PCB Technical - The purpose of circuit board quality inspection

The purpose of circuit board quality inspection

1. Endoscopy
The operation and screen presentation of various existing assembly and reflow quality inspection machines
The quality of the various inner and outer balls of BGA/CSP after soldering with solder paste can not be inspected by top view magnification or microscopy, but the side-view light source and side view magnification can be used instead to check the inner and outer parts of the abdominal bottom one by one. The surface quality of the solder joints. When the light source and the lens only scan along the outer edge of the periphery, it is called a Rigid Endoscope; if the light source and the lens are reduced together and fitted into a slender steel tube, which can extend into the ventral base of the combined device, then Also known as Flexible Endoscope. For the solder joints that are difficult to access deep in the narrow space of the bottom of the abdomen, I was able to get a glimpse of it, and found a powerful tool for the non-destructive solder joint quality inspection of BGA/CSP.

The endoscope used in the electronics industry can not only observe the quality of the ball feet of BGA/CSP and other area array elements, but also the J-shaped hook with the inward sequence of the PLCC. The recently launched models can also observe the flip chip microscopically. The appearance of the tiny bumps inside the package is amazing!

The next-generation soft Endoscope under development will be able to focus on the built-in flip chip bumps in a variety of depths of field, and the range that can be seen clearly under its focusing conditions. For the deep solder joints, this This observation is very important. The slender optical hardware must not only be very precise but also very strong and durable. The supporting frame must not only facilitate the clear capture of images, but also protect the optical parts.

Second, the practicality of the scene
(1), the outer edge side view

Using the Rigid Endoscope hard side view microscope, you can see the appearance of the abdominal bottom of the BGA/CSP package components, that is, you can see the lack of quality of the ball on the package carrier and PCB surface. For example, bridging short circuits, micro cracks, splashed tin broken balls, flux residues, etc. can be inspected closely, but this kind of hard side-view microscope cannot inspect various conditions deep inside.

(2) Close view inside

The popcorn phenomenon of the carrier plate often occurs inside the bottom of the large BGA, but it is often mistaken for the lack of welding because it is difficult to observe and judge from the outside. Other poor quality such as tin splash and flux residue in the inner ball area has always been a thorny blind spot. As for the BGA-style high-priced CPU microprocessor after the PCB board surface is soldered, there are many decouplings in the central area of the belly bottom. It is also very difficult to determine the common small capacitors, such as tombstones and partial welding. Many of these problems require clear images that can be penetrated into the close-up view as a basis for relief and improvement. It's time for FME to appear on stage.

Operating conditions of a soft endoscope with a steel outer tube that can extend the eye

The soft FME probe tube (diameter 0.32mm), which is composed of a tiny fiber optic tube and a tiny lens, can be carefully inserted into the ventral base of the BGA/CSP after installation to obtain the desired picture. The current technology is not very clear. In time, there may be a new machine with better picture quality on the market. In addition to the optical quality, the durability of this kind of micro probe is also a challenge. The current method uses a steel capillary as a protective shell to reduce accidental damage during handling. A commodity FME, which is equipped with three IC-style digital cameras, uses xenon-type cold light source as illumination, and its steel probe tube has a wide diameter range of 0.28-1.0mm

In order to enhance the function of this exquisite endoscope, the supplier has made the FME into a modular and comprehensive model, using macro perspective, micro lens and special interface unit. With the assistance of other machines, you can get a tiny and dark picture through the command of the software and quickly change the optical lens to get a bright and clear image. This modular approach can not only increase the convenience of operations, but also reduce the cost.

3. Benefits for lead-free soldering of circuit boards
It not only has a great impact on the soldering work and PCB surface treatment, but also for the BGA/CSP components that cannot be soldered on the board surface, the characteristics of lead-free solder are not good and the operation is not easy. The maintenance of quality is even more difficult and difficult, which makes the visual inspection of the abdominal fundus more important than before. For example, when the surface tension of SAC305 is too large when melting, it not only causes the soldering angle to become larger and the solder reversion, but also aggravates the tombstone problem of small chip components, and the bad tin splashing also increases, and the interface is microcracked. Further deterioration, and other poor appearance quality, all require the assistance of a new type of endoscope for inspection. The previous quality inspection practices of the lead soldering era, the lead-free soldering generation can no longer continue to be fully effective. Especially after the accelerated aging of high and low temperature cycles, the inspection of the interface microcracks of the inner ball solder joints, the endoscope is even more indispensable.

The two new side-pointing microscopic magnifiers introduced in this article are not cheap when paired with special software. The basic equipment only costs 13,000 U.S. dollars, and the users themselves must have deep experience in lead-free soldering. In order to demonstrate the power of these new machines in QC.