Via local copper thickness is too thin and too hole open PCB manufacturing industry faced together, one of the major technical issues in the past the right hole open discussion and the research articles are limited in the PCB board system selection of plank, sheet for the CTE of thermal expansion coefficient is larger, later in the assembly of cold and hot shock caused hole cracking failure case analysis, such as copper processing without from the PCB itself, Hole copper electroplating to analyze and solve problems. This paper analyzes the cause of copper thin in the hole from the aspect of PCB electroplating, and tells us how to avoid PCB failure caused by open circuit due to copper thin in the hole from the aspect of electroplating.

Generally speaking, most of the hole copper thickness of the traditional circuit board is required between 0.8-1mil. As for some high-density circuit boards, such as HDI, because the blind hole is not easy to electroplate and in order to make thin wire, the requirements for hole copper thickness will be moderately reduced, so there are also minimum finished hole copper thickness of 0.4mil or more specifications. However, there are some special cases, such as large circuit boards for systems that require a hole thickness of 0.8mil or higher because of the special assembly and reliability requirements for long periods of use. In IPC-6012, there is a clear grade of copper thickness in the face of the hole, so what kind of hole copper specification is required, according to the needs of the product, is ultimately specified by the customer.

PCB hole copper thickness standard and finished copper thickness composition

The following is a general flow chart of conventional PCB:

PCB hole copper thickness standard and finished copper thickness composition

PCB hole copper thickness standard and finished copper thickness composition

We can clearly see from the two figure, our PCB finished copper thickness is by PCB base copper thickness and thickness plate electric and electric, in the end, that is finished copper thickness is greater than the copper base PCB, and we are all the PCB hole copper thickness, are completed in the two processes of electroplating, that is, the thickness of the whole plate hole plating copper electroplating copper thickness and graphics.

The finished copper thickness of PCB is composed of the base copper thickness of PCB plus the final thickness of board electricity and graph electricity, that is to say, the finished copper thickness is greater than the base copper of PCB. The copper thickness of all the holes of our PCB is completed by electroplating in two processes, that is, the copper thickness of the plated holes of the whole board and the copper thickness of the electroplated graphics.

Conventional finished products 1OZ finished copper thickness, hole copper according to IPC level 2 standard, usually a copper (full plate plating) thickness of 5-7um, two copper (graphic plating) thickness of 13-15um, so the hole copper thickness between 18-22um, plus etching and other reasons caused by the loss, the final hole copper is about 20UM.

Standard requirements for copper thickness in hole (IPC-6012B, GJB 362A-96, QJ3103-99)

PCB hole copper thickness standard and finished copper thickness composition

Through hole electroplating is a very important link in PCB manufacturing process. In order to realize the electrical connection of different levels of conductive metal, copper with good electrical conductivity needs to be plated on the hole wall of the through hole. With the increasingly fierce competition of terminal products, it is bound to put forward higher requirements on the reliability of PCB products, and the thickness of through-hole electroplating layer has become one of the items to measure the reliability of PCB. An important factor affecting the copper thickness of PCB hole is the deep plating ability of PCB plating.

An important index to evaluate the effect of PCB plating through hole is the uniformity of copper coating thickness in the hole. In the PCB industry, deep plating capacity is defined as the ratio of the copper coating thickness at the center of the hole to the copper coating thickness at the mouth of the hole.

In order to better describe the ability of deep plating, the thickness aperture ratio, that is, the thickness diameter ratio, is often used.

PCB board is not too thick but the aperture is large, the electric potential distribution in the electroplating process is relatively uniform, the ion diffusion in the hole is relatively good, the electroplating solution deep plating capacity value is often relatively large; On the contrary, when the ratio of thickness to diameter is higher, the hole wall will show the phenomenon of “dog bone”, (the phenomenon of thick copper at the mouth and thin copper at the center of the hole), the deep plating capacity of the bath is poor.

High depth plating capacity has the following advantages:

1. Improve reliability

The uniformity of the thickness of the electroplated copper layer on the hole wall is improved, which provides a better guarantee for the cold and hot impact of PCB in the subsequent surface mounting and the use of terminal products, so as to avoid the failure in the early stage, prolong the service life of products and improve the high reliability of products.

2. Improve production efficiency

Electroplating process is generally the “bottleneck” process in the manufacturing process, the improvement of deep plating capacity can shorten the plating time, improve productivity and efficiency.

3. Reduce manufacturing costs

PCB factories generally believe that if the deep plating capacity is increased by 10%, the material cost can be reduced by at least 10%. The direct benefit of this one item is only one million yuan/year, not to mention a series of indirect benefits after improving product quality.