How many layers does my PCB have?<\/h2>\n\n\n\n
At first glance, this should be an easy question to answer. 4-layer,\n12-layer, 32-layer PCBs are commonplace and easy to understand \u2013 the number\njust refers to the number of copper layers right?<\/p>\n\n\n\n
Yes, but when it comes to single, double, or even zero-layer PCBs, you might be forced to stop and think before filling in that PCB order form. Is my PCB single or double-layered? Why is there so much confusion? I chose single-layer but my files are actually double-sided \u2013 will they only make single-layer PCBs? Does it really matter? In this article, we try to tackle these points.<\/p>\n\n\n
![\"\"](\"https:\/\/blog.seeedstudio.com\/wp-content\/uploads\/2020\/05\/P1080793-1030x687.jpg\")
Let\u2019s start with some definitions. Traditionally, the number\nof layers of a board refers to the number of copper layers<\/strong>, specifically,\nthe number of layers with copper traces or pour \u2013 just having pads does not\ncount, partly as a safeguard if the design software fails to export the traces\nor pour for whatever reason.<\/p>\n\n\n The simplest type to understand is the surface-mount single-layer PCB board. This is what you\u2019d expect \u2013 traces and pads covered by solder mask and then overlaid with silkscreen printing. There shouldn\u2019t be anything on the other side. No plated through-holes or vias.<\/p>\n\n\n\n GTL, GTS and GTO -> more common This is where things get a little complicated. Beginners\noften forget that a through-hole single-layer board typically needs the\nsilkscreen on the other side of the solder pads. <\/em><\/p>\n\n\n\n GBL, GBS and GTO -> more common The silkscreen typically contains information on the component\noutline, polarity markers and designators\/values. The side with the silkscreen\nprinting is the side where the body of the component lies. The leads are inserted\nthrough the through-holes and soldered to the pads on the opposite side. <\/p>\n\n\n\n The traditional definition does not count copper layers which only contain solder pads as contributing to the layer count. So technically, a single-layer board can also have plated-through holes, so long as one of the sides only contains pads in the copper layer.<\/p>\n\n\n\n GBL (pads only), GBS, GTO, GTL and GTS Plated through-holes, No vias<\/p>\n\n\n\n Which side the traces are on is functionally irrelevant since\nthey are electrically connected via the through-holes, but having them on the\nside with the silkscreen should help with inspection and trouble-shooting. This\ncombination could also support mixed assembly (THT and SMT) if the surface\nmount components are placed on the side with the traces.<\/p>\n\n\n\n Some fab houses may not like this combination and may ask\nyou to confirm how to proceed,<\/p>\n\n\n\n This board is typically the same as the single-layer surface mount except surface mount parts are on both sides. If the two sides form a single circuit, vias are needed to pass the signal through the substrate.<\/p>\n\n\n\n Traces on both copper layers, solder mask on both sides. Can\nhave mixed assembly. Nothing too difficult to understand. Signals can be transmitted\nbetween sides through plated through-holes or vias.<\/p>\n\n\n\n A very special case driven by the increased accessibility of PCB manufacture. A zero-layer board is essentially a board with no copper – it is not designed to be electronically functional but may have solder mask or silkscreen. We sometimes see these when people use our service to make washers, business cards, or customized panel covers for example. This is not common practice, so you will rarely see the option to choose zero-layer boards on any online form.<\/p>\n\n\n\n So that covers most of the oddly defined combinations. Within these, there are other possibilities, but we\u2019ve listed the most common combinations in the table below.<\/p>\n\n\n In my experience, I think the problem is due to different definitions and the lack of specificity. There is no complete definition that clears up the misunderstandings. For example, manufacturers and industry experts often use the terms single-sided<\/strong> and double-sided<\/strong> synonymously with the terms single-layered<\/strong> and double-layered<\/strong>. If we said this is a 4-layer PCB then there is no confusion, but 4 sided doesn\u2019t make sense. So, \u2018sided\u2019 should refer to the top and bottom sides of the PCB, regardless of what is in the middle. Following that logic, a 4-layered PCB is also a double-sided PCB. Notice that we\u2019ve been careful not to say single or double-sided in the article. <\/p>\n\n\n\n As seem, another way of defining a PCB is whether it is for single-sided\nor double-sided assembly. This information is of little importance to a board\nmanufacturer but could add another element of confusion into the conversation. <\/p>\n\n\n\n Certain combinations of Gerber layers may form an exception\nto the standard definitions. From the definition of copper layers, it clearly doesn\u2019t\ncare about the solder mask or silkscreen or even pads. So, to fully define a\nboard you may have something like:<\/p>\n\n\n\n Double-layer boards (for the third example in the table)<\/p>\n\n\n\n With more and more PCB designs that have aesthetics in mind,\nthe lack of solder mask on one side could mean the difference between a quality\nboard and a cheap product. But how do you communicate this in the Gerber files\nand order parameters?<\/p>\n\n\n\n If you like dismantling consumer products, you may have come\nacross single layer PCBs that do not have solder mask on one side, which is\ndesigned to save on production costs. But when was the last time you saw a development\nboard or module on the market with substrate showing through?<\/p>\n\n\n\n Every now and then we see Gerber files sharing similar\ntraits and similar problems. One of those problems is outputting double-layer boards\nwith what seems to be plated through holes but only with pads on one side.\nThere are already two copper layers, so why not make these plated holes? Having\nplated through-holes would allow you to apply more solder to the joint and strengthen\nthe bond.<\/p>\n\n\n\n An increasing number of customers and manufacturers rely on smart Gerber Viewers to automatically detect the layer count of a board and then flag it if there is a discrepancy. How do they do that? Basically, they just count the number of Gerber files named as copper layers. But most can\u2019t tell what is inside the file. So users who rely heavily on these, are tempted to simplify the problem by changing the definition.<\/p>\n\n\n\n Perhaps this should have been the first question since, for 99% of designers, the answer is no. No, you haven’t just wasted 10 minutes reading something completely useless.<\/p>\n\n\n\n Yes and no. It depends on the size of production. For mass production, every consideration should be made into where costs can be minimized. If that means single-sided boards then sure, go for it. If you are just at the prototype stage or going for a small batch, then whether a board is single-sided or not is irrelevant in terms of costs and quite frankly, just complicates things.<\/p>\n\n\n\n It may even involve more work. Double-layer boards are by far much more common than single-layer boards. So manufacturers keep big stocks of cores – FR4 substrate covered on both sides with copper. To make a single layer board, all the copper on one side has to be etched away. <\/p>\n\n\n If too much copper needs to be removed on a panel then the etching solution and etching time may not be sufficient to remove all the copper. In the image above, note the remnants of copper which have been plated with silver HASL surface finish left on the edge of some of the drill holes.<\/p>\n\n\n\n Despite that, single-layer boards typically don’t cost extra. In fact, at Seeed Fusion, we’ve even considered removing the single-layer option entirely \u2013 how many people specifically do NOT want pretty protective solder mask on both sides anyway? The reverse situation is more likely (single-layer boards, double-sided solder mask). Your thoughts? Let us know in the comments section and maybe we will actually do it.<\/p>\n\n\n\n Final question: I chose single-layer but my files are actually double-sided \u2013 will they only make single-layer PCBs? <\/p>\n\n\n\n Most fabs won’t be that drastic and will either ask you to confirm or just follow the files. Another reason why the single layer option doesn’t really matter much.<\/p>\n\n\n\n Congrats on getting through this somewhat long-winded article. We hope it gives you a little insight into the manufacturer’s perspective when it comes to interpreting clients’ intentions. We’ll be bringing more soon!<\/p>\n","protected":false},"excerpt":{"rendered":" With everyone resorting to learning online, there\u2019s no better time to share knowledge freely on<\/p>\n","protected":false},"author":3612,"featured_media":32252,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_lmt_disableupdate":"","_lmt_disable":"","_price":"","_stock":"","_tribe_ticket_header":"","_tribe_default_ticket_provider":"","_tribe_ticket_capacity":"0","_ticket_start_date":"","_ticket_end_date":"","_tribe_ticket_show_description":"","_tribe_ticket_show_not_going":false,"_tribe_ticket_use_global_stock":"","_tribe_ticket_global_stock_level":"","_global_stock_mode":"","_global_stock_cap":"","_tribe_rsvp_for_event":"","_tribe_ticket_going_count":"","_tribe_ticket_not_going_count":"","_tribe_tickets_list":"[]","_tribe_ticket_has_attendee_info_fields":false,"iawp_total_views":0,"footnotes":""},"categories":[4705],"tags":[4,132],"class_list":["post-32248","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-seeed-studio-fusion","tag-pcb","tag-fusion"],"yoast_head":"\n![\"\"](\"https:\/\/blog.seeedstudio.com\/wp-content\/uploads\/2020\/05\/Seeed-Fusion-Abbreviations-List.png\")
So what is a single-layer board?<\/h3>\n\n\n\n
SMT Single-Layer board<\/h4>\n\n\n\n
or
GBL, GBS and GBO<\/p>\n\n\n\nTHT Single-Layer board<\/h4>\n\n\n\n
or
GTL, GTS and GBO <\/p>\n\n\n\nAlso a THT Single-Layer board<\/h4>\n\n\n\n
or
GTL (pads only), GTS, GBO, GBL and GBS<\/p>\n\n\n\nSMT Double-Layer boards<\/h4>\n\n\n\n
THT Double-Layer boards<\/h4>\n\n\n\n
Zero-layer boards<\/h4>\n\n\n\n
![\"\"](\"https:\/\/blog.seeedstudio.com\/wp-content\/uploads\/2020\/05\/Seeed-Fusion-Common-Layer-Definitions-1.png\")
<\/figure><\/div>\n\n\nWhy is there so much confusion?<\/h3>\n\n\n\n
Assembly Types<\/h4>\n\n\n\n
Exceptions<\/h4>\n\n\n\n
\nDouble-sided pads
\nDouble-sided solder mask
\nSingle-sided silkscreen<\/p>\n\n\n\nSome PCB software is to blame<\/h4>\n\n\n\n
Some Smart Gerber viewers encourage\na change of definition<\/h4>\n\n\n\n
Double and Single-sided boards. Does it matter?<\/strong><\/h3>\n\n\n\n
It does not cost more to produce double-layer boards<\/h4>\n\n\n\n
![\"\"](\"https:\/\/blog.seeedstudio.com\/wp-content\/uploads\/2020\/05\/Single-Layer-Copper-etching-2.png\")
<\/figure><\/div>\n\n\n