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Std edition Quick Turn PCB Fabrication

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Published Time: 2018-03-19 14:58:52
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I tried a new quick turn PCB fabrication:JLCPCB , Here is the review about JLCPCB. Since I still have some older versions of one of the boards, I could make a comparison with the two quick turn PCB fabrication. I decide to not mention which competitor I pitched JLCPCB against. What I primarily looked at was how accurately each layer of board is printed and how well they are aligned with one another from each fab service. JLCPCB‘s results are very good. Its competitor, a long-standing name among DIYers, doesn’t look quite as good.

In case you’re still learning how to design PCBs, especially surface-mount components, here are some terms I’m going to use: Top layer: this logic layer contains all copper traces, pads, and vias on the top side of the two-sided circuit board. A process is used to protect all aforementioned features specified in this layer when the entire board is etched in acid. If the process isn’t accurate, then your features aren’t exactly where they are supposed to be.

Top solder paste: this logic layer contains only pads for surface-mount components. It is a subset of top layer and is used to generate stencils for reflow soldering. Again if the fabrication isn’t very good, these features tend to not align with other features. Top solder resist: this logic layer contains similar information to the pads and vias contained in top layer but the sizes of the features in this layer are slightly enlarged to a peel-back amount so they don’t accidentally apply solder resist on top of your pads where solder should go. Solder resist is a lacquer that prevents solder from adhering to the copper traces. They also protect the bare copper from rusting away. You will want them to be applied to all your traces and only leave the pads exposed so later process will cover them with a very thin layer of solder (the shiny looking stuff) and you then reflow solder your components to these pads. If the registration of this layer of lacquer is not well registered with the top layer, you will see visually under a magnifier. This is why fabrication houses usually do quite a bit of peel-back so they leave room for themselves to be less-aligned but still the lacquer won’t cover up the pads. The following images are from an FTDI chip (FT232RL). The pitch was the finest on my board so I selected these pads for comparison of how well the different layers register with one another on these two service providers.

Top: JLCPCB Bottom: competitior

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They look similar. I’ve unfortunately scratched the pads on the competitior’s board. I applied solder paste to that board and later cleaned the paste off so I could photograph its pads. My bad. On a closer look there is a difference:

SMD pads (SSOP 0.65mm pitch): Top: JLCPCB Bottom: competitior

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You can see that JLCPCB’s boards (top) have SMD pads (shiny metal pads) that are very symmetrically situated inside the solder-resist masks (slightly larger dark rectangle). The solder resist also goes closer to the board than its competitior. These are manufactured from the same designs! The engineers at the competitior must have increased the peel-off (sizes of feature not covered by solder resists) to offset their less-perfect layer registrations and/or accuracy on each layer. As you can see, not all pads and their solder resist have the same offset. Some look better than others. This is clear with the second to the last pad and the last pad. The pads are not centered at all. This is very consistent across the board made by competitior. JLCPCB has better overall registration than competitior. Better registration translates into better chance to prevent solder bridges and less chances to reworking on your boards after you reflow them, that means time and money saved.

Thru-hole pads (o.1″ spacing): Top: JLCPCB Bottom: competitior

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The top one has less size solder resist layer, the edges of the red lacquer surrounding the shiny pads (almost same size as the thru-hole pads) and very symmetrical. The competitior has again increased the solder resist layer and couldn’t keep the layer registered well with the pad.

The via to the right of the bottom right through hole pin hole will be compared next. On JLCPCB’s board, its solder resist has 2.8mm diameter when displayed on my computer monitor. On the competitior board, it is 3.1mm. The images were taken under a high-magnification lens and I checked the images to be exactly the same zoom, measuring the same across the same features on screen. What this means is that if you have a lot of vias in one area, very close to one another, you may get some solder bridges between the vias if there is not enough solder resist to separate them. Not a problem on this board but a problem if you happen to have vias very close and also close to thru-hole components. You solder the thru-hole and inevitably fill the adjacent vias with some solder. This could short vias.

Overlay (white texts):

The quality of the white overlay texts are about the same between the two fabricators, although at some places you see one board having better quality than the other board while at different places the quality is reversed. This is not a crucial feature to look at though.

JLCPCB: top, competitior: bottom

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With the explanation above, you can easily distinguish these two photos. The bottom one has so much space between the edges of the shiny pads and the red lacquer (less qualty). The top one has so much less and so symmetric.

So the results are clear. JLCPCB is a pretty decent quick turn PCB fabrication and I will order my next batch from them. The shipping cost is also slightly less than competitior if you use DHL. I always use DHL. They do a good job delivering to small cities like the one I live in!

Here is a link to JLCPCB’s website: jlcpcb.com

P.S.: I had a research student hand solder this board (yes, every single chip resistor and the FTDI chip) as a good test of his skills and it turned out fine. This is a proof that having the right size solder resist helps, really. This is what the board looks like after assembly:

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Read more , please visit :liudr.wordpress.com

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