I need to do a reflow of two BGA chips and there are some surface mount components underneath them on their PCB’s. The components are very small capacitors, resistors and possibly inductors (look pictures attached)
Thank you , for contacting Digikey Tech forum we are looking into this , and hoping to have an answer for you as soon as we can.
Here are some links I found relating to this topic:
Ideally, a dot of heat curable adhesive is added to heavier components on the underside before they are reflowed, or they are reflowed using a higher melting point solder than the BGA side solder, but if you are doing rework, this may not be the case. However, it looks like, under most circumstances, with small smt components, solder surface tension is sufficient to hold them in place.
High Temp Masking Liquid - 2538 and 2538UV High-Temp Masking Liquid - 3M | DigiKey
Part Number: 19-2538-ND
Thank you for clarifying the surface tension question.
Could you please give me some guidelines on likely heat tolerance of my small surface mount components (their dimensions given in the first post). Ie: what is the highest temp they are likely to tolerate and for how long? (With my equipment, I cannot keep the temp on the underside of the PCB above 217C for less than 2 min. With the peak temp hitting about 243C. Without any additional thermal protection, is this likely to kill them?).
Thank you for bringing the option of the High Temp Masking Liquid to my attention. However, it is very expensive and this cost doesn’t even take into account the cost of the apparatus to apply it. The cost makes this solution impractical for me. However, do you feel that aluminum tape would be a significantly more heat tolerant product than Kapton tape. Also, would a known brand of aluminum tape or similar product make a critical difference? If a well known tape product can last even to just 250C, without detaching or deforming - that would solve my problem.
Regarding a heat curable adhesive, could you recommend a specific product available from DigiKey (or elsewhere)?
Further regarding High Temp Masking Liquid, perhaps this product is available in smaller quantity and for different dispensing equipment? For example, a small rod the shape of a glue-stick that could be dispensed from a glue gun? This might be able to address the cost issue.
Unfortunately, the High Temp Liquid is only available in the brick form and not smaller qty’s. Here are some tapes that go to 260°C that you can review.
The Loctite 3621, Digi-Key part number 1000-114-ND, is designed for such applications.
Regarding heat tolerance of your components, I really can’t say with certainty. You would have to read the respective documentation of the components used. However, as a general statement, the process of sending parts through a second reflow process to solder parts on the other side of the board is a common practice, so it would seem unlikely that failures would be common under such conditions. Obviously, keeping exposure time and temperature to the minimum required for successful soldering of the other side is desirable.
Have you considered using plumbers putty (or similar) to isolate the chip and surrounding area? It would delay much of the initial heat.
To further delay the heat you could cover the putty with a layer(s) aluminum foil.
HOPE THIS HELPS