Evaluation of reliability of semiconductor package mounting ~ Daisy Chain Sample to Identify Broken Location ~

Hello, everyone. I’m Matsumae for structural engineering section.

I am involved in the development of mounting technology and mounting reliability technology for semiconductor packages. The main target is the BGA type packages.

In this article, I will talk about daisy-chain samples that are used to evaluate the reliability of semiconductor package mounting.

Broadly speaking, BGA-type semiconductor packages are consist of

  • Si chip, the heart of the device,
  • Package substrate as a base, and
  • Terminals (solder balls) to connect to a PCB for mounting.

There is also a type where the package is molded with resin and a type where a heat sink is attached to the Si chip. (Figure 1)

 

Figure1. Example of BGA-type semiconductor packages

 

Semiconductor packages are mounted on PCBs of our customers (manufacturers of automotive and mobile devices, etc.). (Figure 2) Therefore, it is very important to ensure a secure connection between the semiconductor package and the PCB at the customers’ manufacturing process (mountability) and that the connection is maintained during the use as a final product (mounting reliability).

 

Figure 2. Semiconductor packages mounted on a PCB

 

Temperature cycling and mechanical strength tests are used to evaluate mounting reliability. At that time, a sample with a wiring design called a daisy chain is used for evaluation. In electronics, the term “daisy chain” refers to the linking of multiple devices together to form a series of chains. A daisy-chain sample used to evaluate the reliability of semiconductor package mounting is designed to form a series circuit between the package substrate and the mounting PCB to be evaluated and the terminals (solder balls) that connect them.

 

Figure 3. Wiring structure of daisy chain

 

The test is performed with the IN and OUT sides connected to the resistance recorder and continuously monitored. (Figure 4) If the terminals are broken during the test, the resistance changes (usually open = infinity), so you can find out when the connection is no longer maintained.

 

Figure 4. Continuous monitoring of test

 

Usually, as shown in Fig. 5, it is prepared not only IN and OUT, but also tapped out wires from the middle of the package wiring as well as test pads for them on the substrate for evaluations. By checking the continuity between the test pads with a tester after the test, you can determine which terminal has broken.

 

Figure 5. Continuous monitoring of test conditions

 

The daisy chain sample is for evaluation purposes only. So, it is necessary to make a sample with dedicated design which is separate from the actual product. However, it is a very effective method to properly evaluate the mounting reliability.

However, in making this daisy-chain sample, it is not possible to check all pins in a package with large number of pins in most cases. So, you have to carry out a wiring of a daisy chain after determining which pins to focus on in advance by a simulation.
(Incidentally, we also offer a conductor resistance monitoring system that monitors continuity during reliability tests of this daisy chain in real time.)

This time, I explained about daisy chain samples used for evaluation of reliability of semiconductor package mounting, but WTI is able to respond to various consultations of customers based on the experience and knowledge obtained in the past design and evaluation.

Examples of customer consultations;

  • We want to create a PCB for evaluating the reliability of a semiconductor package.
  • We want to confirm the mounting reliability of the semiconductor package by simulation.
  • We would like to consider a system that can evaluate a large number of packages simultaneously, which is not available on the market.

This is a service we would like to offer to customers who are having trouble with these kinds of cases.

We also offer other services besides the above, so please feel free to contact us for more information.

 

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