.178 mm)
Min height .030″ (.762 mm)
Surface finishes for HDI PCBs
Surface finish Sierra Electrotek capability
HASL (vertical & horizontal) Yes
Lead free HASL Yes
OSP (Shikoku F2 & Entek) Yes
ENIG (electroless nickel / immersion gold) Yes
ENEPIG (electroless nickel-electroless paladium-immersion gold) Yes
Immersion silver Yes
Tin nickel No
Electrolytic soft gold Yes
Electrolytic hard gold Yes
Fabrication parameters for HDI PCBs
Fabrication parameter Sierra Electrotek capability
Mechanical Min route cutter available .021″ (.533 mm)
Routed part size tolerance <.010″ (.254 mm)
Counter sink Yes
Counter bore Yes
Bevel angles 20, 30, 45
Laser Milling, depth tolerance +/- .003″ (.076 mm)
Laser routed thickness <.032″ (.813 mm) thick
Routed array Yes
V Score Angles 30, 45, 60
Edge to copper .007″ (.178 mm)
Dicing Edge to copper .005″ (.127 mm)
Edge / Castellation Min drill via .010″ (.254 mm)
Edge plating Yes
Other screenable materials for HDI PCBs
Screenable material Sierra Electrotek capability
Carbon ink Yes
Peelable solder mask Yes
Electrical tests available for HDI PCBs
Report type Sierra Electrotek capability
Controlled impedance 5% w/ F/A
Hi pot Yes
Test voltage 40, 250, 500
Isolation resistance (Mohms) >100
>100 <.010
Min pad size .004″ (.102 mm)