Normal Thickness for 2Layers Flex Circuit (Adhesiveless)

Following up with the last article , here we’d like to share thickness for 2L flex circuit if using adhesiveless material.

2L FPC Flex circuit thickness (adhesiveless)

2L FPC Flex circuit thickness (adhesiveless)

2L FPC thickness using adhesiveless material

We also have other special material, such as 1mil Polyimide + 2OZ (70um) copper adhesiveless, (from Dupont). If you need more information, please contact us.

Normal Thickness for 2Layers Flex Circuit (Adhesive)

Different from rigid FR4 PCB, there’re three basic layers for flexible circuits, and various thickness of each maybe used, so people new to that area will be confused to choose a suitable thickness.

Here are four normal thickness for 2 layers (Double sided) flex circuit, and we hope it’ll be useful for the green hand:-)

2L FPC Thickness

2L FPC Thickness

2L FPC Thickness

2L FPC Thickness

As you can see, there’re adhesive in base for each four basic thickness of 2L (double sided) flex circuits, if you need more thin, then you can use adhesiveless material, and final thickness will be thinner even you use the same copper and Polyimide thickness. Please see next article (to be continued…)

Solderability Test Experiment

As is well known, solderability is very important for the printed circuit boards, we must do solderability test of each batch PCB we made. In this way we can inspect the weldability of the PCB before we go ahead the assembly process, much helpful for SMT.

Today we are going to discuss the solderability test experiment. In order to explain it more clear, we now do a simple solderability test and show you all the steps.

1. Take a small solder pot, plug in the power, turn on the switch and heat the solder pot to a certain high temperature(about 8 minutes).

2. Put a tin bar to the solder pot, then you can see the tin bar is begin to melting, slowly into liquid tin, then more and more.
3. After few minutes, there will be enough melting liquid tin in the solder pot to do this test.
4.Use a tweezers to pick up a PCB circuit, first clean the PCB with rubbing alcohol. Because the unclear surface or the oxidation of the PCB will affect the test result.
5. This is the key step of this test, put the PCB into the solder pot, depth about 2 mm,time 4-5 seconds is ok. Then you can see the tin will go into the hole of the PCB.
6. Take out the PCB from the solder pot and put it into the cold water. After few seconds, you can see the experimental effect.

This solderability test is very simple and easy. We can see the results very soon. Our Best Technology did solderability of every batch PCB we made, and we also supply our customers with the solderability test report and the test samples.

Solderability Test

Solderability testing has become more common in the industry particularly to assess components and printed board surface finishes during the transition to lead-free manufacture. The wetting balance is the standard method of test and provides the repeatability that other methods do not.

Test Principle: Put the samples into tin bath, detect the solderability according to the hole wetting degree.
Ttest Purpose: Test the solderability of the PCB samples
Test Instrument: Thermostatic tin stove

Procedure:
1. Setting the tin slot temperature at 245℃, turn on the power.
2.Waiting for the Test Procedure up to 245℃+/-5℃, paint the samples with rosin. Use clamps nip it , just do as wave-soldering,let samples contact with the tin slot surface. Depth is about 2mm, time is nearly 4 seconds.
3. Tin material changing times: once / two weeks
4.Comments: The plated holes permit only 10% with half infiltrating, nonwettable and air blow is not allowed.


Figure 1. PCB samples before testing with the wetting balance



Figure 2. PCB samples after testing with the wetting balance.

As assembly Electronic components to printed circuit board always need high quality Interchange connection technology, doing the solderability test has great help to the high quality and zero defects welding technology. Our Best Technology did Solderability Test for every batch PCB, but due to some objective reasons, we didn’t give customers the solderability test samples. If customers need it, can also contact us.

The knowledge of printed circuit board via

                                     via

                                  The basic definition of via

As is known to all, via is one of the important parts of multilayer PCB. The cost of drilling usually makes up 30%~40% of the cost of PCB manufacture.

Simply speaking, every hole on PCB may be called via.

Functionally, via can be divided into two types: firstly, used for electro-connection among layers; secondly, used for fixing components.

Technically, it may also be divided into three types: blind via, buried via and though hole. Blind via is located on the top and bottom surfaces of the PCB, deep and used for connection of top traces with the inner layer traces below.

Buried via is the connecting hole which is located in the inner layer of the PCB and won’t extent to the surface.

Through hole goes through the whole PCB, which is used to realize inter-connection or used as components mounting position hole. Due to the simple technique and low cost, most of PCBs use it rather than the other two via.

The basic knowledge of PCB(3)

Today we will continue expanding some basic knowledge of PCB:

3. Components encapsulation technology

(1) Through hole technology

It means we mount components on one side, and solder the pins on the other. The disadvantage of it is space consuming. In fact, theirs pins take up space of both sides. While the advantage of it is good construction, which can bear pressure.

(2) Surface mounted technology
it means pins are soldered on the same side as components. We don’t have to drill holes  on PCB and don’t have to solder every pin. The advantage of SMT is that the components are more compact and cheaper than those in THT.

                                                smt2 

4. Gerber files:

Usually it comprises the layout plan of signal, ground, power, solder mask, silk screen, and drilling layout plan, etc.

                                          gerber file

5. Manufacture steps
choose base material, then use subtractive transfer to show the artwork on metal conductor.

The above explanation is only the most basic   information, if you want to know more, please to go our website: http://bestpcbs.com/products or contact me at Iris@bestfpc.com.

We are happy to help you clear all your questions!!!

The basic knowledge of PCB (2)

2. The classification of PCB

 (1) Single sided PCB

Single sided board means the conductor pattern appears only on one side. Because single sided PCB has many strict limits. On trace design, only circuit at early stage use this kind of boards.

(2) Double sided PCB 

Double sided board means the conductor patterns appear on both sides of the board. However if we use the conductor patterns on both sides, there should be proper circuit to connect two sides. The bridge between the circuits is called via. Those vias are plated with metal, such as tin, copper, gold, etc. Because the area of double sided PCB is two fold of the area of single sided, and the conductor pattern can cross with each other, so it suits to be used on more complex circuits.

(3) Multi-layer boards

In order to enlarge the area of conductor pattern, multilayer PCB uses more single or double boards. It uses several piece of double sided boards, and a dielectric layer is put between every layer of boards. The layers of one PCB represent the layer of conductor patterns. The amount of the layers is always even number. Technically we can make PCBs up to 100 layers.

 For via, if we use it on double sided PCB, the whole boards will be drilled. While on multilayer PCB, if you just want to connect some traces, via may will waste trace space of some layers. Then we use buried vias and blind vias to solve this problem, because they are only drilled through several layers.

a. Buried vias only connect inner PCBs, so we can’t see them from the surface.

b. Blind vias connects several layers PCB with surface PCB.

In multilayer PCB, the whole board directly connects the ground line and power (used for preventing affection of the transmission signals on the signal). So we divide layers into signal, power, or ground. If the components on PCB need different power supply, this kind of PCB would have more than two layers of power and wire layers.

 mpcb-22ss-web missionstatement  

 

mcpcb-1ss-web

How to calculate the thickness of FPCs

As is known to all, the FPCs are divided into single layer, double layers, dual access, multiayer and flex rigid.

Now I want to introduce the basic method of calculating the thickness of FPCs.

(!) single sided FPC

The constructure of single layer FPC is as follows:the board thickness for single sided FPC

25um+20um+35um+20um+25um=125um≈0.12mm

Note: the thickness of adhesive changes according to the thickness of Cu. For 1/2, 1/3 OZ Cu, we usually use 12um adhesive. But for 1OZ Cu, we have to use 20um adhesive.

That’s according to the common material. If we want the board to be thinner, we also can use the adhesiveless material to make the board about 0.8mm thick.

(2) double sided FPC

Double sided FPC means there are two layer of traces in the FPC.

The constructure of double sided FPC is as follows:

the board thickness for double sided FPC25+12+35+12+25+12+35+12+25=193um≈0.20mm

The advantages and disadvantages of FPC

A: Disadvantages:

1. Original cost is high

Because the FPC is designed and made for special application, the cost of circuit design, wiring and photographic plate is high. Except special need, we’d better not use them.

2. The modification and correction is difficult

Once FPCs are made, if we want to modify, we have to begin from the base drawing or gerber program. Therefore it’s difficult to change. On its surface there is a coverlay. Before the modification, we have to remove it, after the modification, we have to recover it, which is difficult.

3. Dimension limitation

Since FPC is not popular, we usually use intermittent method to make them. Then we can’t make too long or wide FPC with the limit of manufacture instruments dimensions.

4. Easier to be damaged if improper operation

It is easier to cause the damage of FPC circuits because of improper operation. Special trained workers are needed in tin plating and rework

 B: Advantages

FPC is the printed circuit board which is made of flexible insulating base material. It has many advantages many rigid PCBs don’t have.

1. It can be bent, rolled, folded freely, can be arranged randomly according to the space, can be moved and stretched in 3-D space, then integrate the components assembly and wiring connection.

2. It can satisfy the need of electronic products to develop in the direction of high density, smaller size, higher reliability, since FPC can greatly reduce the volume and weight of electronic products. Therefore FPC is widely applied in fields or products of aerospace, military, mobile communication, laptop, computer exterior design, PDA, and digital camera.

3. FPC also has the advantages of good thermal diffusivity and solderability, easy to assembly, low combined cost. The design of rigid-flex boards also make up the disadvantage of components carrying ability of flexible base material.

The structure, technique and design of FPC (1)

As more and more clamshell phones come into market, the FPCs are more and more used.

 According to the combination ways of the base material and the copper, the FPCs can be divided into two kinds: adhesive FPC and adhesiveless FPC.

 The price of adhesiveless FPC is much higher than the adhesive FPC. However it is superior to FPC in the aspects of flexibility, boning force of copper and the base material, and the flatness of soldering pad. Therefore generally it only is used in the occasion of high demand, such as COF (chip on flex, to mount exposed chips on FPC has high requirement of the soldering pad flatness).

 Due to adhesiveless FPC’s high price, at present most of the FPCs applied at the market are adhesive.

 Because the FPC is mainly used at the occasion of bending, if the design or technique is not proper, defaults such as micro-crack, snap of the welding point will be easy to arise. I will introduce the structure of FPC and its special requirements on design and technique.