With the development of modern industry, there are more and more projects need to use flexible circuit, and the requirements of assembly are getting higher and higher.
In the Flex Printed Circuit(FPC) typical production process, normally we will finish the entire flexible PCB production process, and then arrange to solder components. But such a finished product, components exposed, it can not pass the waterproof test. Our traditional waterproof process is to cover Silicon or conformal coating.
Our engineers decided to change the production process after discussion. For new technology,
The first step is trace Etching;
Second step is surface treatment (normally is ENIG (Electroless Nickel/Immersion Gold);
Third step is component assembling;
flex circuit with component stackup
The Forth step and the most important step is making the pure adhesive between base material and coverlay, we need to laser cutting or punching the cutout above the area of component, so that there’s no extra adhesive in that area and then the total thickness of that area will no be too high.
flex circuit with component stackup2
And you can see the full picture showing step 3 to step 4 of flex circuit components making.
flex circuit with component stackup
After that, we put the Polyimide on pure adhesive and then go the next step of lamination process. (To laminate the coverlay on the surface of component.).
You can see below pictures.
flex circuit with components
flex circuit with components details
You can visit our website or send us your email if you would like to know more about flex printed circuit.
How to deal with these situation?There have glue mark and greasy dirt on the boards in prepared processing stage, it need to clean the plate thoroughly.
The temperature is too high and time is too long in the stage of Pre-heating, so it need to control the temperature of the pre-drier, adjust it on normal temperature and strengthen the control of time.
The exposure energy is too high on the stage of exposure, or the shading rate is poor of the base boards.
The developing liquid’s concentration and the temperature are too low, so it need to check the concentration and adjust the temperature to normal timing.
Differences between Roll Anneal Copper Foil and Electrolysis Deposition Copper Foil
Roll Anneal Copper Foil (RA copper):
Formation: Roll copper block many times, and then do the annealing treatment with high temperature. The shape of its crystal is lamellar structure.
Advantage: Soft, smooth surface, suitable for flexible PCB and small lines.
Shortage: high cost
Electrolysis Deposition Copper Foil (ED copper):
Formation: Melt copper into dilute sulfuric acid, it becomes bluestone solution.
Through a high electric field, copper attach on the metal drum. With the rolling of metal drum, thin copper foil finally formed.
Advantage: Low cost
Shortage: Unsuitable for small lines; bad bending resistance.
Here is the cross section observation of RA Copper and ED Copper:
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…)
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 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
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.
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.