Specifying PCB Laminates to Your Performance Needs

Manufacturing That Eliminates Risk & Improves Reliability

Specifying PCB Laminates to Your Performance Needs

02.24.17

Manufacturing That Eliminates Risk & Improves Reliability2

Agenda

Overview of FR4 Materials

High Frequency PCB Applications

Properties of Commonly Used High Frequency Materials

Specific Examples


Start With FR4 & IPC-4101C

The majority of printed circuit boards can be built using generic FR 4 laminates, without significant impact upon the PCB’s performance.

Specifying your laminate in accordance with the appropriate “slash number” from IPC4101C gives your fabricator discretion to use a qualified product that they stock as standard, thereby saving you money and time.

If your PCB does not have critical thermal or electrical requirements, then we recommend that you do call out your material per IPC4101C.

Blog Post - Understanding An IPC 4101 Slash Sheet

http://blog.epectec.com/understanding-an-ipc-4101-slash-sheet


Start With FR4 And IPC-4101C

The majority of printed circuit boards can be built using generic FR 4 laminates, without significant impact upon the PCB’s performance.

Specifying your laminate in accordance with the appropriate “slash number” from IPC4101C gives your fabricator discretion to use a qualified product that they stock as standard, thereby saving you money and time.

If your PCB does not have critical thermal or electrical requirements, then we recommend that you do call out your material per IPC4101C.


Material Performance Beyond The IPC Minimums

Some FR4 designs have special requirements more stringent than the 4101C minimums. For example, even within a single IPC sub-type, the Tg and Td may vary widely (provided they meet the minimums) as can the Dk and Df.

What to do if your relativelycomplex PCB needs specificthermal or electrical performancecharacteristics which go beyondthe generic properties called outin the IPC specification?


List The Critical Properties

In these cases, you can still use an IPC-4101C callout, but add the special requirements to your notes so they will not be overlooked.

The fabricator will select andsuggest a laminate systemwhich will meet all of therequirements, including thosewhich may exceed the minimumvalues used in the IPC spec.


High Performance FR4 Products

► When signal integrity is critical, there are specialty materials that offer excellent performance, but still fall into the FR4 epoxy / glass category.

► These transitional products, such as Nelco 4000-13EP and Isola I-Speed, also offer outstanding thermal and mechanical performance, and are worth considering when they match the requirements of your design.










The Next Step: High Speed / High Frequency Materials

For applications which exceed the limitations of FR4 materials, it is necessary to consider stepping up to High Speed / High Frequency material types.

These materials typically have extremely lowDk and Df characteristics.

Their properties are defined in an entirely separatespecification, IPC-4103A.


Material Callout IAW IPC-4103A

IPC-4103A goes into more detail about the signal speed and loss characteristics of the laminate, which are extremely critical in high frequency designs such as antennas, radar, and RFID products.

If you do not specify a particular manufacturer’s product, you may use Table 1-1 and 1-2 to specify the material in accordance with the specification.


Material Callout IAW IPC-4103A

IPC-4103A goes into more detail about the signal speed and loss characteristics of the laminate, which are extremely critical in high frequency designs such as antennas, radar, and RFID products.

If you do not specify a particular manufacturer’s product, you may use Table 1-1 and 1-2 to specify the material in accordance with the specification.


Which Materials To Choose While there are specialty materials available for a wide variety of high

frequency applications, some are more readily available than others.

Commonly requested types are the Rogers 3000 and 4000 series, Taconic RF35 and RF45, and Arlon Cuclad, but others are available.

Your fabricator may not be UL certified for a particular product. UL certification is an involved and costly process, so while a fabricator may be willing to build with a certain material, they may not beable to add their UL marking.

If you require UL compliance, be sure tostate that in your documentation.

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Composition Of Different Sub-Types

Many high frequency materials, such as PTFE (Teflon) can be difficult for fabricators to work with.

Because of this, material manufacturers have developed products which can be processed much like FR4 types.

Some (the Rogers 4000 series, for example) utilize hydrocarbon ceramic with glass reinforcement. Others, such as the Rogers 3000 series, combine PTFE with ceramic fillers.


Composition Of Different Sub-Types

Many high frequency materials, such as PTFE (Teflon) can be difficult for fabricators to work with.

Because of this, material manufacturers have developed products which can be processed much like FR4 types.

Some (the Rogers 4000 series, for example) utilize hydrocarbon ceramic with glass reinforcement. Others, such as the Rogers 3000 series, combine PTFE with ceramic fillers.


Applications For Different Sub-Types

When selecting materials for your project, the manufacturer’s product data sheets contain a wealth of detailed information.

In addition to explaining the material’s composition and properties, the data sheet will list applications for which the product is suited.

Below are two examples from Rogers. On the left is a ceramic-filled PTFE type, and on the right is a hydrocarbon / ceramic / glass type.


Applications For Different Sub-Types

When selecting materials for your project, the manufacturer’s product data sheets contain a wealth of detailed information.

In addition to explaining the material’s composition and properties, the data sheet will list applications for which the product is suited.

Below are two examples from Rogers. On the left is a ceramic-filled PTFE type, and on the right is a hydrocarbon / ceramic / glass type.


The Effect Of Glass At Microwave Frequencies

In radar sensors used in accident-avoidance or automatic braking sensors, wavelengths are so short that the glass reinforcement can cause small variations in Dk and phase.

Automotive volumes are such that these variations are unacceptable.


An Appropriate Material With No Glass

Rogers 3003 uses no glass. Its physical properties allow it to function correctly in either all-Rogers or FR4 hybrid multilayers for automotive and 5G wireless devices.

Typical Applications– Automotive radar– RF Couplers– Cost Sensitive Aerospace & Defense Applications– GPS Antennas


Simple 2-core Lamination Using High Speed Materials Only

► Here is a stack-up for a 3-layer PCB. It specifies (2) 4350B cores, laminated together with Bond Ply.

► Notice that it is a 3-layer design. The copper is removed from one side of the 2nd core prior to lamination.


High Frequency Material Cost Factors

Some Cost Factors– High frequency laminates cost significantly more than FR4 types.

– The multiplier ranges from approximately 4x to 8x, depending on volume.

– Because of this, most fabricators do not keep a large supply in inventory.

– The lack of inventory means that materialis often bought as-needed. If the order issmall, it may be subject to a minimumorder quantity surcharge.

– Such orders are often subject toexpedited shipping charges.


Processing Costs Associated With High Frequency Laminates

► Incorrect surface prep before lamination can adversely affect adhesion.

► Overly aggressive surface prep can also distort the material.

► Drilling: Ceramic types in particular shorten drill life considerably.

► Hole prep for plating, especially PTFE types, may require different processing which not every fabricator possesses.


Processing Costs Associated With High Frequency Laminates

► Incorrect surface prep before lamination can adversely affect adhesion.

► Overly aggressive surface prep can also distort the material.

► Drilling: Ceramic types in particular shorten drill life considerably.

► Hole prep for plating, especially PTFE types, may require different processing which not every fabricator possesses.


Hybrids: Reducing Cost Where Possible

► Because the material itself is such a large factor in the overall cost structure of the board, consider substituting FR4 materials at non-critical layer positions.

► Certain high speed materials are formulated for compatibility in such “hybrid” stack-ups. It is especially important that the CTE (coefficient of thermal expansion) of the high speed material be closely matched to that of the FR4. Otherwise the unlike materials will expand at different rates under thermal stress.


Hybrids: Reducing Cost Where Possible

► Because the material itself is such a large factor in the overall cost structure of the board, consider substituting FR4 materials at non-critical layer positions.

► Certain high speed materials are formulated for compatibility in such “hybrid” stack-ups. It is especially important that the CTE (coefficient of thermal expansion) of the high speed material be closely matched to that of the FR4. Otherwise the unlike materials will expand at different rates under thermal stress.


More Complex FR4 Hybrid: 12-Layer

Here is a 12-layer hybrid PCB. High frequency material is not required at all positions, so FR4 is used for non-critical layers to save cost.

Refer to the material data sheet when planning a hybrid. It is important that the high frequency material be a type which is compatible with FR4 processing.


Planning Your Design

Design to available thicknesses and types. These are not infinitely variable.

Sheet stock is generally sold in 12x18 or 18x24 sizes. Your PCB (or multiple PCBs) should fit within an area at least 1.50” smaller in both directions. Margins are required for tooling systems, plating clamp locations, etc.

Consider FR4 / HF hybrids whenever practical.


Planning Your Design

Design to available thicknesses and types. These are not infinitely variable.

Sheet stock is generally sold in 12x18 or 18x24 sizes. Your PCB (or multiple PCBs) should fit within an area at least 1.50” smaller in both directions. Margins are required for tooling systems, plating clamp locations, etc.

Consider FR4 / HF hybrids whenever practical.


Summary

It is important to specify the material properties of the PCB type you are designing, by referring to either IPC or manufacturer documents.

Special high frequency materials are available to meet the most critical performance needs.

You can often combine unlike material types within a single design to make your board more economical.

Epec can help you to select appropriate materials for your specific application.

We encourage you to engage early in the design cycle.


Our ProductsBattery Packs Flex & Rigid-Flex PCB’s User Interfaces

Fans & Motors Cable Assemblies Printed Circuit Boards


Design Centers & Technical Support

Battery Pack & Power Management – Denver, CO User Interfaces – Largo, FL Fans & Motors – New Bedford, MA & Wales, UK PCB’s – New Bedford, MA & Shenzhen, China Flex & Rigid Flex – Toronto, Canada Cable Assemblies – Largo, FL

Our Engineering and Design teams are ready to help our customers create world class and cost effective product solutions.


Q&A

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Specifying PCB Laminates to Your Performance Needs