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PCB Q&A: Heat, Copper, UL94 & Gold Finger | Gold Phoenix

Time: 2022-07-13 20:07:30

Q&A of PCB

This Gold Phoenix PCB Knowledge Center article answers common PCB questions covering heat dissipation, copper thickness, gold finger plating, pad spacing, and UL94 flame retardant ratings.

1. Will the quality and thickness of PCB affect the heat dissipation effect?

The heat dissipation effect is mainly affected by the circuit design, which determines how heat is distributed and dissipated.

2. What are the main reasons for board deformation and warping?

(a) Board deformation:

Circuit design issues, such as single traces or uneven distribution of traces
Excessive internal stress in the board

(b) Board warping:

Vias designed too close together; layers become loose after drilling
Insufficient microstructure roughness between layers, resulting in insufficient bonding force
The boards absorb moisture due to the environment during fabrication and storage

3. What are the available copper thicknesses, and how is the finished board thickness calculated?

Common copper weights discussed in PCB design include 0.5 oz, 1 oz, 2 oz, and 3 oz. General products use H oz. Applications with higher current-carrying requirements may use copper weights such as 1 oz or more.

The copper used is electrolytic copper with a purity of more than 99.9%.

The finished board thickness is calculated from the base material to the surface of the copper.

4. How is a PCB evaluated?

PCBs are commonly evaluated with reference to standards such as IPC-6010.

5. What is the minimum distance between a via pad and an opening pad? What is the minimum distance between opening pads to ensure the solder dam? What is a blocking point?

The minimum distance between a via pad and an opening pad should be greater than or equal to 4 mil.
To ensure the solder dam, the minimum distance between opening pads needs to be 7.5 mil.
A blocking point adds a solder mask block area in the center of the hole.

6. What is the normal thickness for gold finger plating?

A commonly referenced gold finger plating thickness is 2.54 µm nickel-gold, with a gold thickness of 0.5–0.75 µm.
Whole-board ENIG (Electroless Nickel Immersion Gold) surface treatment can also be selected, in which case the gold finger does not require additional plating. However, it is recommended to plate hard gold for boards that are frequently inserted and removed.

7. What are the fire rating markings?

UL 94 is the most widely used standard for the flammability of plastic materials. It is used to evaluate the ability of materials to self-extinguish after ignition. There are a variety of criteria, including burning speed, burning time, ability to resist dripping, and whether the drips continue to burn.

The flame retardant grades of plastics progress from HB, V-2, V-1, to V-0:

HB: The lowest flame retardant rating in UL 94. For samples 3–13 mm thick, the burning speed must be less than 40 mm per minute. For samples less than 3 mm thick, the burning speed must be less than 70 mm per minute, or the flame must self-extinguish before the 100 mm mark.
V-2: Flame extinguishes within 60 seconds after two 10-second combustion tests on the sample. Combustion drips are allowed.
V-1: Flame extinguishes within 60 seconds after two 10-second combustion tests on the sample. Combustion drips are not allowed.
V-0: Flame extinguishes within 30 seconds after two 10-second combustion tests on the sample. Combustion drips are not allowed.

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PCB Q&A: Heat, Copper, UL94 & Gold Finger | Gold Phoenix

Q&A of PCB