PCB Tech - PCBA technology's welding strength of electronic parts

The following is an introduction to the welding strength of electronic parts of PCBA technology

In the article about the structure analysis of the Micro-USB connector, I suddenly remembered an interesting soldering concept that I can discuss with you in this article.

The metal shell welding foot length of the Micro-USB connector is usually only 0.8mm long, because the thickness of the mobile phone board is about 0.8mm ~ 1.0mm, but the thickness of the PCB company board is 1.6mm, and the SMT factory uses Reflow to solder the Micro-USB connection After the device, it is often found that the solder in the through holes of these metal shell solder feet is almost not 100% filled, and some are even only about 70% filled. The non-filled part in the inspection hole is about 0.3-0.5 mm depth, will it affect the welding strength of Micro-USB? Can the PCB factory be required to fill these through-holes with tin or let it protrude from the surface to strengthen the soldering ability?

As soon as our RD encountered a problem of parts falling, the first reaction was to come to us and ask the PCB factory to increase the solder strength! Are we too easy to discuss, or...

When encountering such a problem, Shenzhen Grand Power will usually ask the other party to bring the defective Micro-USB and assembled circuit board to Shenzhen Grand Power for inspection. Almost every time the Micro-USB connector is removed from the circuit board. Falling down, because the company will do plug-in test and drop test for this kind of connector, so there will be this kind of trustworthiness to be solved.

After inspecting these dropped parts and the assembled circuit board, it was found that the solder on the other side of the through-hole of the metal shell of the Micro-USB connector was not cracked, so even if the solder paste is completely filled in the through-hole, Do the same test again, the Micro-USB connector will still fall off. This is like burying a telephone pole in the soil, and then a sudden typhoon blows the utility pole down, but blames the soil under the pole. Not enough, so the telegraph pole will collapse is the same reason. The problem should be that the poles are not buried deep enough, or the typhoon is too big! It shouldn't matter how much dirt there is under the poles.

So what can we do to reduce the chances of telegraph poles being blown down by a typhoon?

1. Bury the telegraph pole a little deeper.

2. Add other supports beside the poles.

The above two points should be solutions that we can actually see, so smart you should already know how to strengthen the ability of the Micro-USB connector to withstand plugging or dropping!

1. The PCB supplier is required to make the soldering feet of the metal frame longer (the pole is buried deep). This depends on whether your company's product volume is so large that the supplier is willing to help you make a special Micro-USB connector with extended solder feet. It depends on the thickness of your company's PCB.

2. Use other mechanisms outside the Micro-USB connector to prevent the possibility of being pushed away (add other supports next to the poles). The usual method is to add an iron frame outside the original Micro-USB connector, and then stuck it on the mechanism of the circuit board, or use other stronger mechanisms on the product to withstand the Micro-USB connector.

Many friends have misunderstood the welding strength. The notion that "the more the amount of solder, the stronger the welding strength" is not completely correct. Please correct the notion that "welding strength is proportional to the area of the welded parts", and do not consider replacing it. In the case of surface treatment of solder paste and circuit boards, there are two main points to enhance the welding strength of parts:

1. Increase the contact area of solder. It's not volume! Therefore, a large mass of solder is added, and the strength is almost the same as that of filling the solder pins with tin. If you look closely, you should see that most of the Micro-USB connector suppliers make a fuss on the soldering feet of the metal shell. Some punch holes on the soldering feet, and some increase wrinkles. The purpose is to increase the soldering tin. Contact area to improve welding strength.

2. Use structural design to transmit the force to other institutions to withstand it. The most common thing is to make the pins of the Micro-USB metal shell into an upright perforated design, so that the force can be transmitted to the PCB hole wall to withstand it.