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How to do a good job in the protection of PCBA proofing chip components
- 2020-01-30-

With the technological development of electronic products, circuits are becoming more and more dense, the number of components on a single board is increasing, and the risk of damaged parts increases accordingly. In this article, it is explained in detail how to standardize the operation in the PCBA proofing and patching process to avoid the occurrence of damaged parts.

Operational problems causing collisions

In-process damage-impact fracture, stress damage

1 The thimble is set improperly

The support in the immediate vicinity is destroyed when the bending stress is applied to the component or the test is implemented.

The damage feature of the resistor is fracture or electrode peeling, and the capacitor is the inclined crack mode. If it is the first process part, the tombstone phenomenon of the fractured part may be seen after reflow.

如何做好PCBA打样贴片元件的防护

2 stress damage

Poor board feeding causes deformation of the splint (card board) or manual bending of the board; poor suction nozzle and improper height setting can cause damage to the set.

The typical feature of PCBA proofing patch damage is frontal cracking, and the fracture is usually separated after passing the furnace; if it is side damage, the chamfered slope is mostly cut off. Under this condition, the location of the impact point can be clearly distinguished.

Operational problems causing collisions

Damage after the process-impact rupture,

Stress damage, layer peeling (thermal shock)

1 impact rupture

PCBA proofing patch is usually not easy to judge the impact point in lateral impact, because the PAD is usually peeled off (resistance) or the part electrode has broken (capacitance); and the longitudinal impact part is easier to identify the impact point, and the PAD is generally not damaged but the parts can be seen To the obvious missing corner.

2 stress damage

Damage caused by pressure and bending due to the folding of the edge of the plate, the test fixture, the placement of the trolley, etc. This type of damage usually appears in the form of an inclined crack.

3-layer peeling

Caused by improper welding repair. Typical characteristics are burnt black FLUX near the part, rough surface discoloration, layer peeling (capacitance), character surface peeling, etc.

How to start analyzing damaged parts

1 According to the point of impact analysis

The presence or absence of an impact point is not an absolute analysis and judgment factor, but usually the location, direction and damage degree of the impact point will provide a lot of analysis information.

a. The straight impact force usually causes damage to the PCB, and obvious damage defects can be seen on the components.

b. Parallel impact force will directly cause damage to the part due to cracking and missing corners, but because the direction of the torque is not large, it will not cause serious damage to the PAD most of the time.

2According to the crack shape

a. Delamination cracks: Most of the causes of delamination are due to thermal shock, but part of the reason is poor component manufacturing, because the layer-to-layer bonding and Baking process defects cause delamination after reflow.

b. Oblique cracks: Because the bending stress forms a fulcrum at the lower part of the part, the fixed solder joint produces a cracked oblique surface phenomenon at the electrode end, especially the large-size component perpendicular to the stress direction is most severely broken.

c. Radial cracks: Radial cracks generally have impact points to follow, mostly caused by point pressure, such as thimble, suction nozzle, test fixture, etc.

d. Complete rupture: Complete rupture is the most serious failure mode, and it is often accompanied by PCB damage. It is usually caused by lateral impact or capacitor cracks causing component burnout.

3 According to the displacement of the parts

When PCBA proofing patch parts have longitudinal cracks or reflow heating but not broken, it is very likely that only the cracks will be seen but there is no separation, which will cause inspection troubles. The cracks that have been caused before reflow will be pulled apart due to the tensile force of the melting of the solder, and even in the back side process, there will be tombstones at the fractured parts. Most of the causes are damage to the components in the first process, bending stress or improper setting of the ejector pins in the second process. Of course, cracks caused by cutting and packaging in the component manufacturing process may also be broken by heat after reflow.