Selecting PCB core thickness becomes an issue when a gedréckt Circuit Verwaltungsrot (PCB) manufacturer receives a quote requesting a multilayer design and material requirements are incomplete or not stated at all. Heiansdo geschitt dëst well d’Kombinatioun vun PCB Kärmaterialien déi benotzt gi fir d’Performance net wichteg ass; If the overall thickness requirement is met, the end user may not care about the thickness or type of each layer.

But at other times, performance is more important and the thickness needs to be tightly controlled for optimal performance. If the PCB designer clearly communicates all requirements in the documentation, then the manufacturer will know what the requirements are and will set the materials accordingly.

Issues PCB designers need to consider

Et hëlleft Designer d’Material verfügbar ze verstoen an allgemeng benotzt, sou datt se passend Designreegele benotze fir PCBS séier a korrekt ze bauen. Wat folgend ass eng kuerz Beschreiwung vu wéi eng Materialtypen Hiersteller léiwer ze benotzen, a wat se eventuell brauchen fir séier ze rotéieren ouni Äre Projet ze verzögeren.

Understand PCB laminate cost and inventory

It is important to understand that PCB laminate materials are sold and work in a “system” and that the core material and prepreg retained by the manufacturer for immediate use are usually from the same system. In other words, the constituent elements are all parts of a particular product, but with some variations, such as thickness, copper weight and prepreg style. Zousätzlech zu der Bekanntheet an der Widderhuelbarkeet ginn et aner Grënn fir eng limitéiert Unzuel u Laminataarten ze stockéieren.

Prepreg and inner core systems are formulated to work together, but may not work correctly when used in combination with other products. For example, the Isola 370HR core material will not be used in the same stack as the Nelco 4000-13 prepreg. It’s possible they’ll work together in some situations, but more likely they won’t. Hybrid systems take you into uncharted territory, where the behavior of materials (well known when used as homogeneous systems) can no longer be taken for granted. Careless or unwitting mixing and matching of material types can lead to serious failures, so no manufacturer will mix and match unless the type is proven to be suitable for “mixed” stacking.

En anere Grond fir en enke Materialinventar ze halen sinn déi héich Käschte vun der UL Zertifizéierung, sou datt et an der PCB Industrie heefeg ass d’Zuel vun den Zertifizéierungen op eng relativ kleng Auswiel u Material ze limitéieren. Manufacturers will often agree to make products on laminate without standard stock, but be aware that they cannot provide UL certification through QC documentation. This is a good choice for non-UL designs if it is disclosed and agreed in advance and the manufacturer is familiar with the processing requirements of the laminating system in question. For UL work, it is best to find out the manufacturer inventory of your choice and design boards to match it.

Ipc-4101d and foil construction

Now that these facts are out in the open, there are two other things to know before jumping into design. First, it is best to specify laminates according to industry specification IPC-4101D and not to name specific products that not everyone can stock.

Secondly, it is easiest to construct multiple layers using the “foil” construction method. Foil construction means that the top and bottom layers (outer) are made from a single piece of copper foil and laminated to the remaining layers with prepreg. Och wann et intuitiv ausgesäit fir en 8-Schicht PCB mat véier doppelseitegen Kären ze bauen, ass et léiwer fir Folie extern extern ze benotzen, an dann dräi Käre fir L2-L3, L4-L5, a L6-L7. An anere Wierder, plangt e Multi-Layer Stack ze designen sou datt d’Zuel vun de Käre wéi follegt ass: (Gesamtzuel vu Schichten minus 2) gedeelt duerch 2. Als nächst ass et nëtzlech eppes iwwer Kärimmobilien ze wëssen. Selwer.

De Kär gëtt an engem komplett geheelt PIECE vu FR4 geliwwert mat Kupfer plated op béide Säiten. Cores hunn eng breet Palette vun Dicken, a méi allgemeng benotzt Gréisste ginn normalerweis a gréisseren Aktien gelagert. Dëst sinn d’Dicke fir am Kapp ze halen, besonnesch wann Dir séier Wendungsprodukter bestelle musst, sou datt Dir d’Leedzäit vun der Bestellung net verschwënnt waart op net-Standard Material fir vum Distributeur ze kommen.

Common iron core and copper thickness

D’Kären déi am allgemengen benotzt gi fir 0.062 “déck Multilayer ze bauen sinn 0.005”, 0.008 “, 0.014”, 0.021, 0.028 “, an 0.039”. Inventory of 0.047 “is also common, as it is sometimes used to build 2-layer boards. Den anere Kär deen ëmmer gespäichert gëtt ass 0.059 Zoll, well se benotzt gëtt fir 2-Schicht Brieder ze produzéieren déi 0.062 Zoll sinn. Fir dës Positioun limitéiere mir den Ëmfang op e Kärdesign mat enger definitiver nomineller Dicke vun 0.062 Zoll.

Copper thicknesses range from half an ounce to three to four ounces, depending on the particular manufacturer’s product mix, but most stocks can be in two ounces or less. Haalt dëst am Kapp an erënnert Iech datt bal all Aktien datselwecht Kupfergewiicht op béide Säiten vum Kär benotzen. Probéiert PCB Design Ufuerderunge ze vermeiden déi verschidde Kupfer op all Säit erfuerderen, sou dacks erfuerdert dëst e spezielle Kaf a kann e Rush Charge erfuerderen (Rush Liwwerung), heiansdo och net de Mindestbestellung vum Distributeur.

For example, if you want to use 1oz of copper on an airplane and plan to use H oz of signal, consider making the airplane in H oz or increasing the signal to 1oz to make the core use both sides like copper with weight. Natierlech kënnt Dir dëst nëmmen maachen wann Dir ëmmer nach den elektreschen Ufuerderunge vum Design entsprécht an genuch XY Beräicher hutt fir erweidert Spure/Raumdesign Reegelen z’empfänken fir den 1oz Minimum op der Signalschicht z’erreechen. If you can meet these conditions, it is best to use it like a copper weight. Otherwise, you may need to consider a few extra days of lead time.

Assuming that you have selected the appropriate core thickness and available copper weight, various combinations of prepreg sheets are used to establish the remaining dielectric locations until the total thickness required is met. For designs that do not require impedance control, you can leave the prepreg option to the manufacturer. They will use their preferred “standard” version. On the other hand, if you do have impedance requirements, state these requirements in the documentation so that the manufacturer can adjust the amount of prepreg between cores to meet the specified values.

Impedanz Kontroll

Whether impedance control is required or not, it is not recommended that you attempt to document the type and thickness of prepreg for each location unless you are proficient in this practice.Often, such detailed stacks eventually need to be adjusted, so they can cause delays. Amplaz kann Äre Stackdiagram d’Kärdicke vum banneschten Schichtpaar weisen an uginn “prepreg Positioun erfuerderlech baséiert op Impedanz a Gesamtdicke Ufuerderunge”. This allows manufacturers to create ideal laminations to match your design.

De Profil

En ideale Stack Käre baséiert op existente Lager ass kritesch fir onnéideg Verspéidungen ze vermeiden wann Dir séier Wendunge mat strenge Zäitlinnen bestellt. Déi meescht PCB Hiersteller benotzen ähnlech Multilayer Strukturen op Basis vum selwechte Kärel wéi hir Konkurrenten. Ausser wann de PCB héich personaliséiert ass, gëtt et keng Magie oder geheim Konstruktioun. Therefore, it is worth familiarizing yourself with the preferred material for a particular layer and making every effort to design a PCB to match it. Et ginn ëmmer Ausnahmen fir spezifesch Designfuerderunge, awer allgemeng sinn Standardmaterialien déi bescht Wiel.