| Letters |
 |
 |
| Written by Administrator | |||
| Saturday, 31 May 2008 19:00 | |||
Black Pad Has Multiple CausesPhil Zarrow’s April column narrowly assumes causes of black pad. And recommending more gold as mitigation is harmful advice (assuming many readers may miss his 4 µin maximum as the reasonable upper limit). Japanese science has proven, in this case, less is better. Black pad has several causes. The mistake assumes all ENIG chemistries are created equal. We have proven that is not true. Black pad is rare, but can be created by 1) an electroless nickel with less than 5.5% phosphorus content in the plated layer; 2) an overly aggressive gold chemistry (either the chemistry is too acidic, or the gold is permitted to run below recommended levels in the bath, or boards are simply left in the bath too long); 3) the gold layer is too thick (gold deposits by replacing nickel; if this is permitted to continue too long, then the surface is compromised and black pad is guaranteed). We still fight standards (even military: “But that is what the spec says”) that require a minimum 8 µin of immersion gold. Hopefully, such specs also accept total responsibility for black nickel! We also fight erroneous thinking that the solution is high phosphorus nickel (so much for good solderability). The key steps are a consistent nickel and gentle gold that give complete coverage (porous gold layers do not protect the nickel surface) with limited thickness. We prefer two or three µin. As a supplier, this reduces our sales but saves customers money and, most important, it is based on years of research and field service. Another battle fought over the years was the concept of ENIG with a layer of electroless palladium between the nickel and gold (ENEPIG) as the universal finish. However, this does not create as strong a solder joint as regular ENIG, provided leaded solders are used. For non-leaded solders, ENEPIG offers better solderability and eliminates black pad, as the palladium layer acts as a protective barrier between nickel and gold. Another flexible alternative is adding a layer of electroless (autocatalytic) gold over ENIG (a process called ENAG), for purposes of gold wire bonding. Don Walsh Director of Operations Uyemura International Corp. Corrections Due to an editorial error, the April 2008 "Better Manufacturing" column incorrectly stated the IPC standards for gold plating volume in µm. The correct volume is µin. We regret the error. Send your thoughts to Editor, Circuits Assembly, email: This e-mail address is being protected from spambots. You need JavaScript enabled to view it . Letters must include the writer’s name, address and company affiliation and may be edited for length and clarity.
|
Columns
| European RoHS Enforcement Explained |
A series of workshops next month on compliance with RoHS and other directives will help US companies looking to break into the European market. |
| Read more... |
| Believing Foxconn Means Suspending Belief |
The Foxconn makeover is in full swing, with the latest this piece from the New York Times that supposes that the world's largest ODM is worried that Apple -- yes, Apple -- might be bringing it down: |
| Read more... |
Features
| Managing Your ESD Program |
The processes are as important as the tools. |
| Read more... |
| SMT Reflow Oven-to-Oven Repeatability |
How to adjust an oven so a single recipe will work across multiple ovens for an individual product. |
| Read more... |
Search
Search
Login
CB Login
Language
Language
Products
Alpha Introduces Lumet LED Materials
Lumet LED materials are for die attach and package, package on board, Luminaire module, power driver/supply and control systems. Lumet P33 Pb-free, no-clean solder paste for LED package-on-board...
Lumet LED materials are for die attach and package, package on board, Luminaire module, power driver/supply and control systems. Lumet P33 Pb-free, no-clean solder paste for LED package-on-board...
