Eurocircuits Printed circuits blog

Gold plating over edge connectors

Eurocircuits offer two types of gold finish: Electroless Nickel Immersion Gold (ENIG) as a surface finish for the whole PCB, and hard plated gold over plated nickel for edge-connector fingers. Electroless gold gives excellent solderability, but the chemical deposition process means that it is too soft and too thin to withstand repeated abrasion. Electroplated gold is thicker and harder making it ideal for edge-connector contacts for PCBs which will be repeatedly plugged in and removed.

To produce your board we use your design data in Gerber or EAGLE format and first perform the necessary front end actions as described in our white paper: "What do PCB fabricators do with your data before they make your PCBs?".

When this is done and your board is ready for production, we save your board’s production data in your account.  This data we call the job’s "single image" data.  “Single image” means the data we load onto our order-pooling production multi-panels, so it may refer to a single circuit image or to a delivery panel if this is what you have ordered. This is the data that is visualized in the PCB image.  You can download the full set from within your customer account.

Soldermask on via holes

There are 3 ways our customers prepare their layouts with respect to covering via-holes with soldermask:

• Vias open (not covered by soldermask) on both sides of the PCB
• 
• Vias closed (covered with soldermask) on both sides of the PCB
• 
• Vias open from one side and covered from the other side of the PCB
• 

As necessary background information we need to briefly introduce you into the technology of applying soldermask to the boards.

On April 25, ACB organized their technology seminar….Eyes on the future, feet on the ground…

ACB, known in Europe as leading manufacturer of High Technology & Quick Turnaround Printed Circuit Boards, organized its first technology seminar.

The brand new CEO, Gilles Rigon, opened he seminar with explaining all about the ACB philosophy.   “S” for simple and easy solutions where possible, “S” for souple and flexible processes and “S” for Solid and reliable processes and how they balance their “eyes on the future” with their “feet on the ground” approach.  In fact, the importance of this balance would return in many lectures coming.

Large boards and pooling – new guidelines

Over the last 12 months we have received an increasing number of boards in our pooling services at the maximum size allowed 425 x 425 mm.  These are not genuine single circuits but panels made up of many smaller circuits.  To get around our specified maximum panel size 350 x 250 mm, the individual circuits on these oversize panels are not profiled out.  In that way the users can describe the panel as a single circuit, though we know, of course, that they will subsequently cut out the individual circuits.

This practice raises two serious issues.

Eurocircuits'role in the project sets a new competitive standard

Making efficient pooling panels belongs to the core business of Eurocircuits. It is a necessity to ensure cost-effective production of prototypes or small batches. 
Eurocircuits started as a trader of printed circuit boards in 1991. Soon after, in 1993 we got involved in production. It has been our aim from the start to use pooling techniques for a number of reasons :

• Save cost by increasing production efficiency
• Save the environment by reducing waste

The idea of making pooling panels was not new in 1993. On the Benelux market a dutch company was already successfully offering single sided boards in pooling since the eighties of the last century. For double sided boards however it was not that common yet.

When we introduced combination panels for double sided boards in our own production in Hungary there was a lot of resistance from the operators and from the production management. They saw the complexity of their job increase, and technological challenges had to be taken care of.

Now, almost 20 years later, most technology issues have been taken care of, except for one major area, the galvanic copper plating.

For this galvanic process, the design of the PCB plays a vital role in the outcome of the process. In pooling panels there is even an influence of the design of one board on the copper deposition on surrounding designs. That means that we have to be very careful how to build our panel layouts.

The restrictions in panel configuration create limitations that affect the efficiency in our production. As a producer you can look at this problem in two ways:

• Focus on efficiency and accept uneven copper distribution. Also accept that the quality of the PCB's produced for one customer can be influenced by the design of another pcb on the same pooling panel.
• Focus on quality - stick to an even distribution and minimum copper plating thickness all over the panel. Accept that part of the panel surface gets lost because of extra copper areas and spacing introduced to balance out the galvanic layer. Also accept that not all jobs can be pooled with acceptable plating results.

Eurocircuits decided not to take any plating quality risks. We accepted the restrictions dictated by the plating process for a long time.The Elsyca Intellitool matrix copper plating is going to remove these restrictions.

What is Bow and Twist?

According to the IPC-A-600 standard bow and twist (flatness of the board) is :

“Flatness of printed boards is determined by two characteristics of the product; these are known as bow and twist. The bow condition is characterized by a roughly cylindrical or spherical curvature of the board while its four corners are in the same plane. Twist is the board deformation parallel to the diagonal of the board such that one corner is not in the same plane to the other three. Circular or elliptical boards must be evaluated at the highest point of vertical displacement. Bow and twist may be influenced by the board design as different circuit configurations or layer construction of multilayer printed boards can result in different stress or stress relief conditions. Board thickness and material properties are other factors that influence the resulting board flatness.”

Why is the flatness of a printed circuit board important?

• During the production of the board the flatness of the panels is important for handling and for positioning the panels on the machines
• During the assembly process the flatness of the panels is important for correct solder paste deposition and component mounting
• Flatness is an aspect of the visual quality appearance of the boards.

What are the acceptability criteria for bow and twist?

• For all boards the bow and twist should be 1.5 % or less
• For boards using SMD components ( the majority of the boards) the bow and twist shall be 0.75% or less.

How to measure the bow and twist?

The IPC-TM-650 test methods manual describes the method to calculate bow and twist percentages

What can the PCB designer do to avoid bow and twist?

Surface Finishes on printed circuit boards

Then finally, you have finished your design and the moment has come to order the PCB.  You have considered all the important aspects. The DRC check is done and you are relieved: no errors remaining.

The online calculator shows you the default pooling options and offers you the possibility to adjust some of them to your specific need.  En there you bump onto the Surface Finish.  What is Surface Finish and how to make the right choice?

Since all finishes have advantages and disadvantages, it is important to stand still by their application and to check how your boards will be treated during assembly.   The different finishes we offer are Lead-free HAL, Electroless Nickel/Immersion Gold (known as ENIG) and Immersion Silver (ImAg).  All of these are Lead-free and can be used for a RoHS design but also in a SnPb assembly.  Edge connectors can be covered with hard Gold (electroplated Ni/Au).

PIP (Pin in Paste) technology for soldering trough hole components

PIP is a technology for assembling through hole components using a conventional reflow soldering process. The process is also known as THTR (Trough Hole Technology Reflow).

Most PCB's that contain SMD components usually also contain some through hole components, such as connectors, switches, capacitors and so on . The principle of PIP is that through hole components are placed into PTH holes with SMT solder past and then reflow soldered with the other SMT components together.

We judge this can be a technology of interest for electronics developers that decide to assemble their prototypes themselves.

The next figure shows the process sequence we advise :

Important parameters for this process are hole and pin sizes, boards thickness, thickness and opening of the stencil , used paste printing technique and used paste.

It is obvious that only components that can withstand the reflow soldering temperatures can be soldered this way.

Most datasheets for PIP connectors also contain useful infomation such as the recommended stencil design.

Some hints based on our experience to give you the best results: