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How to analyze printed circuit board component drop

436 Published by FASTPCBA 11月 23,2018

How to analyze printed circuit board component drop

Printed circuit board component drop seems to be a pain point for many manufacturing process and quality control engineers, but everyone has different problems, in view of many people encounter this kind of problems do not know how to start analysis, so here to share some methods and steps for your reference.

printed circuit board assembly

printed circuit board assembly

Generally, if PCB parts fall off, most of the problems cannot be separated from the welding quality, and the final answer is nothing more than one of the following, or a mixture of more than two results:

There is something wrong with the surface treatment of the board.

There is something wrong with the surface treatment of the welding foot of the parts.

Poor storage conditions of plates or parts cause oxidation.

There is something wrong with the Reflow temperature process.

The welding strength can not withstand the actual use of external force.

Several steps of printed circuit board parts falling bad analysis:

The following is an analysis of the steps to describe the falling parts of the shop floor board, because it is necessary to divide some actions into steps, but some steps seem to be related to other steps.

pcb printed circuit board

Step 1:The information obtained

This is very important, if the source is wrong, later how wonderful is in vain.

Please first confirm the description of adverse phenomena to the problem responder, and first try to query the following information:

What’s the problem?Please try your best to describe the bad phenomenon clearly.Under what circumstances did the part fall off?Have you ever dropped the product?Under what circumstances (gas station, outdoor, indoor, air conditioning)?Have you passed any special tests (high and low temperature)?

Is the problem on the client side?Is it in production?At which step in the process does the problem occur or occur?

When did the problem arise?Is it found in the production process?Or did you find out when you were testing the finished product?Are defective products concentrated in the same date-code?

What is the surface treatment of the board?ENIG?OSP?HASL?ENIG will have a black nickel problem, HASL will have a second tin-over problem, OSP will have a tin-over problem.

The thickness of the board?0.8 mm?1.0 mm?1.2 mm?1.6 mm?The thinner the plate, the greater the chance it will bend and crack.

What is the surface treatment of the welding foot of the part?Matte enrolled Tin?Gold plated?

What is the main ingredient of tin paste?SAC305(tin silver copper)?Student: SCN?Different solders have different melting points.

The reflow measurement curve at that time is the best if it can be recalled.

Step 3:Obtain defective products and retain evidence for subsequent analysis

Please get the printed circuit board of defective products. If the parts have completely dropped off, it is better to get the dropped parts, so that the control group can make a complete analysis.If you have more than one defective product, you can measure the actual situation and get as many as possible.

Step 3: check the solderability of printed circuit board

After getting the defective products, check the solderability of printed circuit board and parts feet at the same time, and observe the difference between them.When checking the solderability, it is suggested to observe under the microscope, so that we can see some microscopic problems.

Step 4: check the solderability of the dropped part foot

It is also recommended to observe the solderability of parts’ feet under a microscope, so that you can see some subtle phenomena that cannot be seen by the naked eye.

To check whether the parts feet eat tin is good, it is recommended to check the coating composition of parts feet, see whether the melting tin temperature is consistent with the temperature of the back welding furnace.Some parts with silver coating splash plating treatment, the splash plating of silver is only attached to the surface of the parts, the silver component is easy to be eaten SAC tin paste, resulting in the problem of reduced welding strength.

Please note that the cutting surface of some parts’ feet will have areas exposed to copper without electroplating, which is usually not easy to eat tin, but is generally designed in places that do not need to eat tin or are not important.The QFN side doesn’t have to eat tin.

printed circuit board assembly

printed circuit board assembly

 

Step 5: check whether the foot of the dropped part is taken together with the welding pad

If there is no problem with the solderability of printed circuit board and part foot, it is necessary to check whether the welding pad/pad on PCB circuit board is also detached or attached to the dropped part foot. If so, it can further confirm that the welding between the part and PCB is good, and it can also prove that Reflow is ok.

If the welding pad is not taken away with the dropped parts, at this time, you can first check whether the temperature curve of the back welding conforms to the requirements of solder paste. If there are any excess defective products, it is better to try with a soldering iron to see whether the dropped parts can be welded back to the printed circuit board.Represent temperature welding have to go back if you can, or solder paste can strengthen to overcome this problem, but it is suggested to make the parts of the thrust test, and confirm there is no problem of the board, and readjust the solder paste now and temperature curve of the board, thrust compared with presence of differences, if there is a difference, suggest to check the PCB surface treatment, surface treatment sometimes bad, can cause the welding pad oxidation, ENIG surface treatment may have black pad problem, the second HASL surface may have a problem of IMC has been generated.

Step 6: check the section where the parts fall off

Please observe the dissection surface of printed circuit board and part foot under microscope to see whether its section is rough or smooth.Rough surface is usually subjected to a one-time external force caused by the parts shed;Smooth surfaces are usually broken by long periods of vibration, and ENIG PCBS can also flake on the nickel layer due to black nickel.

Step 7: slice IMC and EDX

If there is no way to judge the part falling problem in the above steps, the destructive slicing will be done at last. It is recommended to do both printed circuit board and the dropped parts when slicing.

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