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PCB Tech
Solutions to the top ten common defects in PCB punching
PCB Tech
Solutions to the top ten common defects in PCB punching

Solutions to the top ten common defects in PCB punching

2021-11-08
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Author:Downs

With the improvement of the quality of electronic assembly technology and the needs of market competition, fully automatic inserting machines have been rapidly popularized. In this way, the requirement for punching quality of single-sided PCB paper-based plates (a few single- and double-sided non-metallized epoxy-glass cloth substrates also use punching) is getting higher and higher. As far as PCB manufacturers currently produce and use fully automatic insertion machines, the complaints and return rates related to punching quality have risen to the first place. This article mainly introduces the top ten common defects of PCB punching and their solutions, including burrs, bumps around the opening of the copper foil, upward turning of the copper hole of the orifice, layered whitening around the opening of the substrate, and tilt and deviation of the hole wall. Position, rough section, cracks between holes and between holes, bulging shape, jumping up of scraps and blockage of scraps, etc., please follow the editor to learn more about it.

 One, glitch

cause

The gap between the concave and convex molds is too small, causing cracks to occur on both sides of the convex mold and the concave mold without overlapping, and two extrusion shears occur at both ends of the section.

The gap between the concave and convex molds is too large. When the convex mold descends, the cracks occur late, and the shearing is completed like a tear, causing the cracks to not overlap.

pcb board

The cutting edge is worn or rounded and chamfered, and the cutting edge does not play a role in the division of the wedge, and the entire section produces irregular tearing.

Solution

Reasonably choose the blanking gap of the concave and convex dies. Such punching and cutting are between extrusion and stretching. When the punch cuts into the material, the cutting edge forms a wedge, causing the sheet to produce nearly linear coincident cracks.

Refurbish the fillet or chamfer produced by the cutting edge of the concave and convex molds in time.

Ensure the vertical concentricity of the concave and convex molds to make the fit gap uniform.

Ensure that the mold is installed vertically and smoothly.

2. Bulging around the opening of the copper foil

cause

The blanking gap between the concave and convex dies is too small, and the punch edge becomes blunt. When the punch is inserted into the preheated and softened printed board, the plate will squeeze and move outwards and upwards around the punch.

The punch edge has a taper. When the punch continues to enter the plate, the bulging around the orifice will increase as the taper of the punch increases.

Solution

The blanking should exceed 20% of the original design thickness; otherwise, replace the plate or redesign the die.

The blanking should have enough pressing force to overcome the back-squeezing force of the material movement when punching;

Third, the copper port of the orifice is turned up

cause:

Due to the backlash, the copper foil is drawn into the punching gap of the concave and convex dies.

The bonding force between the copper foil and the substrate is poor. When the punch is pulled out of the printed board hole being punched, the copper foil is pulled up with the punch.

There is an inverted cone at the edge of the punch, which is swollen and deformed. When the punch is pulled out of the hole of the printed board, the copper foil will be pulled up with the punch.

Solution:

Use positive impact.

Replace the punch.

The clearance between the punch and the discharge plate should not be large, and a sliding fit should be used.

 Four, the layered whitening around the opening of the PCB substrate

cause

The blanking gap between the concave and convex dies is inappropriate or the cutting edge of the concave mode becomes blunt. When punching, it is difficult for the punched sheet to form shear cracks at the edge of the concave pattern.

Substrate blanking performance is poor or not preheated before blanking.

The pressing force is small.

The leakage hole at the lower part of the die blade is blocked or the leakage resistance is large, resulting in expansion and stratification.

Solution:

Reasonably expand the blanking gap between concave and convex dies;

Repair the blunt die cutting edge in time;

Increase the pressing force;

Adjust the preheating temperature of the substrate;

Enlarge or ream the leakage hole

Five, hole wall tilt and offset

cause

The punch has poor rigidity, unstable centering, and tilts into the workpiece.

The installation of the punch is inclined or the clearance with the unloading plate is too large, and the unloading plate cannot provide precise guidance to the punch;

The gap between the concave and convex molds is uneven. On the side with a small gap, the punch will receive a large radial force and slide to the side with a large gap; 4). The concentricity of the concave and convex mode assembly is poor; the shape of the pusher plate and the concave and convex molds are offset; the precision of the pusher plate and the concave mold is too poor (referring to the compound blanking).

Solution:

Choose the material of the punch reasonably; improve the rigidity, strength, hardness and unevenness of the punch.

Improve the processing concentricity and assembly concentricity of the punch and the die.

Improve the matching accuracy of the punch and the discharge plate to ensure precise guidance.

Ensure the processing accuracy and assembly accuracy of the guide post and the guide sleeve; reduce the matching gap between the shape of the pusher plate and the concave die, and make the shape of the pusher plate consistent with the concave-convex shape.

Sixth, the PCB section is rough

cause

The blanking gap between the concave and convex dies is too large; the cutting edge of the concave die is severely worn.

The punching force of the punch is insufficient and unstable. 3). Sheet blanking performance is poor. For example, the base material contains too much glue, the base material, aging, and the lamination bonding force is low.

Solution

Choose the appropriate blanking gap between the concave and convex dies.

Trim the cutting edge of the die in time.

Select PCB substrates with better blanking performance and strictly control the preheating temperature and time according to the process requirements