Before you do anything regarding planning your new circuit board layout, one thing you will have to do is designing the stackup as well as selecting your board’s material system. The circuit board laminate materials may seem simple. You believe it works like choosing your desired material and vendor, putting them in your stackup, then sending it to the fabricator.

The truth is that not every fabricator out there stock or support all the laminate materials possible. However there are some materials, which are compatible with themselves in the different stackups. Now, in what ways can you spot the resin system and materials that will be interchanged in the PCB stackup?

Enter the IPC standard IPC-4101 slash sheets. This standard helps in specifying the different requirements for the materials of the PCB laminate which helps in ensuring the compatibility and interchangeability in the PCB stackup. Though it is not required to read any slash sheets during the selection of materials, having understanding of what’s present in the slash sheet may assist you in determining the alternate materials when the desired laminates are not supported or available by the manufacturer.

The Origin of the IPC 4101 Slash Sheet

Under IPC standards, the IPC 4101 slash sheets can be described as addenda which stats the requirements for the different laminates for the PCB stackups. The IPC 4101 standard utilized most of the initial languages from the MIL-S-13949 standard.

The slash sheets requirements for IPC 4101 persist till today and the laminate materials would list these slash sheets onto which the materials conform. If you check the website of a laminate manufacturer, or you check the datasheets of their laminate, you will most likely see something like “/24” or”/121” for some specific laminates. This refers to the IPC 4101 24 or IPC 4101/121 slash sheets respectively. Others include IPC 4101 126, IPC 4101 21, IPC 4101 26, and IPC 4101 41.

What Can You Find in a Slash Sheet?

The slash sheet features two data sets on a specific material system. These are the material/primary structural properties, as well as some results for testing as determined using the IRC testing standard. In addition, any slash sheet begins with structural and material specifications for that specific laminate.

All manufacturers have their material names which aid in communicating the specific laminates onto the public and the customers. However, there will be a relationship between the laminates and the IPC 4101 standard. Below are some of the information you will find in slash sheets.

• Type of reinforcement which is usually fiberglass
• All flame retardants and filler materials available in the laminates
• Tg or glass transition temperature
• Resin material systems (which is usually an epoxy mix)

What is IPC 4101?

IPC 401 can be described as a specification for the base materials designed for multilayer and rigid printed circuit boards. It was released in December 1997. This came as a replacement for the MIL-S-13949 standard. Moreover, it had most of the same wording seen in the military standard.

Furthermore, its format appendix was maintained to a standard specifying the fiber and resin system of several PCB laminates, in addition to the properties and testing parameters. At first, 41 (forty-one) slash sheets were available; however, as the industry decided to work with “Green” and “Lead Free” processes, these slash sheets increased in number to sixty six (66).

With all these slash sheets, having a good understanding of what they are would offer great benefits to the choosing of the right properties of the laminate to suit your PCB design.

Laminate Specification of IPC 4101

All slash sheets start with a laminate specification. It involves the type of reinforcement, the resin system, the mechanism of the flame retardant, glass transition, and fillers. This type of reinforcement seems to be fiberglass (woven E-glass).

However, it could also be exotic fiberglass and cellulose paper types like aramid and unidirectional fiber. This serves as the laminate’s structure component. Also, resin systems could be a combination of different types of epoxies to meet the laminate type’s requirements. The main epoxy would be listed, after this, the secondary follows, and another secondary may even follow.

Utilizing Epoxy Resins

 Some exotic resin systems like Polyphenylene and polyimide exist. This resin system binds the layers of the structure together. This flame retardant is usually RoHS compliant bromine or bromine, and phosphorus as another option as well. Fillers could be inorganic or not applicable, with just a few types of laminate making use of kaolin fillers. These fillers help in reducing resin shrinkage, therefore, reducing the formation of cracks in the filled areas.

Temperature of Glass Transition (Tg)

The temperature of glass transition describes the range of temperature whereby the resin’s molecules transits from its brittle and rigid state into its pliable and flexible state. The Tg was added to the area of specification because many designers decided to base their choice of laminate for compliance of RoHS on the Tg material. Asides from Several other factors which have to be considered during the selection of laminates.

Other Characteristics That You Must Be Aware of

The remaining slash sheet must list the requirements of the laminate for the material characteristics, which are tested for every IPC-TM-650 test method. Some of these features are highlighted below.

• The peel strength helps in determining the metal cladding bond whenever it is tested after thermal stress, as well as after exposure to some processing chemicals
• Absorption of moisture or moisture absorption helps in determining the absorption rate for that epoxy composite utilized in the structure of the laminate. Also, all the resin systems help in absorbing some moisture whenever it is exposed to a high humidity environment.
• Surface and volume resistivity determines the surface and cross-sectional electrical resistance of a dielectric material when under some humid conditions.
• Dielectric breakdown measures the ability of the insulator to withstand the high voltages stress that is placed across.
• Loss Tangent can be described as a measure of the amount of electromagnetic field that travels through the dielectric is lost or absorbed in the dielectric
• Also, you can determine flexural strength with laminates having a thickness of 0.51 mm or greater through the application of a load to a size as well as shaped specimen.
• Thermal stress helps in determining the metallic clad or unclad laminates’ thermal integrity making use of short-term solder exposure.
• Arc resistance measures the required time to make the insulating surface to be conductive when under low current and high voltage arc.

IPC 4101 vs IPC 4103: What’s the Difference?

When searching for slash sheets from your laminate manufacturer, you may see both IPC 4101 and IPC 4103 standards. This IPC 4101 standard deals with the standard laminates as well as prepreg materials, thereby encompassing the materials of epoxy resin with fiberglass.

Though the standard initially specified a total of forty-one slash sheets, this number has increased to over sixty slash sheets. This is made possible by RoHS regulations as well as focus on the lead-free environmentally-friendly materials. This IPC-4102 also extends the slash sheets to the copper-unclad as and clad plastic laminate materials as well as bondply materials utilized in high frequency and high speed PCBs.

Calculate and Plan Your Stackup Early

Most, if not everyone, have a manufacturer that they prefer to use. With time, when you continue to order from one manufacturer, you will be very familiar with the materials as well as the stackups that they support.

Normally, this is listed by the laminate vendor number and name, instead of making use of slash sheet numbers. Moreover, there are fab houses that need you to specify the stackup you desire through a slash sheet. T5his is why it is important that this information is gotten from your own laminate manufacturer whenever you are submitting an order.

Preferred Circuit Board Stackups

Majority of manufacturers have stackups that they prefer, which are utilized for some layer counts and they are sure of passing through their process of fabrication. These stackups they prefer will feature some specific material systems. Make sure you work closely with the fabricator ensuring that your ideal stackup will be supported throughout the entire process

Where You Can Find Stackup Data

There are several fabrication houses that will place this online, while others will decide to email it to you. Whatever the case is, try to ask early. Failure to do this could lead to a very complex redesign when the stackup needs to be modified in the completed PCB layout, most especially whenever you are working with an impedance controlled board.

Furthermore, ensure you check your data sheets from the two materials to ensure their compatibility. You may even go ahead and order test samples, just to check the Thermomechanical and impedance properties.

Conclusion

In summary, IPC 4101 can be described as an industry guideline for the printed circuit boards’ base laminates. Having a good understanding regarding the structure and content will lead the designers to select the laminate which best offers support to the final requirements of the product.