Back board routing topology included Centralized Switching,Distributed Switching,Hybrid Switching,Holst/Slave Switching.
Centralized Switching
Distributed Switching
Hybrid Switching
Host/Slave Switching
The Structure of Back Board
VITA standard required the dimension of back board,tooling hole position and size,direction,each solt,and case heat dissipation etc.
Back Board Connector
Back Board use MULTIGIG RT connector,the pin of connector includes power, single signal,differential signal.the speed of differential is 10Gbps.
Back Board stack up design
Follow the signal speed to choose material. Design PCB stack up according board thickness and impedance requirement.For example: VPX Back Board, use TU-752 material,4mm board thickness,18 Layers, Layer stack up like below:
Layout Rule
Back board layout is BUS layout,each group trace don’t across and smooth. Highlight each BUS is better for planing.
Equate length
For high speed differential trace,required trace equate length.
Power Design
The main power +12V,+5V,ensure current is adequate when design.
Anti-Pad design
For the vias of certain layer stack up,impact impedance factors includes vias size,pad size, anti-pad size, Stub length,ground vias position etc.
The high in difference of heavy copper PCB is easy lead to oil float away,fake copper exposure,oil uneven when printed solder mask if controlled unwell.This article analysed and improved this problem through line mask printing area, solder mask opening of silkscreen ,printing lay up time and printing method.
Oil wrinkle: as the difference in high is big lead to oil thickness is heavy between copper and base material, heavy oil is easy to wrinkle.
Oil bubble: The air bubble is hard to squeeze out as heavy oil, produce oil bubble after pre-baking.
Long time process: overlong lay up after printing is easy let oil moist and impact reliability.
Technology and Reliability
Evaluated Technology: occured above questions as the big altitude difference,oil piled up too heavy, whether can squeeze out bubble at lay up process,reduce lay up time,we improved the technology process as below:
Through improved the process,we can save produce time 3-4hours.Put boards into vacuum machine and squeeze out air bubble can complete solve the solder mask bubble problem.
Quality is acceptable after vacuum squeezed bubble.
Through improvement of the process, it save produce time 3-4hrs and simplified process,improved quality,enhanced productivity,reduce cost,improved the delivery and competitive capacity.
More PCB technology knowledge please contact: info@kingsunpcb.com.
Vias is the important constitute of PCB, the cost of drilling fee is 30%-40% of whole PCB cost.
Parasitic capacity of vias
The parasitic capacity exists in vias refer to ground layer. Assume ground layer isolate via diameter is D2, via pad diameter is D1, PCB thickness is T, dielectric constant is ε, then vias parasitic capacity is: C=1.41ε TD1/(D2-D1) ,Vias parasitic impact the time of transmission up., slow the speed of circuit.E.g. PCB with 50mil thickness,if the via diameter is 10mil and pad diameter is 20mil,The distance between pad and ground copper is 32mil, then we can calculates parasitic capacity is: C=1.41×4.4×0.050×0.020/(0.032-0.020)=0.517pf, the time change of parasitic capacity is: T10-90=2.2C(Z0/2)=2X0.517X(55/2)=31.28ps. From the data we can see one single via is not big impact for transmission. But if there have many vias in board, the impact is huge,so design enginner should be consider this situation.
Parasitic inductance of vias
The parasitic inductance is also exists in vias,in high-speed circuit design,the endanger of parasitic inductance is more than parasitic capacity.its parasitic serics inductance will down shunt capacity contribution,weaken filter action of whole power system. We can calculate a vias parasitic inductance use the formula: L=5.08h｛In(4h/d)+1｝,L is the inductance,h is the vias length,d is the via diameter.we can see the via’s diameter is small impact for the inductance in the formula. The via’s length is big impact for the inductance. We calculate via’s inductance follow above data: L=5.08×0.050｛In(4×0.050/0.010)+1｝=1.015nH. If the signal time is 1ns,then impedance is:XL=πL/T10-90=3.19Ω, such impedance can’t be ignore in high speed circuit.Especially there need two vias for one shunt capacity,so the parasitic inductance will fold increase.
Vias layout in high-speed PCB
After above analysed,we can see vias will bring negative impacts in high-speed circuit design. We can follow below rules for avoid the via’s negative impacts.
(a. ) Consider from cost and signal quality, choose suitable via size. It’s better set 10/20mil of drill/pad for 6~10 Layer PCB. For high density and small dimension,also can try 8/18mil vias.it can be considered large vias for power and ground trace to reduce impedance.
(b. ) From above two formulas,we can see thin PCB in favor of reduce parasitic capacity and inductance.
(c. ) Vias near power and ground components is as close as possible to components,the same time power and ground trace try get short and large to reduce impedance.
(d. ) Signal trace don’t change layer if unnecessary,means don’t set redundant vias.
(e. ) Set some vias near the vias of signal trace so that it can provide return circuit for signal. More vias can be set in ground layer. Above vias module we discussed under exist pad in every layer. Sometimes, we can decrease the pads size or delete them.Especially under vias density is big, it may lead to break slot of break return circuit in copper layer. We need decrease the pad size of these vias or move vias position to solve the question.
More PCB Technology please contact us: info@kingsunpcb.com.
If you open SOC PCB Layout Guide,you can see it mentions high speed signal line’s angle question: high speed signal line don’t layout in right-angle, it should layout in 45 degree angle,and arc is better then 45 degree. How’s the truth? How to design the circuit line? 45 degree or 90 degree? let’s discuss in this article.
PCB line corner can be acute angle?
Rules of thumb PCB line corner can’t be acute angle.Follow PCB DFM,If lines corner are acute angle,it will easy appears acid traps problem.then lead to line over-etched when etching process.Despite PCB manufacture engineer will check and fill the acid traps, but it risks signal integrity question.thus we should avoid this problem at PCB layout process.Using the Enhanced Pad Entry tool can avoid acute angle between trace and pad at layout,avoid acid traps questions.Using toggle option can avoid acid traps of acute angle at Cadence Allegro layout.PCB line corner can be 90 degree
High-speed signal trace should avoid 90 degree,because impedance trace required width is accordance from beginning to end. If trace is 90 degree will lead to signal trace transmission delay.Follow article”Right angle corners on printed circuit board traces,time and frequency domain analysis” and”Who’s Afraid of the Big Bad Bend?”, we can get below conclusion: 90 degree can effect signal trace for high speed signal PCB. Trace 4-5mil, 90 degree capacity with 10ft,after tested,it delay 0.25ps as capacity. So 5mil trace and 90 degree is not very big influence.PCB line corner can be 45 degree
We use 45 degree in general except frequency signal and other special signals. The corner line length should be 1.5 time of trace width when line walk long. Space between trace to should be 4 times of width.PCB line corner can be arc
We think lines are not necessary to be arc if not microwave transmission or other special requirement. Arc trace occupy much space and it don’t adapt to repair at later period.
Art is good for RF microwave signal transmission trace.
Follow electronics technology development,many PCBs outline became more and more complexity. New products on market require PCB outline with high accurate,also appearance is criticized.it’s difficult for traditional outline manufacture. As Laser machining have advantages like high accurate,high speed,low cost.more and more PCB manufacturers start to purchase laser equipment to solve this situation.
CO2 laser working theory
CO2 Laser used in PCB manufacture is 10.6um wavelength with high power impulse laser, it has strong ability in cutting.now CO2 laser widely used in blind via drilling,FPC outline and laser target.
Laser drilling for blind vias
Laser cut coverlay
You can see most of CO2 laser used in thin board manufacture at present.Evoke us rethink if CO2 laser can used in other manufacture range. How to expand its application to achievement from dot to line to plane? It became a major topic of common thinking in electronic industry.
CO2 laser principle of work and analysis
CO2 laser work is dot matrix from dot to line.when the space between dot and next is enough small,laser appears smooth cutting like below：
look at the front horizontal of laser cutting:
Actual picture of look at the front horizontal of laser cutting
Overhead view of laser cutting
Actual picture of Overhead view of laser cutting
As laser cutting focal distance is limited,laser power will reduce follow the depth increase, like v-cut theory. As laser beam is small,so the cutting edge is small,the cross-section like below:
cross-section sketch:
The actual cross-section picture:
CO2 Laser plane cutting principle and analysis:
Laser plane connects 3 dimension,dot-matrix picture is 2 dimension, and laser power decide the 3rd dimension. Dot- matrix design follow beam dimension to calculate,overspread whole panel,can meet different depth of cutting.
Doc-matrix cutting,it will appears micro-pit.we need adjust the laser power,make the depth of cutting don’t effect by micro-pit, it almost smooth in appearance.
CO2 laser fabrication application and technology development
PCB material of laser cutting effect analysis
CO2 laser always used in nonmetal material,as the absorbance of laser is high to nonmetal materials.we analyse several common materials of resin+ glass epoxy,PTEE+glass+ceramics filler’s laser cutting effects and study laser cutting quality and manufacture control.we study from three aspects, the first aspect is laser manufacture productivity,same parameters data to compare. The second aspect is manufacture homogeneity, the highest deviation to compare. The third aspect is appearance quality,if serious carbonize after fabrication. Below is the data of comparison.
Form above manufacture results,we can see PTFE+glass it easy to laser manufacture. The highest deviation is less 0.1mm,means laser cutting can meet the outline tolerance. Resin+epoxy glass is easy carbonize in appearance,glass+ceramics is also have sligh carbonize,but PTFE+glass didn’t be carbonized.we should control this kind of carbonized problem if appearance is critical.
CO2 laser manufacture technology and development
We use laser to cut the PI coverlay and FPC outline in general. Actually laser also can use in rigid PCB,and have strong control for depth milling,so laser have big space in different material cutting.
(a.)Flex-Rigid PCB laser cutting technology
Flex-rigid PCB use V-CUT to cut the cover.Actually laser also adapt in cover cutting.it have strong control for the depth.
Compare traditional v-cut manufacture,laser can meet small depth v-cut. Common v-cut machine is limited board thickness and hardness, it’s hard manufacture small depth v-cut and thin board.
laser cutting don’t need two sides cutting,it can from one side cut to bottom side and don’t need enlarge.
Mechanical V-CUT from two sides:
Laser V-CUT from one side:
(b.) PTFE laser cutting
PTFE outline routing have more burrs use mechanical milling,rework consume much time.but no burrs if use laser routing.
But the PTFE material is more thick than PI, it over the focal distance range. So we need routing the outline from top and bottom sides.
Mechanical routing
Laser routing
CO2 Laser plane manufacture and application
(a.) PCB material’s laser plane manufacture study
Like above from different aspects to study: laser plane manufacture productivity, homogeneity and appearance.
From above results,we can see PTFE+glass’s manufacture productivity is the best.the highest deviation of homogeneity is less than 0.1mm,plane manufacture of laser can meet the tolerance.Resin epoxy+glass have serious carbonized in appearance,others don’t have this kind of problem.
(b.)Laser plane manufacture can used to rework of solder mask opening.
Sometimes board missed one pad solder mask opening after finished board,at last we had to scrap the PCB. Actually,laser machine can solve this problem so easy. Use laser make depth milling can rework the mistake very soon.
Below a pad missed solder mask opening
After laser milling
(c.) Laser depth routing technology
Depth routing manufacture is hard to control for lamination press thickness tolerance,glue overflow,accurate of mechanical routing problems. But use laser milling, it’s excellent of accurate and no other difficults.
Bubble and overflow glue are common questions of FPC quality.Coverlay flow follow press temperature go up lead to copper pad adhesion glue like epoxy.
The reasons of glue overflow
It involve many aspects,like coverylay protection in process,FPC factory technology parameter,environment protection,worker operation,etc.
One of reasons: Coverlay parameter when making.
When CL is coating and baking,if the temperature,time and parameter controlled improper,it will cause glue overflow in prepreg.
The second reason: Coverylay storage environment
The correct storage environment temperature is under 10℃,optimum storage environment temperature is 0℃－5℃,validity period is 90 days.if the storage temperature is incorrect, coverlay is easily absorb moisture and go into stability lead to glue overflow.
The third reason: If CL match FCCL
In the design of layer stackup, FCCL and CL need coherence. If the thickness of Coverlay and Copper have big different, it’s easier lead to glue overflow.
The fourth reason: The design of FPC
Follow the high density interconnector products approach,appeared isolate pad design lead to glue overflow.
The fifth reason: FPC technology parameter
In set up of FPC technology,like pressure is overstrong,time is overmore, press machine’s press is inequality,all these factors can lead to glue overflow.
The solution of solve glue overflow:
We have know the reasons lead to glue overflow,so we can make different solution for different problem.
Coverlay making problem:
FPC factory should strict inspection the incoming material,if any unqualified material should return to supplier avoid effect FPC fabrication.
Storage environment
As validity period of CL is less than two months,so FPC factory should have freezer to store the CL materials.If CL got moist as save improper,they can through low temperature baking the CL before use and temperature should be 60－80℃；2~4 hours, it will great improve the glue overflow problem.
Isolate pad
This kind of phenomenon is the most common quality problem of all FPC factories. If we change technology parameter as glue overflow problem,it will bring bubble or peel strengthen problems.if miscontrol of glue overflow,need use 2% NaOH to immerse and through brush machine can clean glue smear.
In press process, operator need strict follow instruction to make register, and strengthen inspection control avoid register inaccurate lead to glue overflow.
At the same time, factory need strict follow 5s to inspection if CL be contaminated,if have burr, develop workers with good operating habit,improve productivity.
If the vias is too close to pad, solder will flow out through via when make reflow soldering,lead to false weld.
Countermeasure: Move vias to 0.2mm far away from pad.
This kind of question always happened to PCB design. Engineer had to save space for boards limited by dimension. But it may lead to serious problem for SMT.
Any other PCB technology knowledge: www.kingsunpcb.com
Flex-Rigid PCB is mix FPC and Rigid PCB,followed special requirement and press them together. It’s compatible both of FPC and Rigid PCB advantages.Enginner always use 2 rigid PCBs,a flex pcb and a switch to connect them before Flex-Rigid PCB be published.Flex-Rigid PCB have strong resistance for bad application environment,it’s good apply in medical equipment and military facility. In order to improved the connect reliability between flex PCB and rigid PCB,PCB manufacture developed Flex-Rigid PCB.
Smart phone is still the biggest market of Flex-Rigid PCBs.more and more function required ,like legend edit,email handle,picture element enhance of digit camera,etc.follow mobile TV,Mini projector,Map function strengthen and other mobile function diversification, Flex-Rigid PCB will application in module and whole equipment.
Flex-Rigid PCB advantages:
1.Lighter 2.Dielectric is thin 3.Transmission routing is short 4.Small through hole 5.Small noise signal,high reliability 6.Flexible to change shape in special space requirement. 7.Resist high and low temperature and fire. 8.Can fold and don’t effect the transmission. 9.Against electrostatic disturbance.
Flex-Rigid PCB weakness:
1.The fabricate technology is complex : involved rigid PCB and Flex PCB technology, it’s very complex make them at the same time. 2.The cost of equipments are expensive for both rigid PCB and flex PCB. 3. Use: if one board damages, another boar is unuseful.
The process of Flex-Rigid PCB.
The technology difficult of Flex-Rigid PCB:
Below is a 6 Layer Flex-Rigid PCB with symmetry stackup and one flex PCB.
1.All Flex board plating process used tow board avoid Flex board too thin to scrap. 2.Press PI cover with carefully and no air bubble. 3.Rigid PCB use depth milling to making for flex PCB, and PP used no-flow type avoid overflow when press lamination. 4.The inflate and shrink ratio is different between flex PCB and rigid PCB.
Here two PCBs file need to combine one PCB file, it will save much setup fee for prototype.How to build one PCB file with different PCBs in Allegro?
Below is the second PCB.
We create a new PCB module.and select follow the red circle.
Save the module with mdd.then copy the second PCB into the first PCB.
The first PCB select like below:
Then you can see we combined the second pcb into the first PCB through place component method, you need named it when place the new module.after that every legend stick up the name,so we can use below method to solve this problem.
In the second PCB,save the silkscreen layer with correct format.
Input the correct silkscreen layer into the first PCB.
Then the silkscreen is perfect now.
This artcle from PCB_technique. more questions please contact us: www.kingsunpcb.com
It’s important to know factors affecting of PTH throwing power to electronics products, then improve high aspect ratio for facilitating productivity.it’s good for electronics products reliability,reduce fabrication cost,improve productivity.
PTH
Plated through hole(PTH) is the crucial process of PCB manufacture. it need be plated enough copper in wall of hole for connect different layers. The copper thickness is very critical for good PCB.
Throwing Power(TP)
Even-plated of through hole is a important factor to adjudge PTH. we call it throwing power,It’s the ratio of plated copper thickness between center point to edge of hole.
Aspect ratio
Throwing power is always relative aspect ratio. When aspect ratio is low,it means board thickness is thin and hole is big.it have enough space for ion spreading,power is adequate distribution when plating.so the TP is high. If aspect ratio is high,it occur “dog bone” result, the TP capability is low.
The plated of hole wall distributed evenly ensure PCB have good reliability and stability in surface Mount Technology and usage, it great increase longevity of products.
Improve productivity:
Plating process is bottleneck of PCB manufacture.High TP capability can shorten the process time and increase capacity.
Reduce manufacture cost:
TP improved 10% can reduce 10% material consumption and promote international competitive power.
