Important PCB Checklist

Gone were the days where you need to wait for a few days before receiving a PCB quote from PCB suppliers and another couple of days to confirm a purchase order with them. With the fast development of internet technology, most PCB suppliers make full use of it and make online purchase much convenient  for customers. Currently, online PCB purchase can be done just within a few clicks. 

1.PCB CostMake sure the online ordering page offers you a complete quote, including an estimated shipping costs. Because you do not want to be surprised by any hidden costs when finally pay for your PCB online.

2.PCB Lead TimeDo not rush to click the purchase button. Make sure the PCB lead time matches your expectation. If you choose a shorter lead time while you don’t need, the cost may be higher.

3.Manufacturing FilesMost suppliers accept Gerber files, while some can manufacture your PCB from the design file itself. Depending on your preference, you should upload files accordingly before ordering the PCB online.

4.Layer Number

You need to make sure that the PCB layer you choose on the website fits your design. Most suppliers make double layers as default. If you need a multilayer PCB, different suppliers offers a different range of options for you.

5.PCB MaterialsMost suppliers have FR-4 as default because it is the most common PCB material. If your design requires other materials, be sure to contact the supplier before placing an order, or you can find alternative materials on the page to choose from.

6.PCB SizeSince various suppliers have different PCB manufacturing capability, if you are designing a fairly large PCB, you’d better contact with customer support team online. 

7.PCB Solder MaskThe default and cheapest solder mask color is green. Suppliers also can offer other color options, but these may be more expensive.

PCB Fabrication Materials

Although there is a wide variety available, all PCB fabrication materials are supposed to meet some standard criteria. The properties needed include high dielectric properties, low flammability in laminated plates, high conductivity for materials used on connecting components together etc. We will describe the most used PCB fabrication materials individually in the paragraphs below.

Copper-- is the metal used for conducting lines serving power and signal connections. Copper has a very high electrical conductivity and is relatively cheap.

Fiberglass-- is a fiber reinforced plastic used as an insulating material. It also had rigid property and is quite resistant to mechanical forces. There are standard thickness of fiberglass boards and standard types. Most types used are FR-2 and FR-4 which have better performance, but FR-2 is more expensive than FR-4. 

Gold-- is sometimes used to connect chip pins because of its good corrosion resistance performance.

Lacquer-like polymer-- is a polymer type used for soldering masks. The solder mask is a layer stretched across the entire PCB to prevent corrosion, external electric charge and dust. Different materials are added to the solder mask to get different colors, but mostly they are green.

Polyester-- is a naturally existed polymer in some plants. It is biodegradable and therefore eco-friendly. Polyester is used for printing silkscreen on the PCB board surface.

Polyimide-- is a polymer type used in flexible PCB boards. Polyimide is characterized with highly flexible, high dielectric properties, thermo-resistance, and is well-known for its unique orange color.

Solder alloy-- is a metal mixture of copper, tin, cadmium, silver, and other materials used to solder components on the board. It has a lower melting temperature than other materials it has contact with during soldering process. It has good electrical conductivity properties, close to those of copper and silver.

Except those materials mentioned above, there are dozens of other PCB manufacturing materials. The type of materials used depends on the quality you require, total product fabrication budget, and the environment in which the PCB will operate.

Considerations for High Frequency PCB Design

High-frequency PCB design requires a completely different set of knowledge compared to simple low-speed analog design or digital circuits design. Ignoring some of these practices may make the design be highly susceptible to EMI or cause signal loss. We here list some considerations for you when design a high frequency PCB.

1.Impedance MatchingImpedance matching is a key factor in high-frequency PCB design. As the frequency increases, the tolerance becomes lesser. Therefore, the designer needs to ensure that the impedance matches at the specified value.

2.Material SelectionUnlike low-speed or frequency designs, material selection is critical for a high-frequency PCB design. FR-4 here is not the best choice, because it can not achieve consistent dielectric constant of the PCB which is required by high-frequency design. This can lead to unacceptable signal losses in a high speed design.Instead, the ideal material for high-speed designs should have a much lower loss dissipation factor than the FR-4. In high-frequency design, even the slightest moisture of the PCB can affect the circuit itself. It is important to use a low moisture absorption material like PTFE.

3.Minimal SoldermaskYou may have chosen a suitable substrate for high-frequency design. But if you do not pay attention to the thickness of the solder mask, your design will still suffer from signal loss. Solder mask has a high moisture absorption rate, and wet solder mask is not suitable for high-frequency transmission.

4.Return LossReturn loss for a high-frequency design must be kept to the minimum. Since high-frequency signals use the least-inductive path, there should be no discontinuity in the ground plane below the signal traces themselves. Otherwise, high-frequency signals will use other non-ideal return paths, such as the power supply plane, and may cause ringing or reflections.

PCB Design Tips to Reduce Electromagnetic Interference Part2

PCB design becomes more difficult since electronic equipment have been more sensible and required excellent capability to reduce noise and electromagnetic interference. Thus, how to improve the design becomes one of the key issues that many engineers are concerned about. This article describes some tips for reducing noise and electromagnetic interference when designing PCB boards.

11.Single-sided board and double-sided board access to power and grounding by single point, thus power lines and ground lines should be as thick as possible.

12.Keep clock, bus wire and chip select signals far away from I/O lines and connectors.

13.Keep analog voltage input line and VREF away from the digital signal lines, especially the clock.

14.For A/D components, the digital part and the analog part should be unified rather than cross.

15.Both component’s pins and decoupling capacitor’s pins are as short as possible.

16.The key lines should be as thick as possible with protection on both sides, while high-speed lines should be short and straight.

17.Don't keep noise-sensitive lines parallel with high-current, high-speed switch lines.

18.Do not route below quartz crystals and noise sensitive components.

19.No current loop around weak signal circuit or low frequency circuit.

20.Do not form a signal loop, if inevitable, keep the loop area as small as possible.

21.One decoupling capacitor per integrated circuit. Add a small high-frequency bypass capacitor to the edge of each electrolytic capacitor.

22.Use high-capacity tantalum capacitors or poly condenser capacitors instead of electrolytic capacitors for charging and discharging storage capacitor. When using tubular capacitors, the housing should be grounded.

PCB Soldering Issues

PCB pads are easily peel off when the circuit board is being soldered or under repaired. In this article, some reasons for the falling off pads are analyzed, hope it is useful for your next project.

Reasons for easily falling off pads

1.Board quality issue. Due to the poor adhesion of the resin adhesive between the copper foil of the copper clad laminate and the epoxy resin, even the copper foil with a large area copper is slightly heated or mechanically stressed, it is very easy to separate with the epoxy resin which leads to the pad off, copper foil off and other issues.

2.Circuit boards' storage conditions.Affected by the weather or stored in the humid place for a long time, circuit boards absorb too much moisture. To achieve the desired soldering effect, SMD soldering needs to extend soldering time and temperature to compensate for the heat away due to moisture evaporation. Such soldering conditions easily separate copper foil and epoxy resin.

3.Problems caused by soldering irons.Generally, the adhesion capability of PCB boards can endure ordinary soldering process, which means no pad off phenomenon will happen However, electronic products generally needs repaired when running for a long time, repair by soldering iron is always the top choice. While the local high temperature of electric soldering iron can reach 300-400 degrees, and this made the temperature of pads up too high immediately, then resin will be off due to high temperature soldering, and pads will definitely be peel off.

Since pads are easily fall off, PCB manufacturers should take following steps to improve solder resistance to meet customers’ needs.

1.CCL suppliers should have good reputation for high-quality substrate they produced. Generally, copper clad fiberglass material selection and lamination process should ensure that the circuit board made of solder resistance will be in line with customer requirements.

2.Put desiccant and vacuum packaging the PCB board before shipping. Keep the circuit board always dry can reduce virtual welding and improve solderability. 

3.As to the effect about thermal shock caused by the soldering iron on pad, try to increase the thickness of the pad by plating copper foil. In this way, when the soldering iron heats the pad, the thermal conductivity of the copper pad is greatly enhanced, effectively reducing the local high temperature of the pad, and at the same time, the thermal conduction makes the pad detachable more easily and the soldering resistance of the pad is achieved.

Not to Touch PCB Boards by Hands

It is the common sense for PCB engineers that man can not touch the circuit boards directly by bare hands, but why? In this article, let’s find the reasons together.

1.The dangers of static electricity

Under different circumstances, electrostatic voltage carried by human body vary from several volts to hundreds volts to tens of thousands of volts. Touch electronic components directly by bare hands will generate electrostatic discharge, then devices are easily damaged and reliability are reduced; even worse, electrostatic discharge can make causes the device breakdown at once.

In addition, the electrostatic discharge process simultaneously radiates radio waves at a certain frequency and interferes with peripheral microprocessors, causing the application to run in disorder and seriously affecting the normal operation of the device.

Therefore, try to avoid direct human contact with electronic components in the daily work, especially in the charged state.

2.Effect by static electricity on the core board feedback loop

Human touch (the introduction of human equivalent resistance and other interference) can change the characteristic of feedback loop (including the pole offset), resulting in feedback loop oscillation and instable DC-DC output voltage.

Instable DC-DC output voltage can make the system restart (DC-DC automatically reduce the output voltage), even worse, it will burn out the main circuit board (DC-DC automatically adjusts the output voltage), thus the charged motherboard is not allowed to touch.

3.How to prevent the static electricity

a.anti-static cordless wrist band

According to the corona discharge effect and the principle of the tip discharge, when the accumulated charge exceeds a certain value, the potential difference is discharged to the space to achieve the purpose of eliminating static electricity. Static dissipative time: less than 0.5s; features: convenient, reliable.

b.anti-static wrist strap

Human skin contacts with the wrist strap made from the static conductive material directly, thus when the wrist strap grounding, discharge static electricity generated by human can be quickly discharged. Electrostatic discharge time is less than 0.1s.

c.anti-static PU coating gloves

Anti-static PU coating gloves can further prevent static electricity from being transmitted to printed circuit boards by hand contact. Hand back conductive wire spacing is 10mm.

4.Hardware protection

Electrostatic discharge immunity: air discharge ± 15KV, contact discharge ± 8KV;

Electrical fast transient burst: interference frequency is 5KHz or 100KHz, pulse group time 300 (1 ± 20%) ms;

Lightning (surge) immunity: 2KV capacitive coupling and gas discharge tube coupling, 1 time/min;

Conducted harassment immunity: 3V capacitive coupling and gas discharge tube coupling, test frequency is from 150KHz to 80MHz.

5.Software protection

The operating system is usually stored in Flash. Static interference of the Flash and unexpected power-off are prone to make the operating system lost and the file system damaged. Except the normal operation system, design a backup system in the normal flash storage area is necessary, thus when something wrong goes about the Flash, the backup system starts automatically to ensure that the product is still able to work stable.

Now you must understand why it is not allowed to touch the printed circuit board by hand, right?

2018 PCB Industry Forecast

PCB industry really did a good job in 2017, amazing data means a prosperous market in 2018. ITRI held a forecast for Taiwan's manufacturing industry, and once again revised up its output growth rate of manufacturing industry to 4.04% this year. It is expected that under the steady growth of the global economy, the growth of manufacturing industry next year will have an estimated annual increase of 3.25% and the output value can reach RMB18.15 trillion.

IEK predicted that next year the global economy was expected to continue this year’s growth trend. With the steady external demand and the gradual improvement of major electronic products like TV and smart phones, it was expected that China would have a sound manufacturing and sales performance. Manufacturing orders for semiconductors and machinery would be expected to inject momentum into manufacturing and sales growth momentum.

Although the global economy will grow steadily next year, the policy uncertainty of the major economies will increase the risk. The United States Federal Reserve will start to reduce its balance sheet plan, and monetary policy will enter into a double-stage tightening phase of raising interest rates and narrowing down the stocks. 

IEK suggested that the government should expedite the negotiation of the Taiwan-US economic cooperation agreement to help the industry deepen the connection with US end-customers and the supply chain. According to the statistics of the World Industry Association Database of the EU, the manufacturing industry in Taiwan and the United States has been developed fast in recent years and the U.S. industry demand has simultaneously led to the improvement of manufacturing industry in Taiwan province. 

Shih Hsin University professor Zhou Ji was invited to attend the meeting. He pointed out that according to the IEK data, the manufacturing rate maintained a high level. Among them, the peak of information electronic production capacity was up to 132%.