About the Electroplating

Quick Summary

Electroplating can be divided into to kinds: Plated through hole and copper plating. Plated through hole (PTH) steps are applied after holes are drilled on the double layer PCB. The purpose is to metalize the resin and glass fiber of the non-conductor part of the hole wall for the subsequent plated through hole process, so that the metal hole wall that is sufficiently conductive and welded is completed. In addition to conventional PTH, direct-plating is also another option to adopt.

There are various kinds of problems when it comes to electroplating, each of which involves a considerable scope. Factors such as solution, equipment and human factors can all have great influence, making it hard to identify problems. Related disputes thus arise at later stages of the process. So, how to determine if the abnormality resulted from the electroplating process itself? This text is going to explain it through different categories to help you identify the problems.

Electroplating Case Introduction

Analysis of PTH Quality Problems

PTH Void

The so-called void of a PCB means the breakout, crack, dent or lack of copper of the copper which is supposed to be flawless during or after the metallization of the hole wall.

The shapes and the factors of PTH voids can be divided into:

1-1. Voids caused by poor de-smear

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Poor vertical sectioning NG
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Poor vertical sectioning NG
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Poor horizontal sectioning NG

There is still smear which is not fully removed between the inner copper ring and the hole wall in the pictures above, causing black voids that will easily lead to poor interconnecting between the annular ring and the copper wall, resulting in open-circuit when pulled away in the subsequent high temperature process.

1-1. Voids caused by over de-smear (excessive drilling roughness)

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It’s usually hard to tell the difference between the chemical corrosion caused by over de-smear and the one caused by excessive drilling roughness. De-smear means the process of reducing the bond energy of the resin with the leavening agent, making the potassium permanganate corrode the resin with strong oxidizability and further forming small holes for electroless copper plating. Over de-smear leads to cellular glass fiber protrusion with neat breakpoints, and such defects are called “wicking.” The left image is caused by over de-smear, while the right image is the small breakout caused by drilling.  

Voids caused by poor de-smear

Cause analysis:

A.Low temperature or concentration of the leavening bath solution.
B.Low temperature or concentration of the de-smear bath solution.
C.Leavening agent or de-smear agent immersion for too long or for too short a time.
D.Reactive ingredients in the substrate or poor solidification.
E.Poor regenerative system, poor drilling condition, or drill pin poorly polished.

Improvement measures:

A.Adjust the temperature or the concentration to the normal range.
B.Confirm the immersion time.
C.Reduce the time and temperature of the potassium permanganate, and enhance the substrate baking.    

1-2. Voids caused by poor backlight

The picture above shows the voids caused by poor backlight. Whether the backlight is good or not influences the quality of copper plating. Generally speaking, the backlight should be controlled at Grade 9 or above. For actual production, it’s even better to be controlled at a minimum grade of 9.5.

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During the production, one should pay particular attention to the loading amount (generally 0.8–1.2 dm2/L) so that it won’t lead to insufficient activity of electroless copper plating because the amount isn’t enough. Whether the activity of copper plating is enough can also be identified by observing the changes of color of the copper plating bath solution during the production. Usually, when the bath solution color is light blue, it means the activity is fine. Deep blue means that the activity isn’t enough, while black or deep black means the bath solution is abnormal and has aged.

Cause analysis:

A.Insufficient immersion time of electroless copper plating.
B.Low temperature (lower than 20 °C) of electroless copper plating.
C.Low deposition rate (lower than 15 μin) of electroless copper plating.
D.Low concentration of activator.
E.Low temperature of activator tank.
F.Low concentration of accelerator.
G.Low temperature of accelerator tank.
H.Activity of copper plating tank too low to start the plating after stopping the line.     

Improvement measures:

A.Adjust the immersion time appropriately.
B.Check the temperature controller and heating pipes.
C.Adjust the electroless copper plating formaldehyde (HCHO) to a higher concentration.
D.Adjust the concentration to the set point.
E.The loading is generally controlled at 0.8–1.2 dm2/L.
F.Control the plating start process after stopping the line.
G.Check the vibrating device and pneumatic device.

1-3. Voids caused by incomplete solution

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Good hole wall is the key to good electroless copper plating, but if the chemical solution itself is out of balance, no matter how well the hole wall is formed, it’s of no avail. Generally speaking, air bubbles and plug holes are not commonly seen in the big holes. The only reason might be poor activating or a bad electroless copper plating reaction, so the control of the electroless copper plating rate is rather important.

Cause analysis:

A.Poor activating.
B.Bad electroless copper plating reaction (too fast or too slow).

Improvement measures:

A.Adjust the activation parameter appropriately.
B.Adjust the electroless copper plating parameter.

1-4. Voids caused by air bubbles

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Main Features: When the length of panel plating is symmetrical, the pattern plating covers the panel plating, and the corner of the pattern plating doesn’t obviously become thinner and has a curved shape while no wicking is found, it can be judged as PTH air bubbles voids.

Cause analysis:

A.Abnormality in vibrating motor (insufficient vibration).

B.Abnormality in the basket (serious breaks in the basket), or no fix between the son basket and mother basket

C.Abnormality in the rack (there’s no hook behind the rack to combine with the basket, which causes a bigger amplitude of fluctuations during the vibrating process, invisibly reducing the amplitude of the vibration in the board and thus failing to remove air bubbles).

D.Lay up during the PTH production process (the boards are rather thin and not used along with the specialized thin board frame, so lay up occurs due to fluctuation, vibration and air agitation, which further impacts the penetration ability and the bubble breaking ability of the solution ).

E.Insufficient fluctuation or under inflation.

F.High aspect ratio that leads to poor throwing power.

Improvement measures:

A.One should check if the vibrating motor operates normally before the production, and regularly perform fluctuation tests on it. The general fluctuation is controlled at 0.2 mm–0.4 mm. (Note: For boards with a high aspect ratio, to ensure its good throwing power, the fluctuation has to be controlled at the upper limit. But at this time, whether the basket can take it must be taken into account).

B.One should check the basket for the production to avoid the hitch point of the rack from breaking and further failing to achieve the “vibration” effect. It is suggested that 2–3 baskets be additionally prepared as backups.

C.Boards with a thickness of ≤ 0.8 mm should be used with the specialized thin board frame; if there’s no specialized thin board frame, ordinary racks can be used by being inserting boards alternately, leaving a free space in between. However, during the production process, the activity of the electroless copper plating tank must be taken into account, and whether the area of the production board is enough

D.Install ultrasound device for the activating and conditioning.

E.Check if the fluctuation device, inflation device, vibration and pneumatic are normal.

F.For boards with a high aspect ratio (boards too thick with small hole diameters), one can use racks for PTH by inserting them alternately (i.e., leaving a free space in between). However, whether the loading capacity is enough and whether the activity of the electroless copper plating tank is sufficient should be considered.

G.Install pneumatic devices in the three tanks: conditioning tank, activating tank and electroless copper plating tank.

H.Consider if horizontal electroplating can be adopted.

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