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1 EAT – E-learning Module 3. Printed wiring boards 3.1 Types and materials of printed wiring boards Department of Electronics Technology Budapest University.

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Presentation on theme: "1 EAT – E-learning Module 3. Printed wiring boards 3.1 Types and materials of printed wiring boards Department of Electronics Technology Budapest University."— Presentation transcript:

1 1 EAT – E-learning Module 3. Printed wiring boards 3.1 Types and materials of printed wiring boards Department of Electronics Technology Budapest University of Technology and Economics BME-ETT Elect2eat Team:Zsolt Illyefalvi-Vitéz, PhD www.ett.bme.huOlivér Krammer János Pinkola, dr

2 2 The Printed Wiring Board (PWB) A printed wiring board (or PWB) is used to mechanically support and electrically connect electronic components using conductive pathways, or traces, etched from copper sheets laminated onto a non-conductive substrate.

3 3 Types and materials of printed wiring boards Cu layer: 17, 35, 70, (105) µm Substrate (v): 0,2….3,2 mm Cu wire Fiberglass layer epoxy Functions: Electric connection between component leads Fixing components mechanically Printed wiring: Wiring made on resin based insulating board (foil, surface) Conductive layer is mainly copper Substrate (base material): Copper foil covered, reinforced resin v Insulating substrate Cu layer A Printed Wiring Board (PWB) is a substrate, which is made up of an insulating board with copper foil tracks on its outer surfaces.

4 4 PWB categories according to the layer structure one sided double sided multilayer metal substrate metal core 3D, MID (Molded Interconnect Device) multiwire

5 5 PWB categories according to types and materials For circuit cards and modules the rigid printed wiring boards are used, while flexible and rigid-flex printed wirings are popular for the interconnection of cards placed in different position in equipment or of different modules and units. Rigid printed wiring boardFlexible printed wiring board Rigid  - Reinforcing material (paper, fiberglass, polyaramide, metal…) - Resin (phenol, epoxy, polyimide, PTFE…) Flexible  (polyester, polyimide, PTFE)

6 6 Characteristics of PWB substrates FR flame retardant CEMComposite Epoxy Material: Cu fiberglass epoxy paper

7 7 PWB categories according to pattern resolution Normal Fine Very fine Through-hole mounted: SMT, COB, MCM-L:

8 8 electrical connection between certain conducting layers more reliable soldered joints when using through-hole mounted components Aim of the through-hole metallization Through- hole with metallized wall

9 9 delamination Typical through-hole failures barrel crack corner crack pad rotation missing plating pad lifting nodule pull away break between layer and plating plating void misalignment of PCB during drilling imprecise fitting

10 10 3. Printed wiring boards 3.2 Mechanical technologies in PWB-production

11 11 Mechanical technologies in PWB-production 1.Hole formulation – punching: Ø > 1,0 mm, FR2, FR3 – drilling: Ø > 0,1 mm, FR4... – laser-, photo-, plasmavia: Ø 0,05…0,2 mm 2.Brushing 3.Milling (routing) 4.(Pressing) 1. Hole formulation a) Punching The shape is formed by pressing the material against a die with a huge force The shear forces generated between the material and die separate the material into the desired shape Removal of material by the relative movement of the tool and the workpiece

12 12 b) Drilling Primary movement: rotation of drill → cutting speed (v, m/min) Secondary movement: perpendicular to the surface → feedrate (f, mm/rot.) the material of workpiece the material of tool and it's geometry the speed components of relative movement (main- and side movements) Dominant factors: Composition: Mechanical technologies in PWB-production 88...94 % tungsten carbide (WC) 6...12 % cobalt (Co)

13 13 Drill package formulation Entry plate: preventing of abrasion preventing of burring increase of hole position accuracy increase of hole wall quality Backup plate: preventing of burring protecting of CNC working table Entry plate Backup plate Hole Substrates Mechanical technologies in PWB-production

14 14 c) Drilling by UV laser Laser micro-hole drilling can be used to produce micro- holes in almost any material. Very high position and diameter tolerances can be achieved. 1. step 2. step Removing Cu Removing organic with high intensity with low intensity Cleaned and coarsed copper surface d) Plasma etching High voltage, high energy, rapid rise time electrical pulses are delivered many times per second to an electrode assembly in contact with the material body to generate therein elongate plasma channels which expand rapidly following electrical breakdown of the material causing the material to fracture and fragment. Mechanical technologies in PWB-production

15 15 2. Brushing The brushing mashine contains rotating brushes with various corning and a conveyor system for feeding the board into them. For better efficiency the boards are continuously washed by water spraying 3. Milling (routing) In contrast to drilling, where the drill is moved exclusively along its axis, the milling operation involves movement of the rotating cutter sideways as well Milling is the process of cutting away material by feeding a workpiece past a rotating multiple tooth cutter Mechanical technologies in PWB-production Click on the figure to start movie!

16 16 3. Printed wiring boards 3.3 Chemical technologies in PWB-production

17 17 Chemical technologies in PWB-production The chemical technologies include the cleaning, layer deposition, layer removal, surface finishing and rinsing processes. The most important electrochemical and electroless layer deposition processes are based on the same principle: on reduction. Me n+ + ne - = Me (reduction) 1. Electroplating + _ Me n+ Can be applied only onto conductive surfaces, for selective coatings it is not suitable.

18 18 2. electroless deposition 3. „direct plating” after deposition of conductive chemical compound onto the insulator surface it can be electroplated 4. immersion deposition Me1 n+ Me2 - for catalytic insulators - purpose is to metallize the isolating wall of drilled holes Me n+ + reducing material = Me e.g. CuSO 4 + 4NaOH + 2HCHO = Cu+2HCOONa + Na 2 SO 4 + H 2 + 2H 2 O Chemical technologies in PWB-production

19 19 3. Printed wiring boards 3.4 Patterning processes of PWBs: Masking technologies

20 20 Masking technologies 1.Screen printing For patterning (or imaging) with a mask, the dry film photoresist method is the most popular in the PWB industry. Alternatively, the less expensive but lower resolution screen printing imaging technology can be used. Screen printing is the main imaging process used for solder resists, as well.

21 21 Masking technologies Photoresist applied onto Cu foil, exposed to light and developed Cu-layer Photoresist Cu-layer Photoresist 3.step: Developing dry film photoresist 2.Dry film photoresist technology 2.step: Photoresist exposure 1. step: Lamination

22 22 3. Printed wiring boards 3.5 Fabrication of single sided boards using subtractive or additive technology

23 23 Processing possibilities: Subtractive technology The raw material is a dielectric plate with copper cladding on one or both sides. The copper layer is removed (usually by chemical etching) where the wiring is not needed. The resolution is limited by the adhesion of the conducting layer and the undercutting effect. Additive technology The conducting layer is deposited on the insulating substrate in a particular pattern using a mask. It results in finer resolution but worse adhesion. Semi-additive technology It combines the advantages of both previous technologies Fabrication of single sided boards using subtractive or additive technology

24 24 The subtractive and additive technologies SubtractiveAdditive Cu foil covered insulating boardInsulating board Electroless metallization, Positive mask (screenprinting, photoresist, metal) Negative mask (screenprinting, photoresist) Etching, mask stripping Electroless metallization, mask stripping

25 25 Subtractive technology of single sided PWBs Base material: copper foil covered insulating board Undercutting Mushroom effect Mask removal [Removing metal mask („orange effect”)] Negative mask (photoresist, screen printing) Positive mask (photoresist, screen printing) Etching Positive metal mask (Sn, Sn/Pb…) Etching Solder mask wire pad

26 26 3. Printed wiring boards 3.6 Subtractive technology of double sided, through- hole metallized boards

27 27 Subtractive technology of double sided, through-hole metallized boards

28 28 The subtractive and additive technologies I. Subtractive Additive

29 29 Electroless copper The subtractive and additive technologies II. Subtractive Additive Sn plating Sn reflow

30 30 Semi-additive technology A possible way of producing the substrate

31 31 3. Printed wiring boards 3.7 Technology of co-laminated multilayer printed wiring boards

32 32 Technology of co-laminated multilayer printed wiring boards Each inner layer must be patterned and the surface of the Cu must be prepared for gluing (Sn stripping if necessary, oxidization) The inner boards can have through holes that will become buried vias in the multilayer board. Co-lamination technology: the boards are glued together with preimpregnated (prepreg) B-stage epoxy foil. Needs at least 30...60 minutes on 170 oC, at 150 N/cm2 pressure.

33 33 Cu plating Sn/Pb plating resist stripping Cu etching Technology of multilayer boards II.

34 34 Via types and layers of multilayer boards

35 35 Sequential technology with wall-metallized vias Sequential build-up (SBU) technology: A multilayer board is created by applying conductive and insulating layers one after each other.

36 36 Sequential build up (SBU) technology Comparison of structure of different microvias Laser Plasma Drilling

37 37 3. Printed wiring boards 3.8 Special printed wiring boards and their technologies

38 38 Technology of Metal Substrate PWB-s Metal core covered with insulating layer and a copper foil on the outer surface. Aim: to achieve better heat conductivity epoxy-woven fiber glass board: 0.2 W/mK, IMS boards: 1.3 W/mK. IMS = Insulated Metal Substrate Formulation of the pattern by subtractive technology: drilling of the metal plate, filling the hole with epoxy enriched with Al 2 O 3, drilling of the epoxy, metallization of the holes

39 39 Aim: to minimize the thermal expansion mismatch between the substrate and the components / to adjust the thermal expansion coefficient of the substrate to that of the components Thermal expansion coefficient: epoxy-woven fiberglass 12..16 ppm/°C CCC encapsulation 5.9…7.4 ppm/°C Metal Core PWB CCC = Ceramic Chip Carrier V=0.12..1.5 mm Core materials (  5 ppm/°C): Cu-Mo-Cu (CMC) Cu-Invar-Cu (CIC)

40 40 Flexible PWBs Two possible ways of manufacturing: 1. Cu foil laminated onto the plastic, 2. Plastic is deposited onto the Cu foil(the more up-to-date technology). Materials: plastic (polyimide - Kapton, polyester - Mylar, PTFE - Teflon) foil without rreinforcement Available in single-, double- and multilayer construction as well. Application: connecting moving elements, vibration tolerating devices (due to smaller mass), 3D interconnection systems.

41 41 Rigid-flex combined PWB Adhesive foil Wiring pattern Metallized holes Metallized through holes Flexible substrate Rigid substrate

42 42 3D MIDs (Molded Interconnection Devices) Interconnection is produced by applying the wiring onto the surface of the plastic devices. Metallization of the plastic: electroless Cu deposition. Applying the photoresist: by electrophoresis Exposure: direct writing by laser exposure applying of 3D fotomask The 3D wiring may replace some mechanical components, like touch switch components SMD Shock resistant plastic, e.g. PEI=polyetherimid

43 43 Multiwire PWB Multiwire PWB: combining the PWB technology with the conventional wiring. Metallised through holes are made after sticking insulation covered wires into the cover prepreg film.


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