Defect of The Month – PCB Delamination

Hello, my name is Bob Willis and welcome to Defect of the Month. 

Now this month, I wanted to talk about PCB delamination, this is where we have a multilayer printed board or a flexible circuit that shows separation between different layers of the construction. The board has separated away from each other often with visible bubbles/blisters

 

Our images above show areas of delamination, bubbles or via lifting

Now this would normally occur during the soldering operation, reflow soldering or possibly a rework operation. It’s unlikely that you would see this on wave or selective soldering, but it’s perfectly possible for it to happen. If there is any poor bonding of the board layers or there is a high level of moisture in the board, these are reasons why you could see separation. 

If you’ve got moisture inside the printed circuit board and you’re heating it up it expands at reflow temperatures, this may be sufficient to generate sufficient energy to separate surfaces within a board. Now my personal experience is, wherever possible try and QC the printed circuit board suppliers you are using to minimise the need for baking particularly if we’re talking about four layer multi-layers. Boards are fairly inexpensive, it’s the components that we add to the circuit which increased the value of the printed circuit board plus the time on assembly. Time looking at the supplier and the quality of manufacture is one of the key issues to consider. Visit the supplier, test the product, understand the fabrication process and the materials he is using

Sometimes if you’re in very high volume, losing a few boards is not necessarily a reason to justify going through a baking operation. Specify better packing materials may be an alternative to reduce moisture during shipment to your site.  We must try and make sure we have a quality board that is well laminated and there are no internal issues to start off with. The reason being that the baking operation would in terms of cost and aggravation of handling really negate the value of the baking operation. 

Now, if we have a delamination issue, then the first thing to try two understand why and where separation has occurred it may not be visible. Now we can do practical things like micro sections or event high end x-ray investigation can spot potential problems.

Our microsection images above show internal delamination, lifting and separation. X-ray can also show through via damage after soldering without destroying the board. This could then be used to pin point the best location for sectioning an intermittent board

I favour taking a printed circuit board and separating the different layers mechanically, literally by just cutting out the bubble that can form in the board and finding out if there has been good lamination to start off with. When you do this, you can quite often show that lamination, basically the bonding of the epoxy to the copper surface is an issue. This or separation of the oxide treatment to promote adhesion hasn’t been done correctly, or some other factor has affected it. This is fairly simple analysis to determine the potential root cause of the failure. The other benefit to simple mechanical separation, if done correctly the separated surface can be reexamined. These cannot be examined if you have sectioned the board.

 

Images above show simple mechanical examination of delamination with a good understanding of the fabrication process it is a simple, inexpensive and practical shop floor test. The author has conducted this on many production lines around the world

Of course, I totally agree, it’s moisture that is the driving force. But if you have a poor quality board to start with a minimum amount of moisture can also cause separation with higher process temperatures. In rework and repair without prior baking of the board assembly remember, as I said earlier that the board assembly time and the components are probably the main value that you’re adding to the basic board. So it’s good practise to buy good quality boards and it’s not because we’re just concerned about delamination of the printed circuit board. It’s the other components also. 

 

Images show delamination of Area Array Packages which in many cases are just small PCBs

If we’ve got multilayer boards plus a combination of area array packages, moisture content in the components could also see significantly damage and consequently suffer intermittent failures. So we must think about why we do certain things. If you’ve got delamination of a board, be it a flexible flexi rigid or a traditional multilayer board. Look for why they’re separated, understanding that it may be driven by moisture, always understand the root cause of the problem.

We have many other Defect of The Month videos and our online articles which we hope will help you solve your process and product failures. We have also listed a small selection of over 100plus videos created over many years. 

If you would like to download any of our Process Defect Guides or my three soldering books FREE just drop me an email bob@bobwillis.co.uk