Hot answers tagged

24

Unless you use via-in-pad, which costs more, you need room to put routing vias in between the pads, like this


19

For cold or dry solders on BGAs, you are working blind without X-ray or just functional testing like yours, so it's not easy for sure. First order of business would be to reflow the BGA with hot air. There are plenty of YouTube videos of GPUs being fixed this way in your home oven with some care. If this does not help and it's your one-off board and not ...


16

Thermal inertia is playing against you. Also take into account that lead-free solder needs temperatures in excess of 220°C to melt down (compared to 180°C for tin-lead solder), so the thermal gradient will be quite high to begin with. Because of this, I would recommend preheating the board to 120°C by using one of the following methods: A preheating plate, ...


14

BGA have a very good thermal contact with PCB- total cross section of all balls is a quite large figure. So before solder type, all PCB is sinking the heat from your BGA. So you have to preheat all of it to 150C, then power flow will become much lower (delta T is lower) and then you will not need more than 300-350C.


13

Having vias placed on a pad is common practice. Nevertheless there are disadvantages which makes designers place vias next to a pad, in some cases even by removing some pads from the BGA footprint. If there is a via in pad, it needs to be filled, either galvanically with copper or with some kind of non-conductive material and then covered in copper. An open ...


11

Advanced PC boards can only be made by little elves in a hollow tree. It is possible for ordinary mortals to make good enough 2 layer board for hobby or prototype purposes, but even that doesn't make sense unless they value their time very little and not look too hard at the cost of screwups due to not having a solder mask, silkscreen, and the hassle of not ...


11

I think you should measure the temperature of your rework station nozzle and soldering iron with a pyrometer. You think your nozzle was at 400°C and your iron at 350°C, but I'm willing to bet they really weren't that hot. Any reasonable solder will melt above 300°C. On a practical note, if you want to salvage BGA components and don't mind to destroy the PCB ...


9

From my experience, one-off assembly is extremely expensive in the US. Most places would not even bother giving me a quote for a single piece. Furthermore, you're likely to have the same problem with building a breakout board, since that will have to be assembled (it just displaces the problem). However, I have found that (with some work), it is possible to ...


9

You imply "all stages" and this seems it may include the actual 8 layer PCB assembly (copper + fibreglass + ... ). If so, don't do it! While PCB construction is a notionally straight forward enough task it requires many processes, each requuring substatial experience and a degree of arcane knowledge to get right consistently. If you are including the ...


8

Vias are often put in pads. There are basically two scenarios. Bottom terminated components For this purpose, I'm referred to leaded and leadless packages with exposed bottom ground pads, but could also include larger transistor packages such as DPAK. These packages are usually used on parts that need a low impedance ground connection, either for thermal ...


7

What happens if you have to route a trace from the center of the BGA to another part of the PCB? On a square grid you may simply route a straight line, but on the hexagonal grid you need a lot of bends. Working with a very fine routing grid within the hexagonal array of balls is no fun and will need a lot more time. Routing with 0 °, 45 ° and 90 ° only will ...


7

Mainly because we need space to route from those pads: In the first picture you show, some 6 layers or more would probably be needed for a decently sized BGA (~400-ish balls). Packing stuff even tighter means that you absolutely need via-in-pad and probably need more layers. This costs more money because it's harder to manufacture. Some smart guy at Texas ...


7

Unfortunately, BGA is not easy to rework. You could try reflowing again, or if you happen to have a via by the pin, shove a bit of flux there and heat with a hot air gun. If that doesn't work you have 1 of 2 options. You can either scrap the board and use a new one, or you can remove the IC, clean all of the pads, then you will have to re-ball the IC. This ...


6

I think it is standard lead-free solder. Your problem with desoldering could be related to many factors. mass of copper in PCB layers quality of soldering station quality of hot-air station


6

Draftspeople at 90° angles The draftsperson who drew the pin map drawing drew it rotated 90° from the draftsperson who drew the package drawing. Rotating it 90° clockwise makes the index pin (A1) match up with the location of the index mark on the top view in the package drawing, as seen below: The top view part, by the way, means exactly what ...


6

You will find that both diagrams actually have exactly the same pin mapping, though it is slightly obfuscated. The first thing we have to do is identify which side is which in the diagrams. In the top diagram we have: On the left we have the top view, which indicates looking down on the top of the chip. On the right we have the bottom view, looking up at ...


6

I think the links were to tie the pads together for plating. Every single pad once had a connection to the outside if I am correct. You can see traces going off the pattern on the top. After plating they CNC route out the connections. Many of the ball pads are tied together in groups for ground and supply rails so only single traces would be required for ...


5

Well a good place to start for questions like these would be the IPC spec PC-7351B not free but it has all the information you'd need about land patterns for most any part. Second I like to use the free version of the pcblibraries tool because it automatically generates IPC compliant footprints from your input data, and can then output or create them in ...


5

You've already accepted an answer, but I'll add this: Keep in mind that all but the smallest (number of balls) and crudest (ball pitch) BGA layouts are going to require expensive multilayer boards- 6 or 8 layers, often not even the relatively inexpensive 4-layer type. Costly per board in small quantities and high up-front NRE costs that get charged every ...


5

Why do you think the BGA is cheaper in assembly? The operation is the same for both: pick and place. But the BGA needs X-ray for inspection, and the assembly shop may charge extra for that. The QFN can be visually inspected. The QFN also lets you reach the pins with a probe. For a scope probe no problem, but for a DMM you'll need needle probes. If you ...


5

AFAIK, there's no significant cost benefit to using BGAs over QFN's. I think the tradeoff is that the BGA is roughly 1/2 the area; whereas the QFN can definitely be routed without microvias. If you don't already need microvias for some other part in your design, adding them to support this part might increase your blank board cost by 50%. On the other hand,...


5

Yes, BGA packages are like little circuit boards. On high pin count devices, in nearly all cases, the balls that lie directly under the die are mostly ground (and sometimes power) connections. The ground balls are fed directly through to the substrate of the die, while the power balls connect to internal power planes. Also, because of their direct metallic ...


5

Yes and no. You can omit pads if you wish however, the following issues can occur. If you run traces under the ball and trust the solder resist to act as an insulator you are likely to get shorts or insulation breakdown/capacitive coupling through the resist. It simply is not intended for that purpose. If you remove too many pads you are reducing the ...


4

Rarely will you need or want to put the capacitor exactly on the power pad. Yes, you'll want to keep it close for best decoupling, but just outside the IC courtyard is very good. As Andy already mentioned, it's generally not recommended to use plated through holes for BGA pads. Even with microvias, there is a tendency for solder to want to wick through the ...


4

Looks like you have a 0.5mm-pitch BGA. You may even have to use via-in-pad and 6 layers to get this to work. Below is a suggested 6-layer layout from Lattice that does not require via-in-pad.


4

As you'll see if you link through to the possible dup, there are ways to do this. My own humble opinion is that they're not very amenable to prototyping using hobbyist methods-- at least for my purposes. I don't say this because I think it's impossible, I say this because I think the yield will be enough under 100% that not knowing whether your mount is ...


3

If the design isn't fixed yet (i.e. pins are free to be changed), then you have some flexibility in what goes where. The first step is to determine what pins are absolutely fixed. For example the FPGA may only have certain resources on some pins - dedicated clock inputs spring to mind, as do high speed transceivers. Depending on the clock network some clock ...


3

In these images, everything that's not black is something - either a via drill, a copper trace or pour, or a silkscreen mark. Unfortunately, it seems that the via drills are not displayed in all of the images - namely the power layer - which makes it a bit confusing. The two dark green circles near the center of the chip on the ground layer are two vias ...


3

No, you do not need solder paste. In fact, if you add solder paste you will probably get some pins shorted. You might want to add some flux which will improve soldering but this is not a must.


3

At the silicon level, you plan to have pins exposed to the outside. The die is pretty much always significantly smaller than the actual, package, so to connect to the pins, bond wires are used. The layout is performed with an idea of where each bond wire is going to go, to give the shortest bond wire for minimal length. On a BGA package, there are no pins ...


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