Fresh PCB Concepts: Does the Assembly Process Damage a PCB? (Part 2—Time to Delamination)

David_Duross_NCAB.jpg

In part 1 of this series, I commented upon the effect that the assembly process has upon a printed circuit board. The assembly temperatures applied do, in fact, burn away the epoxy of the FR-4 composite material. The higher the temperature, the faster the rate of burn. I touched upon the relationship between the glass transition temperature (Tg), decomposition temperature (Td), and the maximum continuous operating temperature (MOT). There is another gauge that can be used to help a designer or contract manufacturer understand this point and that is the time to delamination test. These are referred to as either the T260 or T288 tests.

What is the T260/T288 Time to Delamination?
This is a test defined by the IPC under IPC-TM-650 Test Method 2.4.24.1. A test sample is incrementally raised in temperature 10°C/min to 260°C (or 288°C) and then dwells at 260°C (or 288°C). When an event occurs such as delamination, cracking, moisture release, stress relaxation, decomposition, or a sudden movement, a sensor detects the change. The time in minutes from the start of the dwell time to the event at 260°C (or 288°C) is the time to delamination.

How Does This Value Relate to Anything in the Assembly Process?
The T260/T288 test values are a gauge of how durable the FR-4 shall be when exposed to heat for long periods of time. FR-4 is a NEMA grade designation for glass-reinforced epoxy laminate material that is flame-resistant. It is a general designation that applies to many different materials with different performance levels. The performance levels shall vary between different laminate manufacturers and material grades they manufacture. No two grades of FR-4 from different laminate manufacturers are exactly alike. They all meet the minimum NEMA requirements to be labeled as FR-4. Some grades of FR-4 are superior to others.

T260/T288 values are listed on a laminate manufacturer’s material datasheet. The higher the reported value, the better the performance of the FR-4 when exposed to soldering temperatures. There is one important point to remember: The reported values are generated from pristine and uniform test samples. The values are optimal and do not take the PCB design into consideration.

As soon as you start building a printed circuit board you introduce variables. For example, when you form plated through-holes you have to drill holes. When you drill a hole there shall be some fracturing of the laminate at the hole wall. The fracturing is an imperfection but it’s the result of the printed circuit board manufacturing process. Fracturing is a potential weakness and ultimately a source from where delamination may propagate from. The tested value on the laminate manufacturer's datasheet does not reflect the printed circuit board overall performance. It is an indication for the potential of the FR-4 material, not the manufactured printed circuit board.

The higher the T260/T288 values the better the PCB shall perform when exposed to heat. For conventional eutectic soldering consisting of tin-lead the T260/T288 results are not a critical piece of information to have. For lead-free soldering temperatures it’s an important piece of information to consider. For example, compare two grades of FR-4 from the same laminate manufacturer:

Epoxy System #1:            
Dicey cured Tg 170°C (Conventional FR-4)
T260 = 10 minutes
T288 = 2 minutes

Epoxy System #2:
Phenolic cured Tg 170°C (Lead-Free Assembly-Compliant FR-4)
T260 > 60 minutes
T288 = 30 minutes

As you can see, the difference between the two results is dramatic. The T260 test is essentially close to lead-free assembly temperatures. Using a dicey cured epoxy system for lead-free soldering applications is not advisable. The closer you are to lead-free soldering temperatures the faster the epoxy burns away. The phenolic cured epoxy system offers much more in regards to thermal resistance and durability. The phenolic cured epoxy still burns away but at a much slower rate. You'll notice that the T260 result for the phenolic cured laminate is greater than 60 minutes. This only means that the test time exceeded 60 minutes without a failure and the laminate manufacturer stopped the test.

David Duross is an engineering director for NCAB Group USA.

Back

2021

Fresh PCB Concepts: Does the Assembly Process Damage a PCB? (Part 2—Time to Delamination)

08-12-2021

In part 1 of this series published back in April, I commented upon the effect the assembly process has upon a printed circuit board. There is another gauge that can be used to help a designer or contract manufacturer understand this point and that is the time to delamination test. These are referred to as either the T260 or T288 tests.

View Story

Fresh PCB Concepts: Auditing a Factory—When Everyone Wins in the PCB Supply Chain

07-25-2021

One of the most important activities when it comes to maintaining the best quality of PCBs is to constantly be evaluating partner factories. An important tool for securing this is auditing those factories on a consistent basis. When the factory develops and the bar gets pushed a little higher each time, we’re in a situation where we all benefit.

View Story

Fresh PCB Concepts: HDI Microvia Features in Illustrations

06-17-2021

Ruben Contreras explains microvias and discusses aspect ratios with microvias. This is important to know when designing an HDI PCB because the different types vary in complexity. And the more complex, the more this affects the cost.

View Story

Fresh PCB Concepts: Does the Assembly Process Damage a PCB? (Part 1—Soldering)

04-14-2021

Every time a printed circuit board is exposed to soldering temperatures it is damaged. This is the case not only for lead-free soldering applications but also for eutectic soldering consisting of tin-lead.

View Story

Fresh PCB Concepts: Mitigating the Increasing Prices of PCBs

03-18-2021

By now, you might have noticed that the cost of PCBs is increasing. What’s worse is that there are also supply chain issues causing additional delays on PCBs. You can’t redesign every board in order to reduce cost. Instead, try these tips to help you reduce manufacturing costs.

View Story

Fresh PCB Concepts: UL Certification for the Safety of PCBs

02-18-2021

Security is essential in the electronics industry. It is vital that users can rely on the finished products when considering factors such as fire and electrical safety, which means that both the PCB and the materials they contain must measure up to the highest standards. To ensure that the boards do conform, it has become common practice to UL certify the constituent materials or the PCB itself. In this column I am going to discuss UL certification, what’s involved and why you need it.

View Story

Fresh PCB Concepts: RF PCB Designs–Challenges, Solutions and Tips

01-14-2021

Today, RF circuitry is crammed into a large variety of commercial products. Most of these are handheld wireless devices for medical, industrial, and communications applications. There are also applications in a variety of fields that are migrating from desktop models to become portable communications units.

View Story
Back

2020

Fresh PCB Concepts: How 5G is Influencing PCB Technology Trends

12-17-2020

We have all heard about the Internet of Things (IoT) and artificial intelligence (AI). In combination with the increased data transfer rates available through 5G, they can open up a whole new level of connectivity and communication between devices and things.

View Story

Fresh PCB Concepts: Finding and Qualifying a Long-Term Partner

11-05-2020

Finding the right factories is not an easy task. Anyone can take customers’ files and send them to whichever factory is available. But what guarantees does the customer have that the factory used is reliable in producing the design? Ruben Contreras details how to find and qualify a long-term partner.

View Story

Fresh PCB Concepts: 4 Characteristics to Consider When Selecting PCB Base Materials

10-08-2020

Selecting the correct material is critical if you want your circuit board to survive the assembly process or come out of the assembly process in good condition. Jeffrey Beauchamp explains the four main characteristics from the IPC-4101 material specification that are critical in finding the performance of your base material.

View Story

Fresh PCB Concepts: Advantages of Application-Engineered PCBs

09-17-2020

When working with your PCB supplier, do you have a dedicated engineering resource to help with the design of your PCB before fabrication? How about a resource that has experience and knowledge about the different applications for PCBs? Jeffrey Beauchamp explains how this is one of the most important and valuable factors when producing high-reliability PCBs, as well as what—or who—this resource could be.

View Story

Fresh PCB Concepts: How Do You Calculate Finished Copper?

08-13-2020

How do you calculate finished copper on a PCB? This may sound simple, but Ruben Contreras has seen copper thickness called out either on the drawing or the specification, which can lead to additional EQs and, in some cases, additional costs. In this column, he explains the unintentional results that can come from misunderstanding what was requested.

View Story

Fresh PCB Concepts: Pros and Cons of the 6 Most Common Surface Finishes

07-23-2020

There are only two different types of surface finishes for PCBs: organic and metal. Harry Kennedy describes the pros and cons of the six most common finishes on the market.

View Story

Fresh PCB Concepts: 7 Options for Via Treatment

06-18-2020

In some cases, it's acceptable to have via holes that are completely exposed in a PCB design. But there are many others where the hole should either be covered and/or tented, or in most cases, plugged. Jeffrey Beauchamp shares seven different via hole protection types based on IPC-4761.

View Story

Fresh PCB Concepts: Why Design and Produce PCBs Beyond Industry Specification?

05-07-2020

While questions may be an annoyance, especially when you finally have a board designed and are ready to have it built for a product, Ruben Contreras explains the importance of asking these questions and requiring specifications.

View Story

Fresh PCB Concepts: What You Should Know About Your Board’s Solder Mask

04-09-2020

It’s a weird time we’re all in, and for most designers, work has slowed down or even stopped. While work might have slowed, now is a good time to review some of your past PCB projects to see if you can improve functionality and reduce field failures. Harry Kennedy explains how one of the simplest ways to do that is to start from the top: solder mask.

View Story

Fresh PCB Concepts: The Benefits of Being a PCB Producer Without Owning Any Factories

03-19-2020

With NCAB's infrastructure and factory management team based in China, many customers ask why they don’t own any factories. Jeffrey Beauchamp explains how it's part of the company's long-term strategy and an advantage to our customers that they don’t own any factories. Instead, they “own” what is most important: the relationship with the factory.

View Story
Back

2019

Fresh PCB Concepts: Designing a PCB for Telecom Applications

12-12-2019

Jeff Beauchamp and Harry Kennedy discuss PCBs for telecommunication applications, including key factors to consider, such as design and material considerations. They also recommend involving your PCB supplier at the time of design to help ensure manufacturability at the lowest possible cost.

View Story

Fresh PCB Concepts: The Current Material Situation

11-11-2019

We have all heard about the component crisis in the circuit board industry, and maybe you heard about the CCL shortage, but how many are aware of the bare board material shortage? Ruben Contreras explains the current material situation and tips to address this issue.

View Story

Fresh PCB Concepts: Getting It Right From the Start

10-23-2019

When faced with critical time-to-market situations, it is all too easy to say, “It doesn’t matter because this is just the prototype; we can fix this later.” However, if the design is perfected from the beginning, cost savings can be applied, and manufacturability can be ensured. Perhaps most importantly, the design can be adapted with reliability in mind, leaving a seamless transition from prototype to production. How do we get it right from the start?

View Story

Fresh PCB Concepts: Why Material Selection Matters

10-02-2019

When you’re designing a PCB, it’s standard to call out FR-4 material, but you could be holding yourself back or even exposing your board to risk by not knowing more about PCB materials. Let’s take a small look into why. What Is FR-4, exactly? Harry Kennedy of NCAB explains.

View Story

Fresh PCB Concepts: Qualities of Medically Applied PCBs

08-26-2019

In this inaugural column from NCAB Group, Alifiya Arastu discusses details of PCBs used in medical applications, highlighting some of the differences in terms of demands and how the design must be handled.

View Story
Copyright © 2021 I-Connect007. All rights reserved.