A question on PCB manufacturing

Thank you everybody. I have a question on PCB manufacturing. I have designed an eight layer board (Top Signal | Power Plane | Gnd | Mid1 Signal | Gnd | Mid 2 signal | Gnd | Bottom Signal). I have some problems with the PCB board. There are five BGA chips on it that according to their montage profile the temperature should reach up to 260 degrees centigrade but the board color and its shape changes as the temperature reaches 220. When I send the problem to the PCB manufacture they said that ere made as regular FR4 material and tin-lead finish and it shouldn=92t use in using RoHS temperature profile. I think they should let me know about possible board montage problem and ask me about this option before start manufacturing it because I said them that this is the first experience of mine. Anyway, I=92m going to reorder the board but I really don=92t know what possible options for the board manufacturing are. What I know is just that A) the board should stand temperature over 260. B) The board should stand multiple montages and de-montage process As the frequency if high, what kind of FR4 board is the best? What is the PCB board electrical test report like? They said to me that they have electrically tested the board but the board had some manufacturing fault? Many thanks

As you say it is your first time, but the professional world does not care about that. You have made some critical errors which are well known areas to avoid to those with experience. You can get some responses on here, but it sounds like you either need a consultant or do alot more research on assembly technology.

I agree you cannot strictly use HASL with lead free BGAs. HASL has pretty much died out for Rohs applications and you should not mix it with lead free stuff, if you want HASL for some critical Rohs exempt application then you need tin/lead based BGAs aswell as they use solder balls, other items with lead free finished terminals can be mixed easily enough.

I use normal FR4 (Tg135 grade material) for my 4 layer lead free boards with 2 lead free BGAs without any problems, but BGA replacement more than once would be a challenge (higher Tg needed for that). I do specify a Hi temperature OSP coating on copper as the normal OSP does not have much of a lifetime after 1st reflow and there is another solder process further down the line. OSP is also nice flat for the assembly. I am a production Engineer not a design Engineer, the designers do not know this stuff (usually), they have other priorities. I would also not take the 260C soldering requirement to literally unless your application is really critical, are you sure its not just a peak temp. My boards don't go over 250C typically (Tier 1 CEM).

Warping under reflow is normally more due to uneven heating or unbalanced copper across the layers or across the PCB area. You could consider using crosshatch for ground plane and filling in any empty spaces with crosshatch plane or unconnected crosshatch.

-- Tony