info@kingsunpcb.com, Author at King Sun PCB

Flex Circuit Board Rework And Repair

Flexible circuits are used in various applications where conductors are connected to each other,these conductor interconnections must be bendable or be able to remain bent for long periods of use. In the past, this interconnect technology was implemented using wire interconnections.

There are many kinds of flexible circuits:

One is a two-way access flexible circuit, which is a single-sided flexible circuit, the purpose of making this circuit is to connect conductive materials from both sides of the flexible circuit.

The second is a double-sided flexible circuit, which a circuit with two conductive layers, two conductive layers are located on both sides of the base layer in the circuit. For your specific requirements, you can form trace patterns on both sides of the substrate sheet, traces on both sides can be interconnected by copper plated through holes.

The third type is a multilayer flexible circuit, which combine several single-sided or double-sided circuits with complex interconnections, shielding and surface mount technology are often used in multi-layer designs.

The fourth is the rigid-flexible circuit, combines the advantages of both rigid printed circuit boards and flexible circuits, the circuit is usually interconnected by plated through holes between rigid and flexible circuits.

Flexible circuit has many advantages. One of the main benefits of flexible components is the ability to implement virtually error-free cabling, replacing labor-intensive manual cabling, In addition, unlike rigid circuits, flexible circuits can also be designed into complex three-dimensional structures,because you can bend them into various shapes. As the name implies, materials used in flexible circuits can bend back and forth numerous times, this means that they can be used for highly repetitive applications, for example on a print head. Flex circuits are very good substitutes for rigid circuit boards and wires when it comes to considering the weight of the product,as its dielectric materials and conductor lines are very thin.

In the past few years, the demand for the flexible circuit industry has been growing, now the annual output value of the flexible circuit industry reaches 10 billion U.S. dollars, and the annual growth rate reaches 7% – 10%.

With the rapid growth in the use of flexible circuits, the rework standards for these types of electronic interconnect circuits (replacement devices still meet the original specifications and functions) and repair standards (to repair physical damage on flexible circuits) have not kept synchronization.

There are some rework challenges from the characteristics of the flexible circuit itself. First, it is difficult to keep the flexible circuit flat during rework, From the perspective of rework, the bendability of Dupont materials or other basic flexible materials is a challenge to rework. Although their flexibility is their advantage in application. In order to keep the assembly flat, it must be taped to keep it flat. In some cases, making a vacuum fixture for the rework of a flexible circuit is a more expensive approach. The vacuum structure of the fixture has a great influence on the rework union when placing the fine-pitch elements. If the vacuum is just below the lead of a micro-pitch device, a slight vacuum may “pull” the flexible wire into the hole so that the device cannot contact the wire of the flexible circuit, resulting in an electrical “open circuit”. For solder paste printing on rework, coplanarity is a challenge when the stencil and the surface to be printed are not coplanar. Therefore, it is often necessary to use a syringe to apply solder paste instead of print coating. Sometimes, flexible materials with conductive epoxy are used in the interconnect device. Although the curing temperature of these materials is much lower than the standard solder reflow temperature, it may mess things up. In this case, as long as the design of the rework process is correct, the limitation on multiple rework is that the marginal cost of the component is much lower than the cost caused by rework. At this time, reworking a large amount of waste products is a more attractive economic option.

From the process point of view, the process of reworking flexible circuits has some advantages. The thermal mass of the flexible circuit board is smaller than that of the rigid printed circuit board. When soldering a flexible circuit board, the heating time to the liquidus temperature is shorter than the rigid circuit board.This speeds up the replacement process of the rework process. In addition, this reduces the temperature of the air from the hot air system required for welding by several times, and the possibility of hot air causing component damage is relatively small. The high temperature resistance of flexible materials, high temperature resistant polyimides, makes the process window for the flex circuit rework process large.

According to industry standards for repairing PCBs, IPC 7711/21 repairs and modifies printed circuit boards and electronic components to cover the rework and repair processes of various flexible circuits, Each of the processes listed in this standard, based on the suitability of each process for rework or repair of flexible circuits, is preceded by the letter “F” under the heading “Board Type” in the upper right corner of the process documentation. There is even a flexible circuit-specific conductor repair standard in this standard. Various processes covering repair conductors on flexible circuits in step 7.1.1.

The rework and maintenance technology of flexible circuit components is continuously developing, and the rework and repair of flexible circuit components still face enormous challenges. Since the electronics assembly industry has long been a rigid circuit board, it is a good idea to use the rigid circuit board as the basis to find the best rework method for flexible circuits.

Posted on 24 Apr 2018
By info@kingsunpcb.com
In FPC Technology, PCB knowledge

Why PCB Solder Mask Peeling Off When Welding?

Why the insulation solder mask on the board will peel off after the PCB passes the automatic soldering furnace.

There are three major possibilities for solder mask peeling off:

The first possibility is that the nature of solder mask oil is insufficient to withstand the test of solder furnace. This may be due to the failure of the solder mask oil due to expiration or poor operation.Green Solder mask oil used by the industry are almost always subjected to test procedures such as heat resistance and reliability.Therefore, there should be no problem with normality. In this regard, it is necessary to review whether the material itself has changed or the process has changed.

The second possibility is the influence of external forces,include flux supply and mechanical collisions,Especially under high temperature conditions, solder mask oil properties no longer have a high hardness like normal temperature environment.At this point, the solder mask surface of the circuit board is easily scratched and peeled off by any external force.

The third major possibility is PCB circuit board bursts due to moisture absorption before or when solder mask is applied,Water vapor expands nearly three hundred times in volume when heated and gasified.Instant warming plus green paint softening,It’s very easy to make solder mask peel off.This kind of problem will occur in the process of hot air solder leveling produced by the circuit board, and it may also occur in the assembly processes such as wave soldering, reflow soldering, and so on.

There are several possibilities for SMPEELING after ENIG

The treatment in front of the copper is not perfect.
Insufficient drying before S/M coating.
The stagnation time is too long to generate an oxide layer.
The material of the solder mask itself is not suitable for the gold process.
The fifth may be insufficient solder mask polymerization
More than one high temperature process.For example, gold and gold plating together or gold leaching twice may also occur

There are many possibilities, you have to do a detailed analysis to clarify each item, but in general it is important to use S/M types.Some special solder mask, slow response to UV light,it requires anaerobic and relatively high exposure energy to reach a high degree of polymerization.If the exposure polymerization is insufficient, there will be no way to fully achieve the required polymerization intensity in subsequent baking.If you use such materials, you should clearly inform the operator of the correct method, otherwise the problem will continue.

Posted on 19 Apr 2018
By info@kingsunpcb.com
In PCB Soldering

What Is PCB Laser Drilling And Application

With the continuous development of science and technology, PCB laser drilling is more and more widely used.Here, let the flexible circuit board manufacturers introduce the following 2 intuitive phenomena: what is PCB laser drilling and the matters needing attention.

How does laser produce?

Laser is a gas mixture gas in a closed circular space (see below table) under the strong fan’s wind.When the gas mixture passes through a charged ceramic electrode,the mixture gas make chemical reaction of molecular structure and reflect from the whole reflector,then form the laser beam and emit from the seismograph.

Why laser drillingburn thousands of holes in a second?

After the laser beam is generated, a series of refraction of light—> reflection—>splitting—> light correction and so on are needed.Finally, arrive at the electronic scanning mirror, and control the frequency of the X axis and the Y axis motor through the program with 2250 changes per second.Each time the frequency is changed, the position of the hole is changed, so that the holes with different coordinates can be reached. See below picture, a scanning mirror2. Why laser drillingburn thousands of holes in a second

Why gas mixtures are often replaced

When gas mixture gas passes through charged ceramic electrodes, the chemical reaction of molecular structure occurs.The composition of gas mixture which has been formed in a certain proportion has changed.Therefore,the mixed gas that has changed the structure will affect the generation of laser after long time used, lead to instability of laser will also affect the quality of hole burning.Therefore, we need to replace the gas quickly after 96 hours and replace it automatically after 720 hours.

How much small holes can be made by laser drilling?

According to the size range of the small hole, it is divided into six gears:

Small holes: 1 to 3 (mm);

Small holes: 0.40 to 1 (mm);

Ultra small holes: 0.1 to 0.40 (mm);

Micropores: 0.01 to 0.10 (mm);

Secondary micropores: 0.001 to 0.01 (mm);

Ultra micropores: <0.001 (mm).

Laser drilling applicable materials and industry applications:

The laser drilling is mainly non-contact metal drilling.
Ultramicropore punch
The minimum via size can reach 0.01mm. It is suitable for punching of ordinary metals and alloys (all metals such as iron, copper, aluminum, magnesium, zinc, etc.), rare metals and alloys (gold, silver and titanium).

Posted on 12 Apr 2018
By info@kingsunpcb.com
In FPC Technology

10 Mistakes New Designer Always Make In PCB Design

PCB design mistake 1: Overlap of weld pad

The overlap of the pad (except for surface welding) means the overlap of holes. In drilling process, drill holes will be broken due to multiple drill holes, resulting in damage to holes.
The two holes in the multi-layer plate overlap, such as one hole position for the isolatingpad, and the other for connection pad (thermal welding pad), so that the film is shown as isolate pad,lead to PCB damage.

PCB design mistake 2:The abuse of the graphic layer

Some useless connections were made on some graphic layers, which were originally designed as four layers, but five layers of lines were designed, resulting misunderstanding in PCB design.
It saves time in PCB designing the time graph. Taking Protel software as an example, we use Board line to draw lines, and use Board layer to draw marking lines.In this way, when we make film, we fail to select the Board layer and miss the connection.Or it will be short circuited due to the selection of Board layer’s annotation line, so the graphic layer should be kept intact and clear when PCB designing.
Violation of conventional design, such as componentside at Bottom layer, welding side at Top layer, causing inconvenience.

PCB design mistake 3:The character setting

The character covered SMD welding pad bring inconvenience to PCB’s E-test and component welding.
The design of characters is too small, resulting in difficulties in screen printing. Too big characters overlap and difficult to distinguish.

PCB design mistake 4: The setting of the aperture of a single side pad

The single side pad usually does not drill. If the hole needs to be marked, its apertures should be designed to be zero.If the value is designed, the hole coordinates will appear when drilling data is generated, and there will be a problem.
Single side pad need drilling, should be specially marked

PCB design mistake 5:Draw pad with a filling block

Usingfilling blocks to draw pads can be checked through DRC when designing lines,but it is not suitable for processing. Therefore, solder pad cannot directly generate solder resist data.When the solder mask printing, the area of the filling block will be covered by solder resist, resulting in the difficulty of device welding.

PCB design mistake 6:The ground and power layer are both thermal pad and the connection line

Because of the design of a power layer is negative layer,it is the opposite of the actual printed board,and all the wires are isolated lines, and the designer should be very clear.It should be careful when drawing several sets of power supply or isolation line of several kinds of land. It should not leave a gap, short the two sets of power, and do not block the area of the connection (a group of power is separated).

PCB design mistake 7:Definition of processing layer is not clear

The single layer PCB design is on the TOP layer. If it is not stated, it is possible that the boards made are not equipped with devices.
For example, a four layer board is designed with TOPmid1 and mid2 bottom four layers, but it is not placed in such order, which requires instructions.

PCB design mistake 8:There are too many filling blocks in PCB design, or filling blocks are filled with very thin lines.

The films will miss data, and the data is incomplete.
Because the filing block is drew on line by line in the process of plotting data processing, the amount of data produced will be quite large, which increases the difficulty of data processing.

PCB design mistake 9:Surface mounting pad is too short

This is for E-test, for too dense surface mount components, the distance between the feet is very small, and the pad is also quite thin,to install test pins, the upper and lower (left or right) positions must cross placed.If the pad design is too short, though it will not affect the components installation, it will make the test needle wrong.

PCB design mistake 10:The space between large area grids is too small

The edge between the large grid lines is too small (less than 0.3mm).In PCB manufacturing process, drawing process is prone to produce a lot of broken films on the board after finishing film development, causing breakage.

Posted on 10 Apr 2018
By info@kingsunpcb.com
In PCB design

PCB Surface Immersion Silver Problem And Solution

The present situation

Printed circuit boards cannot be reassembled after assembly, the cost loss is very high caused by microvoid.The problem is due to PCB design defect lead to weldability,it has been verified by the original equipment manufacturer (OEM).It has nothing to do with immersion silver or other final surface treatments.

Root cause analysis

By analyzing the root cause of defects, we can minimize these defects through process improvement and parameter optimization.Galvanic attack usually occurs on the cracks between the solder mask and the copper surface.In the process of immersion silver, because the cracks are very small, the silver ion supply to immersion silver is limited,but the copper here can be corroded into copper ions,then occured immersion silver reaction on the copper surface outside the crack.Because the ion conversion is the source of the silver reaction,therefore,the extent of attack under the crack is directly related to the thickness of immersion silver.2Ag+ + 1Cu = 2 Ag + 1Cu++(+ is a metal ion that loses an electron).There is a crack in any of the following reasons:The side corrosion / development is too excessive or the solder mask is not well integrated with the copper surface.Uneven copper plating (hole and thin copper); obvious scratch on copper substrate under the solder mask.

There are several ways for silver to be contaminated by sulfur,The reaction of silver and oxygen is another process, which is usually produced by reaction of oxygen and copper under the silver layer to form dark brown copper oxide.This defect is usually due to the rapid immersion silver and form low density immersion silver layer, lead copper in the lower part of the silver layer is easy to contact with the air,so copper reacts with oxygen in the air,Loose crystal structure has larger intergranular voids, which requires thicker silver deposits to achieve oxidation resistance.This means that the thicker immersion silver layer should be in production, which will increase the production cost,it also increases the probability of the problem of solderability,such as microvoid and bad welding.

Solution to avoid immersion defect

In addition to excellent performance, a perfect immersion silver technology must also meet the requirements of safety, environmental protection and reliability.The immersion silver process has 7 steps, of which three are water washing steps. Its performance and advantages are as follows:

Pretreatment is divided into four steps: oil removal, water washing, micro corrosion and water washing.The surface tension of the degreasing solution is very low, which can moisten all the copper surfaces.It not only eliminates the problem of copper exposure, but also promotes the deposition of silver layer in high aspect ratio pores and micro through-hole.The unique micro etching formula can produce slightly roughened and half bright surface structure.Such a surface structure is conducive to the formation of a fine and dense crystal structure of silver, so high density and low porosity immersion silver can be obtained even when the thickness of the silver layer is very low.This greatly improves the corrosion resistance of the silver layer.

Immersion silver is divided into three steps: prepreg, immerse silver and final deionized water washing.There are three purposes for the establishment of prepreg. The first is the use of sacrificial solution to prevent contamination of silver concentrate from copper and other substances by micro etching tank.The second is to provide clean copper surface for silver replacement reaction, so as to get the same chemical environment and pH value of copper surface.Since the composition of the prepreg is the same as the silver depositing liquid (except for the metal silver), the third function of this process is the automatic replenishment of the silver sink.In the immersion silver reaction, the consumption of metal silver is the only consumption, and the change of the organic content in the silver concentrate is only caused by the loss of the liquid.However, the amount of the prepreg and the silver immersion solution is the same. The amount of the pre impregnated belt is equal to the amount of silver carried out, so immersion silver does not accumulate unnecessary organic matters.The immersion silver reaction is carried out through the displacement reaction between copper and silver ions.The copper surface treated by micro etching technology can ensure that the uniform immersion silver can be generated slowly under the controlled rate of silver deposition.Slow immersion silver speed is conducive to depositing dense crystal structure, avoiding particle growth due to precipitation and caking, and forming high density silver layer.The immersion silver layer with tight structure and moderate thickness (6 – 12U) has not only high corrosion resistance but also very good electrical conductivity.The immersion silver liquid is very stable, has a long life cycle and is insensitive to light and trace halides.It greatly reduces the downtime, low ion pollution and low equipment cost.

Conclusion

This immersion silver process concentrates on the best properties of several final surface treatments.It meets and surpasses the requirements of the global PCB industry for solderability, reliability, safety and compliance with regulations.Wide operation windows, easy operation, control and maintenance, can be reworked, and the lowest cost is produced in the same final surface treatment.In view of the above six problems related to silver immersion technology, the direct impact of these problems on high quality products is eliminated or reduced. In addition, the technology is in accordance with the regulations of RoHS and WEEE, and the silver deposit is completely lead-free.

Posted on 4 Apr 2018
By info@kingsunpcb.com
In PCB knowledge

Rigid-Flex Circuit Boards Pros And Cons

The early process of Rigid-flex PCB board is use connector or hotbar process to connect two PCBs with flex board.This combination with the flex board and rigid PCB process is time-consuming and laborious, so customers transfer the assembly to PCB manufacturer to make rigid-flex PCB.

In addition to the price, the use of Rigid-flex Board has many advantages, listed as follows:

It can effectively save the space on the circuit board and save the use of the connector or the HotBar process

Because of flex PCB and rigid PCB get together, so that require the use of connectors or HotBar process space can be saved, saved space is very important for some high density board,it also saved the cost of using the parts of the connector or the cost

of the HotBar process.

In addition, the space between the two pieces of the board can also become more compact because it saves the connector.

The distance of the signal transmission is shortened and the speed is increased, and the reliability can be improved effectively.

The traditional transmission of the signal through the connector is circuit board —>connector—>flex board—>connector—>circuit board. The signal transmission of rigid-flex PCB is reduced to the circuit board—>flex PCB—> circuit board.The distance between signal transmission is shorter, and the problem of signal transmission attenuation between different media is also reduced.The wiring on the general circuit board is copper material, and the contact terminal of the connector is gold-plated. The solder joints are plated with tin, and solder paste is applied to the printed circuit board. The transmission of signals between different metal will be attenuated.If we change to rigid-flex boards, these media will become less, and the ability of signal transmission can also be improved.

Simplifying the assembly of products and saving the time of assembly

The use of rigid-flex PCB can reduce the time of SMT process, because the number of connectors is less.It also reduces the time for the assembly of the whole machine, because it saves the assembly of the flex board into the connector, or saves the process of the HotBar. It also reduces the cost of part management and inventory, because the BOM table is reduced, so management becomes less.

The disadvantage of rigid-flex PCB:

After comparison,the biggest weakness is that rigid-flex PCB boards is more expensive.The cost is nearly doubled than flex PCB +rigid PCB.But if the price of the connector is deducted or the cost of HotBar, the price is likely to be same. Another disadvantage is that both SMT and carrier may need to use a tray (carrier) to support the part of the flex board, which virtually increases the assembly cost of the SMT.

Posted on 3 Apr 2018
By info@kingsunpcb.com
In PCB knowledge

How To Calculate PCB Trace Width/space And Current In PCB Design

When we design PCB, it’s necessary consider how to calculate PCB trace width/space for the through current.so what is the relationship between PCB trace width and space and current? The following is a brief explanation of this:

The PCB trace width/space and current calculation method is as follows:

Calculate PCB trace area

The thickness of the copper foil for most of the PCBcircuit board is 35um. It is multiplied by line width is the section area, and is converted into square millimeter.There is a current density experience value for 15~25 ampere / square millimeter,The flow capacity is obtained by multiplying it by the sectional area.

T is the maximum temperature rise, the unit is centigrade (the melting point of copper is 1060 degrees C).

A is a copper cladding area with a unit of square MIL (not millimeter mm, square mil.).

I is the permissible maximum current, the unit is ampere (AMP)

General 10mil=0.010inch=0.254 can be 1A, 250MIL=6.35mm, 8.3A

Data of calculate PCB trace width/space and current

The calculation of PCB current carrying capacity has always been lacking in authoritative technical methods and formulas. Experienced CAD engineers can make more accurate judgments depending on their personal experience.But for a new CAD designer, it is difficult problem.

The current carrying capacity of PCB depends on the following factors: PCB trace width, PCB trace thickness (thickness of copper foil), allowable temperature rise.

As you all know, the PCB trace is wider,the capacity of the carrier is greater.Here, please tell me: assuming that under the same condition, the 10MIL line can withstand 1A, then how much current can be borne by the 50MIL’s walking line, is it 5A? the answer sure is no. Please see the following data from the international authority:

The unit of line width is: Inch (inch =25.4millimetres, 1oz. copper =35 micron thick, 2oz.=70 micron thick, 1OZ=0.035mm.)

Experiment of calculate PCB trace width/space and current

In the experiment, we also have to consider the pressure drop caused by the line resistance produced of length of the wire.The tin in the process welding is only to increase the capacity of the current, but it is difficult to control the volume of the tin. 1OZ copper, 1mm wide, general 1-3A galvanometer, you look at the specific length, the pressure drop of the requirements.

The maximum current value should refer to the maximum allowable value under the limit of temperature rise, and the fusing value is the value of the temperature rising to the melting point of the copper. Eg. 50mil 1oz temperature rise 1060 degrees (that is, copper melting point), the current is 22.8A.

Posted on 29 Mar 2018
By info@kingsunpcb.com
In PCB design

Ceramic Circuit Board VS Metal Core PCB

Ceramic circuit board and Metal PCB are good in heat dissipation of PCB board.The application of the traditional LED heat dissipation substrate,Metal Core PCB (MCPCB) is different from the application range of ceramic heat dissipation substrate.MCPCB is mainly used in the system circuit board.The ceramic circuit board is applied to the LED chip substrate.However, with the evolution of LED requirements, the two are gradually applied to the process of COB (Chip on board).The following we will discuss and compare the two material.

The ceramic circuit board is a kind of heat conducting ceramic powder and organic binder, and the heat conduction organic ceramic circuit board is prepared at a thermal conductivity of 9-20W/m.k under the condition of less than 250.The ceramic circuit board is an ideal packaging material for the new generation of large scale integrated circuits and power electronic modules with high thermal conductivity, good chemical stability and excellent thermal stability.In the near future, there are many ceramic circuit boards are used in high power LED heat dissipation substrates.However, LTCC / HTCC use thick film technology to prepare metal lines, making line accuracy is not very high, and limited by process factors, it is not adapt small size PCB.Therefore, the process capability of LTCC / HTCC is not suitable for small size and high power products at present.On the other hand, DBC is also limited to technological capability, and line resolution is only suitable for 100~300um.And its capacity for mass production is limited by the air hole in the metal / ceramic interface. Consider ceramic circuit board line accuracy, material heat dissipation coefficient, metal surface evenness and metal / ceramic indirect overlap,The most widely applied category of DPC ceramic substrate is made of thin film micro film at present.

MCPCB is mainly evolved from the early copper foil printed circuit board (FR4).MCPCB takes the metal as the core technology, uses aluminum or copper metal as the substrate of the printed circuit board, and attaches a copper foil or copper plate on the substrate to improve the heat dissipation.Due to the good ductility and heat conduction of the aluminum metal itself and the high thermal conductivity of the copper metal, MCPCB is reasonable to have a very good heat conduction / heat dissipation effect.However, aluminum itself is a conductor,based on the product characteristics, an insulator must be insulated between aluminum substrate and copper to avoid the conduction of copper line and aluminum substrate.Therefore, MCPCB mostly uses polymer materials as insulating material, but the thermal conductivity of the insulating layer (Polymer) is only 0.2~0.5W/mK, and there is a problem of heat resistance.Therefore, the thermal conductivity of the aluminum / copper metal, which has excellent thermal conductivity, is formed after the addition of Polymer, which greatly reduces the heat conduction efficiency of the whole substrate,lead to thermal conductivity of MCPCB is only 1W/mK~4W/mK.In recent studies, high conductive materials were cladded to MCPCB polymer materials, although the thermal conductivity of MCPCB products was raised.But the thermal conductivity of the main axis of the MCPCB is only about 3~5W/mK,However, in practical application, MCPCB also faces metal extension due to the Stamping Division.At this time, the deformation of the metal copper layer is caused by the extension of the stamping deformation, which leads to the deformation of the polymer dielectric insulating layer at the edge of MCPCB,In this way, it is easy to make the pressure resistance of LED products unstable (dielectric polymer deformation and damage).

Posted on 27 Mar 2018
By info@kingsunpcb.com
In PCB knowledge

What Is The Best Quality PCB

All PCB board looks almost same from the surface.Through the surface we see differences, and these differences are crucial to the durability and function of the PCB board throughout life.

It is essential that the PCB board have reliable performance both in the manufacturing process and in the actual use.In addition to the relevant costs, the defects in the assembly process may bring into the final product failure during the actual use, resulting in a claim.Therefore, from this point of view, it can be said that the cost of a high quality PCB is negligible.

The application of PCB board involves the fields of automobile, power supply, medical treatment, industrial control, security and even military industry.Like automobile engines, medical equipment, military workers and even aviation equipment, if the PCB board fails on these products, it may endanger human being and state.

These aspects should be keep in mind when compare PCB price,Although the initial cost is higher for reliable, guaranteed and long life products, it is still worth in the long run.

The most important 9 features of a high quality PCB:

Copper thickness of hole wall at 25 microns

Benefits: enhance reliability, including improving the ability to resist expansion of the Z axis.

The risk of not doing this: the problem of electrical connectivity (inner separation and hole wall fracture) in the process of blowing holes or degassing or assembling.Or in actual use, there may be a failure under the load condition.

No welding repair or circuit repair

Benefits: a perfect circuit ensures reliability and safety, no maintenance, and no risk.

The risk of not doing this: if it is not properly repaired, it will cause circuit open.Even if “proper” is repaired, the risk of failure in the load condition (vibration and so on) may cause a failure in actual use.

Cleanliness requirements beyond the IPC specification

Benefits: improving PCB cleanliness can improve reliability.

The risk of not doing this: the residue on the circuit board and the accumulation of solder will bring risk to the welding layer,Ion residues can lead to corrosion and pollution risks of welding surfaces, which may lead to reliability problems (bad solder joints / electrical failures).And ultimately increase the probability of failure.

The tolerance of copper clad meets the requirements of IPC4101ClassB/L

Benefits: the strict control of the dielectric thickness can reduce the expected deviation of the electrical performance.

The risk of not doing this: electrical performance may not meet the requirements, and the same batch of components will have a large difference in output / performance.

Soldering materials to ensure compliance with IPC-SM-840ClassT requirements

Benefits: ensure the safety of the ink and ensure that the solder layer inks conform to the UL standard.

The risk of not doing this: poor quality ink can lead to adhesion, flux resistance and hardness problems.All these problems will lead to soldering layer peel off from the circuit board and eventually lead to corrosion of the copper circuit.Poor insulation can cause short circuit due to accidental electrical connectedness / arc.

Tolerances of shape, hole and other mechanical characteristics

Benefits: strict control of tolerances can improve the quality of the product – the improvement of fit, shape, and function.

The risk of not doing this: problems in the assembly process, such as alignment / coordination (only when the assembly is completed) can be found. In addition, as the size deviation increases, the installation of basement will also be problematic.

Thickness of soldering layer

Benefits: improving the electrical insulation characteristics, reducing the risk of peeling or losing adhesion, and strengthening the ability to resist mechanical impact, no matter where the mechanical impact happens.

Requirements for appearance and repair requirements

Benefits: carefully nurture and carefully cast safety during the manufacturing process.

The risk of not doing this: a variety of bruises, minor injuries, repairs – the circuit board can be used but not good. In addition to the problems that the surface can see, what are the risks that can not be seen, the impact on the assembly, and the risks in actual use?

The depth of vias plugged requirement

Benefit: high quality vias plugged will reduce the risk of failure in the assembly process

The risk of not doing this: heavy chemical residue in the vias of uncompleted filling , resulting in solderability problems.But the hole may also be in possession of solder ball, assembly or actual use, solder may splash out, causing a short circuit,also may solder ball hide in vias and splash out when in use causing circuit shot.

Posted on 23 Mar 2018
By info@kingsunpcb.com
In PCB knowledge

PCB Backdrilling Technology

What is backdrilling?

In the high speed signal transmission printed circuit board, part copper of vias becomes the signal transmission”tail” (Stubs),adverse effects on signal transmission,in order achieve better signal integrity, it is necessary to reduce the length of the Stubs in vias,shorter length of the residual Stubs is better for integrity of the signal.

Backdrilling is the way to remove PTH and Stubs without any connection or transmission in vias by the second drilling.This Stubs will distort the signal caused by the reflection, scattering, delay, etc. of the signal.

Difficulties in backdrilling technology

Back drilling depth control

The backdrilling is the processing of blind holes by the depth control function of the drilling machine. The tolerance is influenced by the precision of the drilling equipment and the tolerance of dielectric thickness.Besides, its accuracy is easily influenced by external factors, such as the resistance of drilling tool, the angle of drill tool tip, the contact effect between the cover plate and the measuring unit, the bow and twist of PCB, etc.Therefore, more attention should be paid to selecting more suitable drilling materials and drilling methods to control the accuracy to the best.

Precision control of backdrilling

The back hole is formed by the second drilling afer first drilling, and the accuracy of the second drilling is critical.PCB material harmomegathus, precision equipment, drilling, drill size will affect the accuracy of the second drilling,it’s very importance to the quality control at end process of PCB manufacturers.

The backdrilling capability of King Sun PCB

King Sun PCB has accumulated rich technical experience for many years backingdrilling process.Its technical ability has been in the forefront of the industry. The next figure is a 16 – layer five deep – back drilling technology, with a depth control tolerance +/-0.05mm.

Posted on 21 Mar 2018
By info@kingsunpcb.com
In PCB knowledge